Autoantibodies to ganglionic acetylcholine receptors in autoimmune autonomic neuropathies

A novel mechanism of idiopathic orthostatic hypotension and hypocatecholaminemia due to autoimmunity against aromatic l-Amino acid decarboxylase

Orthostatic hypotension (OH) is a common condition. Many potential etiologies of OH have been identified, but in clinical practice the underlying cause of OH is often unknown. In the present study, we identified a novel and extraordinary etiology of OH. We describe a first case of acquired severe OH with syncope, and the female patient had extremely low levels of catecholamines and serotonin in plasma, urine and cerebrospinal fluid (CSF). Her clinical and biochemical evidence showed a deficiency of the enzyme aromatic l-amino acid decarboxylase (AADC), which converts l-DOPA to dopamine, and 5-hydroxytryptophan to serotonin, respectively. The consequence of pharmacologic stimulation of catecholaminergic nerves and radionuclide examination revealed her catecholaminergic nerves denervation. Moreover, we found that the patient's serum showed presence of autoantibodies against AADC, and that isolated peripheral blood mononuclear cells (PBMCs) from the patient showed cytokine-induced toxicity against AADC. These observations suggest that her autoimmunity against AADC is highly likely to cause toxicity to adrenal medulla and catecholaminergic nerves which contain AADC, resulting in hypocatecholaminemia and severe OH. Administration of vitamin B6, an essential cofactor of AADC, enhanced her residual AADC activity and drastically improved her symptoms. Our data thus provide a new insight into pathogenesis and pathophysiology of OH.

Autonomic Dysfunction from Diagnosis to Treatment

Autonomic disorders can present with hypotension, gastrointestinal, genitourinary symptoms, and heat intolerance. Diabetes is the most common causes of autonomic failure, and management should focus on glucose control to prevent developing autonomic symptoms. The most prevalent cause of dysautonomia, or autonomic dysfunction, is Postural Orthostatic Tachycardia Syndrome (POTS). Autonomic testing characterizes causes for nonspecific symptoms but is not necessary in patients with classic presentations. Treatment for autonomic dysfunction and failure focus on discontinuing offending medications, behavioral modification, and pharmacologic therapy to decrease symptom severity. Autonomic failure has no cure; therefore, the focus remains on improving quality of life.

The Presence of Ganglionic Acetylcholine Receptor Antibodies in Sera from Patients with Functional Gastrointestinal Disorders: A Preliminary Study

BACKGROUND

Functional gastrointestinal disorders (FGIDs), including functional dyspepsia (FD) and irritable bowel syndrome (IBS), are characterized by chronic and recurrent gastrointestinal symptoms. Clinically, FD and IBS often resemble gastrointestinal dysmotility caused by autoimmune autonomic neuropathy. We examined the seropositive frequency of autoantibodies against ganglionic nicotinic acetylcholine receptors (gnAChRs) in patients presenting with FGIDs.

OBJECTIVE

To elucidate the seropositivity of gnAChR antibodies and the clinical features of seropositive FD and IBS.

MATERIALS AND METHODS

We measured autoantibodies against the gnAChR α3 and β4subunits using luciferase immunoprecipitation systems. Serum samples from patients with any autonomic symptoms were obtained from hospitals in Japan between January 2012 and August 2018 (1787 serum samples of 1381 patients). We selected FD and IBS patients and compared the clinical characteristics and prevalence of autonomic symptoms between those with seropositive and seronegative IBS and FD.

RESULTS

Nine IBS and two FD cases (one comorbid case with IBS) were found. We found four patients (36.4%) in whom gnAChR antibodies were positive in these eleven patients. Sicca symptoms were observed in three of four cases (75%) of seropositive FGID compared with zero of seven cases (0%) of seronegative FGID.

CONCLUSIONS

We found patients with gnAChR antibodies in FD and IBS patients. These data will be valuable for elucidating the pathophysiology of these FGIDs and developing new treatment strategies.

Autoimmunity in Syndromes of Orthostatic Intolerance: An Updated Review

Orthostatic intolerance is a broad term that represents a spectrum of dysautonomic disorders, including postural orthostatic tachycardia syndrome (POTS) and orthostatic hypotension (OH), as manifestations of severe autonomic failure. While the etiology of orthostatic intolerance has not yet fully been uncovered, it has been associated with multiple underlying pathological processes, including peripheral neuropathy, altered renin-aldosterone levels, hypovolemia, and autoimmune processes. Studies have implicated adrenergic, cholinergic, and angiotensin II type I autoantibodies in the pathogenesis of orthostatic intolerance. Several case series have demonstrated that immunomodulation therapy resulted in favorable outcomes, improving autonomic symptoms in POTS and OH. In this review, we highlight the contemporary literature detailing the association of autoimmunity with POTS and OH.

Serum autoantibodies against α7-nicotinic receptors in subgroups of patients with bipolar disorder or schizophrenia: clinical features and link with peripheral inflammation

There is growing evidence that autoantibodies (AAbs) against proteins expressed in the brain are playing an important role in neurological and psychiatric disorders. Here, we explore the presence and the role of peripheral AAbs to the α7-nicotinic acetylcholine receptor (nAChR) in inflammatory subgroups of psychiatric patients with bipolar disorder (BD) or schizophrenia (SCZ) and healthy controls. We have identified a continuum of AAb levels in serum when employing a novel ELISA technique, with a significant elevation in patients compared to controls. Using unsupervised two-step clustering to stratify all the subjects according to their immuno-inflammatory background, we delineate one subgroup consisting solely of psychiatric patients with severe symptoms, high inflammatory profile, and significantly increased levels of anti-nAChR AAbs. In this context, we have used monoclonal mouse anti-human α7-nAChR antibodies (α7-nAChR-mAbs) and shown that TNF-α release was enhanced upon LPS stimulation in macrophages pre-incubated with α7-nAChR-mAbs compared to the use of an isotype control. These findings provide a basis for further study of circulating nicotinic AAbs, and the inflammatory profile observed in patients with major mood and psychotic disorders.

Autoimmune Autonomic Neuropathy: From Pathogenesis to Diagnosis

Autoimmune autonomic ganglionopathy (AAG) is a disease of autonomic failure caused by ganglionic acetylcholine receptor (gAChR) autoantibodies. Although the detection of autoantibodies is important for distinguishing the disease from other neuropathies that present with autonomic dysfunction, other factors are important for accurate diagnosis. Here, we provide a comprehensive review of the clinical features of AAG, highlighting differences in clinical course, clinical presentation, and laboratory findings from other neuropathies presenting with autonomic symptoms. The first step in diagnosing AAG is careful history taking, which should reveal whether the mode of onset is acute or chronic, followed by an examination of the time course of disease progression, including the presentation of autonomic and extra-autonomic symptoms. AAG is a neuropathy that should be differentiated from other neuropathies when the patient presents with autonomic dysfunction. Immune-mediated neuropathies, such as acute autonomic sensory neuropathy, are sometimes difficult to differentiate, and therefore, differences in clinical and laboratory findings should be well understood. Other non-neuropathic conditions, such as postural orthostatic tachycardia syndrome, chronic fatigue syndrome, and long COVID, also present with symptoms similar to those of AAG. Although often challenging, efforts should be made to differentiate among the disease candidates.

Dysautonomia following Lyme disease: a key component of post-treatment Lyme disease syndrome?

Dysautonomia, or dysfunction of the autonomic nervous system (ANS), may occur following an infectious insult and can result in a variety of debilitating, widespread, and often poorly recognized symptoms. Dysautonomia is now widely accepted as a complication of COVID-19 and is an important component of Post-Acute Sequelae of COVID-19 (PASC or long COVID). PASC shares many overlapping clinical features with other infection-associated chronic illnesses including Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS) and Post-Treatment Lyme Disease Syndrome (PTLDS), suggesting that they may share common underlying mechanisms including autonomic dysfunction. Despite the recognition of this complication of Lyme disease in the care of patients with PTLD, there has been a scarcity of research in this field and dysautonomia has not yet been established as a complication of Lyme disease in the medical literature. In this review, we discuss the evidence implicating Borrelia burgdorferi as a cause of dysautonomia and the related symptoms, propose potential pathogenic mechanisms given our knowledge of Lyme disease and mechanisms of PASC and ME/CFS, and discuss the diagnostic evaluation and treatments of dysautonomia. We also outline gaps in the literature and priorities for future research.

Chronic intestinal pseudo-obstruction in adults: A practical guide to identify patient subgroups that are suitable for more specific treatments

Chronic intestinal pseudo-obstruction is a rare and heterogeneous syndrome characterized by recurrent symptoms of intestinal obstruction with radiological features of dilated small or large intestine with air/fluid levels in the absence of any mechanical occlusive lesion. Several diseases may be associated with chronic intestinal pseudo-obstruction and in these cases, the prognosis and treatment are related to the underlying disease. Also, in its "primary or idiopathic" form, two subgroups of patients should be determined as they require a more specific therapeutic approach: patients whose chronic intestinal pseudo-obstruction is due to sporadic autoimmune/inflammatory mechanisms and patients whose neuromuscular changes are genetically determined. In a context of a widely heterogeneous adult population presenting chronic intestinal pseudo-obstruction, this review aims to summarize a practical diagnostic workup for identifying definite subgroups of patients who might benefit from more specific treatments, based on the etiology of their underlying condition.

Paraneoplastic neuropathies and peripheral nerve hyperexcitability disorders

Peripheral neuropathy is a common referral for patients to the neurologic clinics. Paraneoplastic neuropathies account for a small but high morbidity and mortality subgroup. Symptoms include weakness, sensory loss, sweating irregularity, blood pressure instability, severe constipation, and neuropathic pain. Neuropathy is the first presenting symptom of malignancy among many patients. The molecular and cellular oncogenic immune targets reside within cell bodies, axons, cytoplasms, or surface membranes of neural tissues. A more favorable immune treatment outcome occurs in those where the targets reside on the cell surface. Patients with antibodies binding cell surface antigens commonly have neural hyperexcitability with pain, cramps, fasciculations, and hyperhidrotic attacks (CASPR2, LGI1, and others). The antigenic targets are also commonly expressed in the central nervous system, with presenting symptoms being myelopathy, encephalopathy, and seizures with neuropathy, often masked. Pain and autonomic components typically relate to small nerve fiber involvement (nociceptive, adrenergic, enteric, and sudomotor), sometimes without nerve fiber loss but rather hyperexcitability. The specific antibodies discovered help direct cancer investigations. Among the primary axonal paraneoplastic neuropathies, pathognomonic clinical features do not exist, and testing for multiple antibodies simultaneously provides the best sensitivity in testing (AGNA1-SOX1; amphiphysin; ANNA-1-HU; ANNA-3-DACH1; CASPR2; CRMP5; LGI1; PCA2-MAP1B, and others). Performing confirmatory antibody testing using adjunct methods improves specificity. Antibody-mediated demyelinating paraneoplastic neuropathies are limited to MAG-IgM (IgM-MGUS, Waldenström's, and myeloma), with the others associated with cytokine elevations (VEGF, IL6) caused by osteosclerotic myeloma, plasmacytoma (POEMS), and rarely angiofollicular lymphoma (Castleman's). Paraneoplastic disorders have clinical overlap with other idiopathic antibody disorders, including IgG4 demyelinating nodopathies (NF155 and Contactin-1). This review summarizes the paraneoplastic neuropathies, including those with peripheral nerve hyperexcitability.

Autonomic nervous system involvement in autoimmune encephalitis and paraneoplastic neurological syndromes

In autoimmune neurological diseases, the autonomic nervous system can be the primary target of autoimmunity (e.g. autoimmune autonomic ganglionopathy), or, more frequently, be damaged together with other areas of the nervous system (e.g. Guillain-Barré syndrome). Patients with autoimmune encephalitis and paraneoplastic neurological syndromes (PNS) often develop dysautonomia; however, the frequency and spectrum of autonomic signs and symptoms remain ill defined except for those scenarios in which dysautonomia is a core feature of the disease. Such is the case of Lambert-Eaton myasthenic syndrome, Morvan syndrome or anti-NMDAR encephalitis; in the latter, patients with dysautonomia have been reported to carry a more severe disease and to retain higher disability than those without autonomic dysfunction. Likewise, the presence of autonomic involvement indicates a higher risk of death due to neurological cause in patients with anti-Hu PNS. However, in anti-Hu and other PNS, as well as in the context of immune checkpoint inhibitors' toxicities, the characterization of autonomic involvement is frequently overshadowed by the severity of other neurological symptoms and signs. When evaluated with tests specific for autonomic function, patients with autoimmune encephalitis or PNS usually show a more widespread autonomic involvement than clinically suggested, which may reflect a potential gap of care when it comes to diagnosing dysautonomia. This review aims to revise the autonomic involvement in patients with autoimmune encephalitis and PNS, using for that purpose an antibody-based approach. We also discuss and provide general recommendations for the evaluation and management of dysautonomia in these patients.

Paraneoplastic autonomic neuropathies and GI dysmotility

A number of the well-recognized autoimmune and paraneoplastic neurologic syndromes commonly involve the autonomic nervous system. In some cases, the autonomic nerves or ganglia are primary targets of neurologic autoimmunity, as in immune-mediated autonomic ganglionopathies. In other disorders such as encephalitis, autonomic centers in the brain may be affected. The presence of autonomic dysfunction (especially gastrointestinal dysmotility) is sometimes overlooked even though this may contribute significantly to the symptom burden in these paraneoplastic disorders. Additionally, recognition of autonomic features as part of the clinical syndrome can help point the diagnostic evaluation toward autoimmune and paraneoplastic etiologies. As with other paraneoplastic disorders, the clinical syndrome and the presence and type of neurologic autoantibodies help to secure the diagnosis and direct the most appropriate investigation for malignancy. Optimal management for these conditions typically includes aggressive treatment of the neoplasm, immunomodulatory therapy, and symptomatic treatments for orthostatic hypotension and gastrointestinal dysmotility.

Paraneoplastic autoimmune neurologic disorders associated with thymoma

Thymoma is often associated with paraneoplastic neurologic diseases. Neural autoantibody testing is an important tool aiding diagnosis of thymoma and its autoimmune neurologic complications. Autoantibodies specific for muscle striational antigens and ion channels of the ligand-gated nicotinic acetylcholine receptor superfamily are the most prevalent biomarkers. The autoimmune neurologic disorders associating most commonly with thymoma are myasthenia gravis (MG), peripheral nerve hyperexcitability (neuromyotonia and Morvan syndrome), dysautonomia, and encephalitis. Patients presenting with these neurologic disorders should be screened for thymoma at diagnosis. Although they can cause profound disability, they usually respond to immunotherapy and treatment of the thymoma. Worsening of the neurologic disorder following surgical removal of a thymoma may herald tumor recurrence. Prompt recognition of paraneoplastic neurologic disorders is critical for patient management. A multidisciplinary approach is required for optimal management of neurologic autoimmunity associated with thymoma.

Epidemiology of paraneoplastic neurologic syndromes

Paraneoplastic neurologic syndromes (PNS), initially depicted as seemingly cryptic remote manifestations of malignancy, were first described clinically in the early 20th century, with pathophysiologic correlates becoming better elucidated in the latter half of the century. There remain many questions not only about the pathophysiology but also regarding the epidemiology of these conditions. The continuous discovery of novel autoantigens and related neurologic disease has broadened the association in classical PNS to include conditions such as paraneoplastic cerebellar degeneration. It has also brought into focus several other neurologic syndromes with a putative neoplastic association. These conditions are overall rare, making it difficult to capture large numbers of patients to study, and raising the question of whether incidence is increasing over time or improved identification is driving the increased numbers of cases. With the rise and increasing use of immunotherapy for cancer treatment, the incidence of these conditions is additionally expected to rise and may present with various clinical symptoms. As we enter an era of clinical trial intervention in these conditions, much work is needed to capture more granular data on population groups defined by socioeconomic characteristics such as age, ethnicity, economic resources, and gender to optimize care and clinical trial planning.

Functional autoantibodies: Definition, mechanisms, origin and contributions to autoimmune and non-autoimmune disorders

A growing body of evidence underscores the relevance of functional autoantibodies in the development of various pathogenic conditions but also in the regulation of homeostasis. However, the definition of functional autoantibodies varies among studies and a comprehensive overview on this emerging topic is missing. Here, we do not only explain functional autoantibodies but also summarize the mechanisms underlying the effect of such autoantibodies including receptor activation or blockade, induction of receptor internalization, neutralization of ligands or other soluble extracellular antigens, and disruption of protein-protein interactions. In addition, in this review article we discuss potential triggers of production of functional autoantibodies, including infections, immune deficiency and tumor development. Finally, we describe the contribution of functional autoantibodies to autoimmune diseases including autoimmune thyroid diseases, myasthenia gravis, autoimmune pulmonary alveolar proteinosis, autoimmune autonomic ganglionopathy, pure red cell aplasia, autoimmune encephalitis, pemphigus, acquired thrombotic thrombocytopenic purpura, idiopathic dilated cardiomyopathy and systemic sclerosis, as well as non-autoimmune disorders such as allograft rejection, infectious diseases and asthma.

COVID-19-Induced Postural Orthostatic Tachycardia Syndrome and Dysautonomia

Postural orthostatic tachycardia syndrome (POTS) is a disorder characterized by orthostatic intolerance and, by definition, includes clinical symptoms of lightheadedness, palpitations, and tremulousness among others. It is considered a relatively rare condition that affects approximately 0.2% of the general population, and it is estimated that between 500,000 to 1,000,000 individuals in the United States have the condition and recently has been linked to post-infectious (viral) etiologies. We present a case of a 53-year-old woman who was diagnosed with POTS following extensive autoimmune workup, who was also status post-severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. The post-coronavirus disease 2019 (COVID-19) cardiovascular autonomic dysfunction can affect global circulatory control, which describes increased heart rate even at resting states, and local circulatory disorders, such as coronary microvascular disease leading to vasospasm, as described by the patient's chest pain, and venous retention leading to pooling and reduced venous return after standing. Along with tachycardia with orthostatic intolerance, other symptoms can also accompany the syndrome. In the majority of patients, intravascular volume is reduced, leading to decreased venous return to the heart and causing reflex tachycardia and orthostatic intolerance. Management varies from lifestyle modifications to pharmacologic therapy, to which patients generally show a good response. POTS should be a differential on the cards, especially in patients post-COVID-19 infection, as these symptoms can be misdiagnosed as having psychological etiologies.

Autoimmunity to Neuronal Nicotinic Acetylcholine Receptors

Nicotinic acetylcholine receptors (nAChRs) are widely expressed in many and diverse cell types, participating in various functions of cells, tissues and systems. In this review, we focus on the autoimmunity against neuronal nAChRs, the specific autoantibodies and their mechanisms of pathological action in selected autoimmune diseases. We summarize the current relevant knowledge from human diseases as well as from experimental models of autoimmune neurological disorders related to antibodies against neuronal nAChR subunits. Despite the well-studied high immunogenicity of the muscle nAChRs where autoantibodies are the main pathogen of myasthenia gravis, autoimmunity to neuronal nAChRs seems infrequent, except for the autoantibodies to the ganglionic receptor, the α3 subunit containing nAChR (α3-nAChR), which are detected and are likely pathogenic in Autoimmune Autonomic Ganglionopathy (AAG). We describe the detection, presence and function of these antibodies and especially the recent development of a cell-based assay (CBA) which, contrary to until recently available assays, is highly specific for AAG. Rare reports of autoantibodies to the other neuronal nAChR subtypes include a few cases of antibodies to α7 and/or α4β2 nAChRs in Rasmussen encephalitis, schizophrenia, autoimmune meningoencephalomyelitis, and in some myasthenia gravis patients with concurrent CNS symptoms. Neuronal-type nAChRs are also present in several non-excitable tissues, however the presence and possible role of antibodies against them needs further verification. It is likely that the future development of more sensitive and disease-specific assays would reveal that neuronal nAChR autoantibodies are much more frequent and may explain the mechanisms of some seronegative autoimmune diseases.

En mann i 50-årene med nærbesvimelser og vedvarende svimmelhet

BACKGROUND

A previously healthy male patient in his fifties presented with subacute onset of severe, diffuse dysautonomia with orthostatic hypotension as the main symptom. A lengthy interdisciplinary workup revealed a rare condition.

CASE PRESENTATION

Over the course of a year, the patient was twice admitted to the local department of internal medicine because of severe hypotension. Testing showed severe orthostatic hypotension with normal cardiac function tests and no apparent underlying cause. On referral to neurological examination, symptoms of a broader autonomic dysfunction were discovered, with symptoms of xerostomia, irregular bowel habits, anhidrosis and erectile dysfunction. The neurological examination was normal, except for bilateral mydriatic pupils. The patient was tested for ganglionic acetylcholine receptor (gAChR) antibodies. A strong positive result confirmed the diagnosis of autoimmune autonomic ganglionopathy. There were no signs of underlying malignancy. The patient received induction treatment with intravenous immunoglobulin and later maintenance treatment with rituximab, resulting in significant clinical improvement.

INTERPRETATION

Autoimmune autonomic ganglionopathy is a rare but likely underdiagnosed condition, which may cause limited or widespread autonomic failure. Approximately half of the patients have ganglionic acetylcholine receptor antibodies in serum. It is important to diagnose the condition as it can cause high morbidity and mortality, but responds to immunotherapy.

Anti-ganglionic acetylcholine receptor antibodies in functional neurological symptom disorder/conversion disorder

Objective

Autoimmune autonomic ganglionopathy (AAG) is a rare disorder characterized by autonomic failure associated with the presence of anti-ganglionic acetylcholine receptor (gAChR) antibodies; however, several studies have reported that individuals with anti-gAChR antibodies present with central nervous system (CNS) symptoms such as impaired consciousness and seizures. In the present study, we investigated whether the presence of serum anti-gAChR antibodies correlated with autonomic symptoms in patients with functional neurological symptom disorder/conversion disorder (FNSD/CD).

Methods

Clinical data were collected for 59 patients presenting with neurologically unexplained motor and sensory symptoms at the Department of Neurology and Geriatrics between January 2013 and October 2017 and who were ultimately diagnosed with FNSD/CD according to the Diagnostic and Statistical Manual of Mental Disorders, 5th Edition. Correlations between serum anti-gAChR antibodies and clinical symptoms and laboratory data were analyzed. Data analysis was conducted in 2021.

Results

Of the 59 patients with FNSD/CD, 52 (88.1%) exhibited autonomic disturbances and 16 (27.1%) were positive for serum anti-gAChR antibodies. Cardiovascular autonomic dysfunction, including orthostatic hypotension, was significantly more prevalent (75.0 vs. 34.9%, P = 0.008), whereas involuntary movements were significantly less prevalent (31.3 vs. 69.8%, P = 0.007), among anti-gAChR antibody-positive compared with -negative patients. Anti-gAChR antibody serostatus did not correlate significantly with the frequency of other autonomic, sensory, or motor symptoms analyzed.

Conclusions

An autoimmune mechanism mediated by anti-gAChR antibodies may be involved in disease etiology in a subgroup of FNSD/CD patients.

Postural orthostatic tachycardia syndrome: New concepts in pathophysiology and management

Postural orthostatic tachycardia syndrome (POTS) is a common and therapeutically challenging condition affecting numerous people worldwide. Recent studies have begun to shed light on the pathophysiology of this disorder. At the same time, both non-pharmacologic and pharmacologic therapies have emerged that offer additional treatment options for those afflicted with this condition. This paper reviews new concepts in both the pathophysiology and management of POTS.

Anti-ganglionic nicotinic acetylcholine receptor α3 subunit antibody as a potential biomarker associated with lupus enteritis

OBJECTIVES

We aimed to identify the clinical significance of anti-ganglionic nicotinic acetylcholine receptor α3 subunit (gAChRα3) antibodies (Abs) in patients with systemic lupus erythematosus (SLE).

METHODS

This retrospective study comprised adult patients with SLE who visited our hospital from 2006 through 2019. Anti-gAChRα3 Abs were measured in the sera of patients with SLE using a luciferase immunoprecipitation system assay. The clinical features of the patients with or without anti-gAChRα3 Abs were compared. We evaluated whether the Abs predict a specific manifestation and affect its development or relapse rate.

RESULTS

Among 144 patients, anti-gAChRα3 Abs were detected in 29 patients. Lupus enteritis (LE) was more frequently seen in anti-gAChRα3 Ab-positive patients than negative patients. The levels of anti-gAChRα3 Abs were significantly higher in patients with LE than those with other lupus manifestations. Logistic regression analysis revealed the anti-gAChRα3 Abs were independent predictors for LE (odds ratio 6.2, 95% confidence interval 1.9-20.3, p = .002). Kaplan-Meier analysis showed the rate of LE development or relapse from the time of sera collection was higher in anti-gAChRα3 Ab-positive patients than in negative patients (p < .001).

CONCLUSION

Anti-gAChRα3 Abs could be a predictive biomarker for the development or relapse of LE.

Postural Orthostatic Tachycardia Syndrome in COVID-19: A Contemporary Review of Mechanisms, Clinical Course and Management

The long-term implications of COVID-19 have garnered increasing interest in recent months, with Long-COVID impacting over 65 million individuals worldwide. Postural orthostatic tachycardia syndrome (POTS) has emerged as an important component of the Long-COVID umbrella, estimated to affect between 2 and 14% of survivors. POTS remains very challenging to diagnose and manage - this review aims to provide a brief overview of POTS as a whole and goes on to summarize the available literature pertaining to POTS in the setting of COVID-19. We provide a review of available clinical reports, outline proposed pathophysiological mechanisms and end with a brief note on management considerations.

Autonomic failure: Clinicopathologic, physiologic, and genetic aspects

Over the past century, generations of neuroscientists, pathologists, and clinicians have elucidated the underlying causes of autonomic failure found in neurodegenerative, inherited, and antibody-mediated autoimmune disorders, each with pathognomonic clinicopathologic features. Autonomic failure affects central autonomic nervous system components in the α-synucleinopathy, multiple system atrophy, characterized clinically by levodopa-unresponsive parkinsonism or cerebellar ataxia, and pathologically by argyrophilic glial cytoplasmic inclusions (GCIs). Two other central neurodegenerative disorders, pure autonomic failure characterized clinically by deficits in norepinephrine synthesis and release from peripheral sympathetic nerve terminals; and Parkinson's disease, with early and widespread autonomic deficits independent of the loss of striatal dopamine terminals, both express Lewy pathology. The rare congenital disorder, hereditary sensory, and autonomic neuropathy type III (or Riley-Day, familial dysautonomia) causes life-threatening autonomic failure due to a genetic mutation that results in loss of functioning baroreceptors, effectively separating afferent mechanosensing neurons from the brain. Autoimmune autonomic ganglionopathy caused by autoantibodies targeting ganglionic α3-acetylcholine receptors instead presents with subacute isolated autonomic failure affecting sympathetic, parasympathetic, and enteric nervous system function in various combinations. This chapter is an overview of these major autonomic disorders with an emphasis on their historical background, neuropathological features, etiopathogenesis, diagnosis, and treatment.

Resting heart rate variability as a diagnostic marker of cardiovascular dysautonomia in postural tachycardia syndrome

OBJECTIVES

Postural orthostatic tachycardia syndrome (POTS) is a disorder of the autonomic nervous system characterised by orthostatic intolerance and orthostatic tachycardia without hypotension. Heart rate variability (HRV) is the most reliable and objective tool for assessing autonomic dysfunction severity. In the present study, we aimed to investigate HRV changes in resting supine position, predicting severity and cardiovascular risk in patients with POTS.

METHODS

We compared 100 POTS patients with 160 healthy controls matched for age and gender in a case-control design. Along with clinical characterization, heart rate variability was evaluated using ambulatory 5 min ECG in lead II and expressed in frequency and time-domain measures.

RESULTS

The resting heart rate of patients with POTS was significantly higher than that of healthy controls. In HRV measures, root mean square successive difference of RR intervals (RMSSD), total and high frequency (HF) powers were statistically lower with an increased low frequency (LF) to high-frequency ratio in patients with POTS compared to healthy controls. Further, stepwise logistic regression analysis showed increased basal HR and LF/HF as significant predictors of POTS and its severity.

CONCLUSIONS

This is the first study on a large cohort of patients with POTS from India wherein HRV was assessed. The study showed reduced parasympathetic activity and increased sympathetic activity in patients with POTS compared to healthy controls. These findings of increased resting heart rate and LF/HF were found to be potential predictors of POTS and future cardiovascular risks, which need to be replicated in a larger and more homogenized cohort.

Severe treatment-refractory antibody positive autoimmune autonomic ganglionopathy after mRNA COVID19 vaccination

BACKGROUND

COVID-19 vaccine-associated peripheral and central neuroimmunological disorders have been well described. We present the case of a 56 year old male who developed α3-ganglionic AChR antibody positive Autoimmune Autonomic Ganglionopathy (AAG) after completion of a two-dose course of mRNA (Comirnaty) vaccination for COVID19.

RESULTS

A previously hypertensive 56 year old male presented with the subacute onset of severe constipation, urinary retention, erectile dysfunction, sudomotor failure, sicca symptoms, non-reactive pupils and severe orthostatic hypotension shortly after receiving the second dose of an mRNA vaccine against COVID19. Autonomic testing revealed severe cardiovagal, adrenergic and sudomotor impairment, and tonic 'half-mast' pupils with evidence of sympathetic and parasympathetic denervation. Pathological α3-ganglionic ACHR antibodies were positive in serum as detected by a new flow cytometric immunomodulation assay. Malignancy was excluded. The patient was diagnosed with severe, treatment-refractory acute AAG.

CONCLUSIONS

While autonomic dysfunction has been previously reported post-COVID19 vaccination, to our knowledge this is the first reported case of antibody-positive AAG in this setting. The severity of this case is in marked contrast to the existing literature on idiopathic antibody-positive autoimmune pandysautonomia.

[Over 5 years follow-up of three cases of autoimmune autonomic ganglionopathy]

We report the clinical course of three cases of anti-ganglionic acetylcholine receptor (gAChR) antibody positive auto-immune autonomic ganglionopathy (AAG) that have been followed for over 5 years. In all three cases, the symptoms improved by acute treatment, but ultimately relapsed. The first case was a female in her 20s who had a chronic history of photophobia, constipation and amenorrhea. The symptoms almost disappeared by plasma exchange, and menstruation resumed. During the course, it relapsed once after a cold. There was no recurrence of AAG during the two pregnancies. The second case was a male in his 60s who visited a hospital for the acute onset of orthostatic hypotension (OH) and psychological symptoms (infantilization and psychogenic pseudosyncope). Although IVIg was effective, it recurred frequently and was difficult to treat. However, all the symptoms disappeared eight years after the onset without any particular reasons. The third case was a female in her 80s who had a chronic history of OH. Acute treatment was effective, but AAG recurred repeatedly. Additionally, it was difficult to judge relapse because of the residual sequelae. During the course, cerebral hemorrhage due to supine hypertension or short-time blood pressure variability and femoral neck fracture caused by OH occurred. She eventually became a wheelchair. This report is clinically important because there are few reports of long-term follow-up of AAG.

A novel murine model of autoimmune dysautonomia by α3 nicotinic acetylcholine receptor immunization

We aimed to establish a novel murine model of autoimmune autonomic ganglionopathy (AAG), which represents autoimmune dysautonomia, associated with MHC class II to understand its pathomechanism and the pathogenicity of nicotinic acetylcholine receptor (nAChR) antibodies. The amino acid sequence of the mouse nAChRα3 protein was analyzed using an epitope prediction tool to predict the possible MHC class II binding mouse nAChRα3 peptides. We focused on two nAChRα3 peptides in the extracellular region, and experimental AAG (EAAG) was induced by immunization of C57BL/6 mice with these two different peptides. EAAG mice were examined both physiologically and histologically. Mice with EAAG generated nAChRα3 antibodies and exhibited autonomic dysfunction, including reduced heart rate, excessive fluctuations in systolic blood pressure, and intestinal transit slowing. Additionally, we observed skin lesions, such as alopecia and skin ulcers, in immunized mice. Neuronal cell density in the sympathetic cervical ganglia in immunized mice was significantly lower than that in control mice at the light microscopic level. We interpreted that active immunization of mice with nAChRα3 peptides causes autonomic dysfunction similar to human AAG induced by an antibody-mediated mechanism. We suggested a mechanism by which different HLA class II molecules might preferentially affect the nAChR-specific immune response, thus controlling diversification of the autoantibody response. Our novel murine model mimics AAG in humans and provides a useful tool to investigate its pathomechanism.

Effectiveness of treatment for 31 patients with seropositive autoimmune autonomic ganglionopathy in Japan

Background:

Autoimmune autonomic ganglionopathy (AAG) is characterized by serum autoantibodies against the ganglionic acetylcholine receptor (gAChR). Immunomodulatory treatments may alleviate AAG symptoms, but the most appropriate treatment strategy is unclear.

Objective:

This study aimed to confirm the effectiveness of treatments, particularly immunotherapy, in patients with seropositive AAG in Japan, as well as to determine the most effective treatment and the best assessment method for clinical response to treatment.

Methods:

We collected data from a previous cohort study of patients with seropositive AAG. The clinical autonomic and extra-autonomic symptoms were objectively counted and subjectively assessed using the modified Composite Autonomic Symptom Score. Post-treatment changes in the gAChR antibody level were evaluated.

Results:

Thirty-one patients received immunotherapy. Among them, 19 patients received intravenous methylprednisolone; 27, intravenous immunoglobulin; 3, plasma exchange; 18, oral steroids; 2, tacrolimus; 1, cyclosporine; and 1, mycophenolate mofetil. Patients who received immunotherapy showed improvements in the total number of symptoms (from 6.2 ± 2.0 to 5.1 ± 2.0) and modified Composite Autonomic Symptom Score (from 37.4 ± 15.3 to 26.6 ± 12.8). Orthostatic intolerance, sicca, and gastrointestinal symptoms were ameliorated by immunotherapy. Immunotherapy decreased the antibody levels (gAChRα3 antibodies, from 2.2 ± 0.4 to 1.9 ± 0.4, p = 0.08; gAChRβ4 antibodies, from 1.6 ± 0.1 to 1.0 ± 0.2, p = 0.002), but antibody levels increased in 10 patients despite immunotherapy. The rate of improvement in the total number of symptoms was higher in patients with combined therapy than in patients with non-combined therapy (70.7% vs 28.6%).

Conclusions:

The scores in many items on the rating scale decreased after immunotherapy in patients with seropositive AAG, particularly in the combined immunotherapy group. However, more accurate assessment scales for clinical symptoms and multicenter randomized, placebo-controlled prospective studies are warranted to establish future treatment strategies.

The mosaic of autoimmunity - Finally discussing in person. The 13th international congress on autoimmunity 2022 (AUTO13) Athens

While autoimmunity is a branch of medicine linked to every single organ system via direct and indirect pathways, meeting in person to discuss autoimmunity during the 13^th international congress on autoimmunity (AUTO13) with participants from all over the world had a very good reason. The mechanisms involved in autoimmune diseases are of extreme importance and in fact critical in understanding the course of diseases as well as selecting proper therapies. COVID-19 has served as a great example of how autoimmunity is deeply involved in the disease and directly correlated to severity, morbidity, and mortality. For instance, initially the term cytokine storm dominated, then COVID-19 was addressed as the new member of the hyperferritinemic syndrome, and also the use of immunosuppressants in patients with COVID-19 throughout the pandemic, all shed light on the fundamental role of autoimmunity. Unsurprisingly, SARS-CoV-2 was called the “autoimmune virus” during AUTO13. Subsequently, the correlation between autoimmunity and COVID-19 vaccines and post-COVID, all were discussed from different autoimmune aspects during the congress. In addition, updates on the mechanisms of diseases, autoantibodies, novel diagnostics and therapies in regard to autoimmune diseases such as antiphospholipid syndrome, systemic lupus erythematosus, systemic sclerosis and others, were discussed in dedicated sessions. Due to the magnificence of the topics discussed, we aimed to bring in our article hereby, the pearls of AUTO13 in terms of updates, new aspects of autoimmunity, and interesting findings. While more than 500 abstract were presented, concluding all the topics was not in reach, hence major findings were summarized.

The Role of Intravitreal Corticosteroids in the Treatment of DME: Predictive OCT Biomarkers

This work aims to summarize predictive biomarkers to guide treatment choice in DME. Intravitreal anti-VEGF is considered the gold standard treatment for centers involving DME, while intravitreal steroid treatment has been established as a second-line treatment in DME. However, more than 1/3 of the patients do not adequately respond to anti-VEGF treatment despite up to 4-weekly injections. Not surprisingly, insufficient response to anti-VEGF therapy has been linked to low-normal VEGF levels in the serum and aqueous humor. These patients may well benefit from an early switch to intravitreal steroid treatment. In these patients, morphological biomarkers visible in OCT may predict treatment response and guide treatment decisions. Namely, the presence of a large amount of retinal and choroidal hyperreflective foci, disruption of the outer retinal layers and other signs of chronicity such as intraretinal cysts extending into the outer retina and a lower choroidal vascular index are all signs suggestive of a favorable treatment response of steroids compared to anti-VEGF. This paper summarizes predictive biomarkers in DME in order to assist individual treatment decisions in DME. These markers will help to identify DME patients who may benefit from primary dexamethasone treatment or an early switch.

Autoimmune gastrointestinal dysmotility following SARS-CoV-2 infection successfully treated with intravenous immunoglobulin

BACKGROUND

Autoimmune gastrointestinal dysmotility (AGID) is a limited form of dysautonomia that can be paraneoplastic or idiopathic. Some presentations can be preceded by a viral infection.

METHODS

We report a case of a 17-year-old girl that developed intractable nausea and early satiety after SARS-CoV-2 infection.

KEY RESULTS

Over ten months, she required nasogastric and nasoduodenal tube feedings and finally was advanced to total parenteral nutrition to meet her caloric needs. Her α3 nicotinic ganglionic acetylcholine and anti-striational antibodies were mildly elevated. Gastrointestinal transit scintigraphy studies showed delayed gastric emptying and slowed small bowel transit. Thermoregulatory sweat test showed areas of anhidrosis consistent with autonomic sudomotor impairment. After IVIG treatment the patient's symptoms improved dramatically and she was able to tolerate full oral diet. This was reflected by improvement of her baseline transit studies and the thermoregulatory sweat test.

CONCLUSIONS AND INFERENCES

This is the first report of AGID occurring after SARS-CoV-2 infection. The dramatic response to IVIG emphasizes the importance of early recognition and the reversible and treatable nature of this condition.

Novel Cell-Based Assay for Alpha-3 Nicotinic Receptor Antibodies Detects Antibodies Exclusively in Autoimmune Autonomic Ganglionopathy

Background and Objectives

Autoantibodies against α3-subunit–containing nicotinic acetylcholine receptors (α3-nAChRs), usually measured by radioimmunoprecipitation assay (RIPA), are detected in patients with autoimmune autonomic ganglionopathy (AAG). However, low α3-nAChR antibody levels are frequently detected in other neurologic diseases with questionable significance. Our objective was to develop a method for the selective detection of the potentially pathogenic α3-nAChR antibodies, seemingly present only in patients with AAG.

Methods

The study involved sera from 55 patients from Greece, suspected for autonomic failure, and 13 patients from Italy diagnosed with autonomic failure, positive for α3-nAChR antibodies by RIPA. In addition, sera from 52 patients with Ca²⁺ channel or Hu antibodies and from 2,628 controls with various neuroimmune diseases were included. A sensitive live cell-based assay (CBA) with α3-nAChR–transfected cells was developed to detect antibodies against the cell-exposed α3-nAChR domain.

Results

Twenty-five patients were found α3-nAChR antibody positive by RIPA. Fifteen of 25 patients were also CBA positive. Of interest, all 15 CBA-positive patients had AAG, whereas all 10 CBA-negative patients had other neurologic diseases. RIPA antibody levels of the CBA-negative sera were low, although our CBA could detect dilutions of AAG sera corresponding to equally low RIPA antibody levels. No serum bound to control-transfected cells, and none of the 2,628 controls was α3-CBA positive.

Discussion

This study showed that in contrast to the established RIPA for α3-nAChR antibodies, which at low levels is of moderate disease specificity, our CBA seems AAG specific, while at least equally sensitive with the RIPA. This study provides Class II evidence that α3-nAChR CBA is a specific assay for AAG.

Classification of Evidence

This study provides Class II evidence that an α3-nAChR cell-based assay is a more specific assay for AAG than the standard RIPA.

Autoantibodies from patients with complex regional pain syndrome (CRPS) induce pro-inflammatory effects and functional disturbances on endothelial cells in vitro

ABSTRACT

Complex regional pain syndrome (CRPS) is an inadequate local response after a limb trauma, which leads to severe pain and autonomic and trophic changes of the affected limb. Autoantibodies directed against human β2 adrenergic and muscarinic M2-receptors (hβ2AR and hM2R) have been described in CRPS-patients previously.We analyzed sera from CRPS-patients for autoantibodies against hß2AR, hM2R and endothelial cells, and investigated the functional effects of purified IgG, derived from 13 CRPS patients, on endothelial cells. Eleven healthy controls, seven radial fracture patients without CRPS, and 10 patients with peripheral arterial vascular disease served as controls.CRPS-IgG, but not control IgG, bound to the surface of endothelial cells (P < 0.001) and to hβ2AR and hM2R (P < 0.05), the latter being reversed by adding β2AR and M2R antagonists. CRPS-IgG led to an increased cytotoxicity and a reduced proliferation rate of endothelial cells, and by adding specific antagonists, the effect was neutralized. Regarding second messenger pathways, CRPS-IgG induced ERK-1/2-, P38-, and STAT1-phosphorylation, while AKT-phosphorylation was decreased at the protein level. In addition, increased expression of adhesion molecules (ICAM-1, VCAM-1) on the mRNA-level was induced by CRPS-IgG, thus inducing a pro-inflammatory condition of the endothelial cells.Our results show that patients with CRPS not only develop autoantibodies against hβ2AR and hM2R, but these antibodies interfere with endothelial cells, inducing functional effects on these in vitro, and thus might contribute to the pathophysiology of CRPS.

Subunit-specific autoantibodies in autoimmune autonomic ganglionopathy

Autoimmune Autonomic Ganglionopathy (AAG) is a disorder that causes autonomic failure and is associated with alpha3-ganglionic acetylcholine-receptor (gnACHR) antibodies. Assays that detect antibodies to whole gnACHR or subunits are available. We compared in-house subunit-specific immunoassays using bacterially-expressed alpha3 and beta4 subunits against an immunomodulation assay to detect antibodies in patients with AAG or control groups in a novel 2-step clinical-characteristic unblinding protocol. Only 1/8 patients with seropositive-AAG had subunit-specific antibodies, with sensitivity, specificity, false-negative and positive rates of 12.5, 85.2, 78.6 and 13.4% respectively. Subunit-specific antibody-derived false-positive results can lead to misdiagnosis, as autonomic failure is not specific to AAG.

Case Report: Opsoclonus-Myoclonus Syndrome Associated With Contactin-Associated Protein-Like 2 and Acetylcholine Receptor Autoantibodies in the Setting of Non-Small Cell Lung Carcinoma

Opsoclonus myoclonus syndrome (OMS) is a rare immune-mediated paraneoplastic or para/-post-infectious syndrome characterized by "dancing" eye movements, myoclonus, and ataxia. Neuropsychiatric symptoms have also been reported. Without treatment, OMS may progress to further neurological impairment and even death. Autoimmune attack of CNS structures in OMS is most commonly mediated by anti-Ri (also known as ANNA2) IgG antibodies, with additional findings implicating antibodies targeting various neurotransmitter receptors. Prompt immunotherapy and neoplasm treatment may result in improvement. We report a novel association of Contactin-Associated Protein-Like 2 (Caspr2) antibodies occurring in association with paraneoplastic OMS. While breast cancer and small cell lung cancer (SCLC) are more commonly associated with OMS among adults, we characterize a novel association between Caspr2 antibody in a patient with mixed non-small cell and small cell lung carcinoma.

Autoimmune autonomic ganglionopathy: Ganglionic acetylcholine receptor autoantibodies

Autoimmune Autonomic Ganglionopathy (AAG) is a rare immune-mediated disease of the autonomic nervous system. The incidence of AAG is unknown and diagnosis is often difficult due to the multicompartmental nature of the autonomic nervous system - sympathetic, parasympathetic and enteric components - with variable severity and number of components affected. Diagnostic confidence is increased when ganglionic acetylcholine receptor (gnACHR) autoantibodies are detected. Three gnACHR autoantibody diagnostic assays have been described (two binding assays, one receptor immunomodulation assay), but cross-validation between assays is limited. The prevalence of gnACHR autoantibodies in AAG is not known, with application of different clinical and laboratory criteria in the few studies of AAG cohorts and large retrospective laboratory studies of positive gnACHR autoantibodies lacking adequate clinical characterisation. Furthermore, the rate of unexpected gnACHR autoantibody positivity in conditions without overt autonomic dysfunction (false positive results) adds to the complexity of their interpretation. We review the pathophysiology of gnACHR autoantibodies and assays for their detection, with immunomodulation and high titer radioimmunoprecipitation results likely offering better AAG disease identification.

[Acute-onset autoimmune autonomic ganglionopathy remarkably effective in intravenous high-dose immunoglobulin therapy]

A 77-year-old woman developed acute onset of orthostatic hypotension, urinary retention, and constipation. Neurological examination on admission showed severe orthostatic hypotension accompanied by syncope, mydriatic pupils, and attenuation of light reflexes with no abnormalities in other neurological systems. Autonomic testing revealed denervation hypersensitivity in norepinephrine (NE) intravenous infusion test and 0.125% pilocarpine instillation test, low NE in the serum, and decreased amount of sweating in quantitative sudomotor axon reflex test. These findings indicated dysfunction of postganglionic autonomic nerves. Autoimmune autonomic ganglionopathy (AAG) was diagnosed due to the presence of anti-ganglionic acetylcholine receptors. The patient was given intravenous high-dose immunoglobulin therapy (IVIg), improving orthostatic hypotension, urinary retention, and constipation. Previous reports indicated that the response to IVIg varied from case to case. Thus, this case suggests that IVIg is effective in acute-onset AAG cases.

Cutaneous manifestations of orthostatic intolerance syndromes

Dysautonomia refers to a group of autonomic nervous system disorders that affect nearly 70 million people worldwide. One subset of dysautonomia includes syndromes of orthostatic intolerance (OI), which primarily affect adolescents and women of childbearing age. Due to the variability in disease presentation, the average time from symptom onset to diagnosis of dysautonomia is 6 years. In general, there is a paucity of dermatological research articles describing patients with dysautonomia. The objective of this review is to summarize the existing literature on cutaneous manifestations in dysautonomia, with an emphasis on syndromes of OI. A PubMed database of the English-language literature (1970–2020) was searched using the terms “dysautonomia”, “orthostatic intolerance”, “cutaneous”, “skin”, “hyperhidrosis”, “hypohidrosis”, “sweat”, and other synonyms. Results showed that cutaneous manifestations of orthostatic intolerance are common and varied, with one paper citing up to 85% of patients with OI having at least one cutaneous symptom. Recognition of dermatological complaints may lead to an earlier diagnosis of orthostatic intolerance, as well as other comorbid conditions.

Parkinsonism in viral, paraneoplastic, and autoimmune diseases

Secondary parkinsonism, namely parkinsonism due to causes other than idiopathic neurodegeneration, may have multiple etiologies. Common secondary etiologies of parkinsonism such as drug-induced or vascular etiologies are well documented. Other secondary causes of parkinsonism such as infectious (mainly viral and prion-like diseases), autoimmune (systemic/drug-induced) and paraneoplastic etiologies are rare but are a topic of increasing interest. Older examples from the existing literature demonstrate the intricacies of viral infection from the last pandemic of the 20th century on the development of hypokinetic symptoms experienced in post-encephalitic patients. Viral and prion-like infections are only part of a complex interplay between the body's immune response and aberrant cell cycle perturbations leading to malignancy. In addition to the classic systemic autoimmune diseases (mainly systemic lupus erythematosus - SLE, and Sjögren syndrome), there have been new developments in the context of the current COVID-19 pandemic as well as more prominent use of immunotherapies such as immune checkpoint inhibitors in the treatment of solid tumors. Both of these developments have deepened our understanding of the underlying pathophysiologic process. Increased awareness and understanding of these rarer etiologies of parkinsonism is crucial to the modern diagnostic evaluation of a patient with parkinsonian symptoms as the potential treatment options may differ from the conventional levodopa-based therapeutic regimen of idiopathic Parkinson's disease. This review article aims to give an up-to-date review of the current literature on parkinsonian symptoms, their pathogenesis, diagnostic methods, and available treatment options. Many potential future directions in the field of parkinsonian conditions remain to be explored. This article is part of the Special Issue "Parkinsonism across the spectrum of movement disorders and beyond" edited by Joseph Jankovic, Daniel D. Truong and Matteo Bologna.

A review of cardiac autonomics: from pathophysiology to therapy

The effective management of cardiovascular diseases requires knowledge of intrinsic and extrinsic innervation of the heart and an understanding of how perturbations of said components affect cardiac function. The innate cardiac conduction system, which begins with cardiac pacemaker cells and terminates with subendocardial Purkinje fibers, is modulated by said systems. The intrinsic component of the cardiac autonomic nervous system, which remains incompletely elucidated, consists of intracardiac ganglia and interconnecting neurons that tightly regulate cardiac electrical activity. Extrinsic components of the autonomic nervous system, such as carotid baroreceptors and renin-angiotensin-aldosterone system, modulate sympathetic input to the heart through the stellate ganglion and parasympathetic input via the vagus nerve. There remains a need for additional therapies to treat conditions, such as advanced heart failure and refractory arrhythmias, and a better understanding of autonomics may be key to their development.

Ganglionic Acetylcholine Receptor Antibodies in Postural Tachycardia Syndrome

Objective

Postural tachycardia syndrome (POTS), the most common form of dysautonomia, may be associated with autoimmunity in some cases. Autoantibodies against the ganglionic acetylcholine receptor (gAChR) have been reported in a minority of patients with POTS, but the prevalence and clinical relevance is unclear.

Methods

Clinical information and serum samples were systematically collected from participants with POTS and healthy control volunteers (n = 294). The level of positive gAChR antibodies was classified as very low (0.02-0.05 nmol/L), low (0.05-0.2 nmol/L), and high (>0.2 nmol/L).

Results

Fifteen of 217 patients with POTS (7%) had gAChR antibodies (8 very low and 7 low). Six of the 77 healthy controls (8%) were positive (3 very low and 3 low). There were no clinical differences between seropositive and seronegative patients with POTS.

Conclusions

Prevalence of gAChR antibody did not differ between POTS and healthy controls, and none had high antibody levels. Patients with POTS were not clinically different based on seropositivity. Low levels of gAChR antibodies are not clinically important in POTS.

Evaluation of commercially available antibodies and fluorescent conotoxins for the detection of surface ganglionic acetylcholine receptor on the neuroblastoma cell line, IMR-32 by flow cytometry

Commercially available antibodies that bind to the human muscle acetylcholine receptor (ACHR) have been validated previously for flow cytometric use (Keefe et al., 2009; Leite et al., 2008; Lozier et al., 2015). Despite a multitude of commercially available antibodies to other nicotinic ACHRs, validation in a wide variety of immunoassay formats is lacking; when studied, a large proportion of these antibodies have been deemed not fit for most research purposes (Garg and Loring, 2017). We have recently described a flow cytometric immunomodulation assay for the diagnosis of Autoimmune Autonomic Ganglionopathy (AAG) (Urriola et al., 2021) that utilises the monoclonal antibody mab35(Urriola et al., 2021) which is specific for ganglionic ACHR (gnACHR) that contain α3 subunits (Vernino et al., 1998). Other fluorescent ligands for α3-gnACHR have not been validated for flow cytometric use. We investigated 7 commercially sourced antibodies and 3 synthetic fluorescent novel conotoxins purported to specifically bind to the extracellular domains of the gnACHR, and compared the results to staining by mab35, using flow cytometry with the neuroblastoma cell line IMR-32. We also evaluated the degree of non-specific binding by depleting the cell membrane of the relevant acetylcholine receptor with a pre-incubation step involving the serum from a patient with Autoimmune Autonomic Ganglionopathy containing pathogenic antibodies to the ganglionic acetylcholine receptor. None of the assessed conotoxins, and only one antibody (mab35) was found to perform adequately in flow cytometric staining of the native ganglionic acetylcholine receptor.

Postural orthostatic tachycardia syndrome (POTS) occurring during treatment for breast cancer

Postural orthostatic tachycardia syndrome (POTS) is a common condition of orthostatic intolerance in response to changes in position. We report a case of a middle-aged woman presenting with a new onset of POTS likely due to chemotherapy for treatment of breast cancer. She was started on a trial of a beta blocker, which was effective in controlling her symptoms and heart rate. The objective of this report was to encourage clinicians to consider POTS as a differential diagnosis, while managing patients with symptoms of orthostatic intolerance.