PET evidence of central GABAergic changes in stiff-person syndrome

Psychiatric Symptoms in Stiff-Person Syndrome: A Systematic Review and a Report of Two Cases

BACKGROUND

The clinical spectrum of stiff-person syndrome (SPS) encompasses a wide range of signs including psychiatric symptoms (PS).

OBJECTIVE

Our objective was to provide an overview of the spectrum of PS in SPS through a systematic literature search and 2 illustrative case reports.

METHODS

We reported 2 anti-glutamic acid decarboxylase-positive SPS cases that presented with phobic disorder, and we performed a systematic review by following the 2020 Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Articles published in PubMed, MEDLINE on Ovid, Embase, and via a manual search before October 20, 2020, were selected by 2 independent reviewers. Original studies, case reports, editorials, commentaries, and letters to the editor reporting cases of SPS with PS were all included. Conference abstracts, reviews and book chapters, unavailable articles, and those not reporting SPS cases or PS were excluded. Quantitative summary data were calculated.

RESULTS

In addition to our 2 cases, we identified 237 cases of SPS with PS from 74 additional included publications totaling 239 patients. Anxiety (56%) and depression (45%) were the most common PS in SPS. Mean diagnostic delay was 4.7 years. Among the 3 SPS phenotypes, the classic form was predominant (77%), followed by stiff-limb syndrome (13%) and progressive encephalomyelitis with rigidity and myoclonus (10%). The most frequent etiology of SPS with PS was autoimmune (90%), followed by cryptogenic (7%) and paraneoplastic forms (7%). These patients were mainly treated with immune-mediated therapies and GABAergic drugs.

CONCLUSIONS

Our review revealed that the most common PS of SPS are anxiety and depression occurring mostly in autoimmune and classic forms, allowing a clearer understanding of this entity, which may lead to earlier diagnosis and better outcome.

Stiff Person Syndrome and Type 1 Diabetes Mellitus: a Case of the Chicken or the Egg?

Anti-glutamic acid decarboxylase (anti-GAD) antibodies are linked with both autoimmune diabetes and the rare neurological disorder stiff person syndrome (SPS). SPS is an uncommon autoimmune-mediated condition characterized by painful episodic spasms and progressive muscle rigidity. We present the case of a 23-year-old non-diabetic, insulin-naïve woman with known SPS who was hospitalized for SPS-related symptomatology. The patient quickly developed type 1 diabetes mellitus (T1DM) with unexpectedly large insulin requirements. To our knowledge, there are no other reports describing rapid T1DM development during an acute hospitalization for SPS and fewer than 5 case reports describing the association of SPS with extreme insulin resistance. Our case highlights the key clinical features, pathology, and pathogenesis of both SPS and T1DM and explores the relationship between the two disease processes.

Cerebellar disease associated with anti-glutamic acid decarboxylase antibodies: review

Several neurological syndromes have been recognized associated to GAD antibodies. Among those disorders, cerebellar ataxia (CA) is one of the most common, along with stiff-person syndrome. Patients with GAD associated CA present with a progressive pancerebellar syndrome, with a subacute or chronic evolution, along with other neurological manifestations such as stiffness, oculomotor dysfunction, epilepsy, and cognitive dysfunction. These symptoms may be preceded by the so-called "brainstem attacks", where manifestations consistent with transient dysfunction of the brainstem may be observed. These patients frequently have extra-neurologic autoimmune manifestations such as diabetes mellitus type 1, polyendocrine autoimmune syndrome, pernicious anemia, vitiligo, etc. A proportion of patients may present with an underlying neoplasia, but the course is less aggressive than in those patients with classical paraneoplastic CA with onconeural antibodies. The diagnosis is based on the present of high serum and CSF titers of GAD antibodies, with intrathecal production of such antibodies. Treatment is aimed to decrease the immunological response with intravenous immunoglobulin, steroids, rituximab and oral immunosuppressive drugs. A subacute presentation and rapid initiation of immunotherapy seem to be the predictors of a favorable clinical response.

Spinal-generated movement disorders: a clinical review

Spinal-generated movement disorders (SGMDs) include spinal segmental myoclonus, propriospinal myoclonus, orthostatic tremor, secondary paroxysmal dyskinesias, stiff person syndrome and its variants, movements in brain death, and painful legs-moving toes syndrome. In this paper, we review the relevant anatomy and physiology of SGMDs, characterize and demonstrate their clinical features, and present a practical approach to the diagnosis and management of these unusual disorders.

Stiff-person syndrome: insights into a complex autoimmune disorder

Stiff-person syndrome (SPS) is characterised by progressive rigidity and muscle spasms affecting the axial and limb muscles. Since its initial description in 1956, marked progress has been made in the clinical characterisation, understanding of pathogenesis and therapy of this disorder. SPS can be classified according to the clinical presentation into classic SPS and SPS variants: focal or segmental-SPS, jerking-SPS and progressive encephalomyelitis with rigidity and myoclonus. Most patients with SPS have antibodies directed against the glutamic acid decarboxylase, the rate-limiting enzyme for the production of the inhibitory neurotransmitter γ-aminobutyric acid (GABA). Antibodies directed against GABA(A) receptor-associated protein, and the glycine-α1 receptor can also be observed. Paraneoplastic SPS is commonly associated with antiamphiphysin antibodies and breast cancer. Treatment of SPS with drugs that increase the GABAergic tone combined with immunotherapy can improve the neurological manifestations of these patients. The prognosis, however, is unpredictable and spontaneous remissions are unlikely.

Paraneoplastic immune-mediated neurological effects of systemic cancers

Cancer patients may develop paraneoplastic neurological conditions associated with autoantibodies directed against neural or neuromuscular tissues. These syndromes are frequently manifested in advance of the cancer presentation by several months or years necessitating a detailed and expensive investigation to search for the presence of a malignancy. In such cases additional assistance may be obtained by the early employment of whole body 18F flurodeoxyglucose positron emission tomography as a cancer screening imaging procedure for early cancer diagnosis and potential therapy. Effective therapy of the primary cancer consists the best current therapy for a given paraneoplastic syndrome. However, other forms of immune modulation, such as plasma exchange, intravenous gamma globulin, other immune therapies and symptomatic treatment for certain PNS may have additional benefit.

GABA-A receptor impairment in cerebellar ataxia with anti-glutamic acid decarboxylase antibodies

Antibodies against glutamic acid decarboxylase (GAD-Abs) are associated with cerebellar ataxia, which is refractory to treatment with GABAergic drugs. To investigate the GABAergic neuronal system in vivo, we performed a combined positron emission tomography (PET) study with [(11)C]-flumazenil and [(18)F]-fluorodeoxyglucose (FDG) in three patients with cerebellar ataxia with GAD-Abs. The GABA-A receptor function was investigated using flumazenil, which is a selective GABA-A receptor ligand, while FDG-PET using a three-dimensional stereotactic surface projection analysis was performed to estimate the metabolic rates of glucose (MRGlc) in the patients. GABAergic drugs showed no efficacy for the cerebellar ataxia in all three patients, and all three displayed a significant decrease in flumazenil binding in the cerebellum. No MRGlc decrease in the cerebellum was found in the two patients who presented with amelioration of cerebellar ataxia following intravenous immunoglobulin (IVIG) therapy, whereas a significant MRGlc decrease in the cerebellar hemisphere was observed in another patient who showed severe cerebellar atrophy on magnetic resonance images and no response to the IVIG therapy. The decreased flumazenil binding in the present patients indicated cerebellar GABA-A receptor impairment, which may be due to either neuronal cell loss, as demonstrated by the decreased MRGlc, or a dysfunction in GABAergic neuronal inhibition. Although GAD-Abs have been postulated to prevent the synthesis of GABA, resulting in decreased GABAergic transmission, the GABA-A receptor impairment may play another pathogenic role in cerebellar ataxia associated with GAD-Abs resulting in a condition refractory to GABAergic drug therapy.

Human Stiff person syndrome IgG-containing high-titer anti-GAD65 autoantibodies induce motor dysfunction in rats

Stiff person syndrome (SPS) is an autoimmune CNS disorder characterized by muscle rigidity, spasms and anxiety. The majority of patients have high-titer autoantibodies (ab) against glutamate decarboxylase (GAD65). A pathogenic role of SPS-associated IgG with ab against GAD65 has been shown for anxiety-like behavior but not for the core motor signs. We repetitively injected the purified IgG fraction of an SPS patient with severe motor impairment but without anxious comorbidity containing high titers of anti-GAD65 ab (SPS-IgG) into the lateral ventricle (i.c.v.) or intrathecally (i.th.) at the spinal level in experimental rats. We analyzed the effects on motor and anxiety-like behavior. Non-SPS human IgG fractions served as controls. Animals injected i.c.v. with SPS-IgG showed stiffness-like behavior with impaired walking ability and reduced grip strength of the upper limbs as well as postural and sensorimotor dysfunction. Testing for anxiety-like behavior revealed no significant differences between SPS and control IgG-treated rats. IgG deposits were found only in rats treated with SPS-IgG and were localized predominantly in CNS structures involved in motor control including globus pallidus, internal capsule, striatum and anterior thalamus. Double immunofluorescence staining revealed that predominantly GABAergic interneurons were positive for i.c.v. injected SPS-IgG. Rats injected i.th. with SPS-IgG did not present obvious motor symptoms and had a normal synaptic transmission at the spinal level. We conclude that SPS-like motor dysfunction can be induced in rats by passive transfer of IgG from an SPS-patient with high titer of anti-GAD65 ab. GABAergic dysfunction in supraspinal motor pathways rather than in the spinal cord may lead to motor deficits observed in the rats contrasting observations made in SPS with amphiphysin antibodies.

Stiff person syndrome: advances in pathogenesis and therapeutic interventions

Stiff person syndrome (SPS) varies from mild to severe, but if untreated it can be progressive and disabling. Although progress has been made in understanding and treating SPS, the disease remains underdiagnosed, delaying treatment. Antibodies against glutamic acid decarboxylase provide an excellent diagnostic marker, but their role in disease pathogenesis is uncertain. Research focused on identifying new autoantigens has provided evidence that gamma-aminobutyric acid (GABA)(A) receptor-associated protein (GABARAP), a 14-kD protein localized at the postsynaptic regions of GABAergic synapses, is an antigenic target. Circulating anti-GABARAP antibodies that inhibit GABA(A) receptor expression on GABAergic neurons have been found in up to 65% of SPS patients. The impairment of GABAergic pathways and reduction of brain GABA results in clinical manifestations of stiffness, spasms, and phobias. Increased awareness of SPS among practicing physicians is necessary to recognize the disease early and prevent permanent disability. Most patients with SPS respond to GABA-enhancing drugs, but the high doses required cause unacceptable adverse effects. The disease clearly responds to intravenous immunoglobulin, but repeated infusions are needed to maintain response. New immunomodulating agents are being explored to treat difficult cases and to induce long-lasting remissions.

Human stiff-person syndrome IgG induces anxious behavior in rats

Background

Anxiety is a heterogeneous behavioral domain playing a role in a variety of neuropsychiatric diseases. While anxiety is the cardinal symptom in disorders such as panic disorder, co-morbid anxious behavior can occur in a variety of diseases. Stiff person syndrome (SPS) is a CNS disorder characterized by increased muscle tone and prominent agoraphobia and anxiety. Most patients have high-titer antibodies against glutamate decarboxylase (GAD) 65. The pathogenic role of these autoantibodies is unclear.

Methodology/Principal Findings

We re-investigated a 53 year old woman with SPS and profound anxiety for GABA-A receptor binding in the amygdala with (11)C-flumazenil PET scan and studied the potential pathogenic role of purified IgG from her plasma filtrates containing high-titer antibodies against GAD 65. We passively transferred the IgG fraction intrathecally into rats and analyzed the effects using behavioral and in vivo electrophysiological methods. In cell culture, we measured the effect of patient IgG on GABA release from hippocampal neurons. Repetitive intrathecal application of purified patient IgG in rats resulted in an anxious phenotype resembling the core symptoms of the patient. Patient IgG selectively bound to rat amygdala, hippocampus, and frontal cortical areas. In cultured rat hippocampal neurons, patient IgG inhibited GABA release. In line with these experimental results, the GABA-A receptor binding potential was reduced in the patient's amygdala/hippocampus complex. No motor abnormalities were found in recipient rats.

Conclusion/Significance

The observations in rats after passive transfer lead us to propose that anxiety-like behavior can be induced in rats by passive transfer of IgG from a SPS patient positive for anti-GAD 65 antibodies. Anxiety, in this case, thus may be an antibody-mediated phenomenon with consecutive disturbance of GABAergic signaling in the amygdala region.

Advances in the pathogenesis and treatment of patients with stiff person syndrome

Advances in the clinical diagnosis, prognosis, pathogenesis, and therapies for stiff person syndrome (SPS), based on observations in more than 50 consecutive patients, are presented. The syndrome varies from mild to severe, but if untreated it can be progressive and disabling. SPS remains a largely underdiagnosed condition. Anti-glutamic acid decarboxylase (GAD) antibodies provide an excellent diagnostic marker, but their role in disease pathogenesis is uncertain. Research focused on identifying new autoantigens has provided evidence that gamma-aminobutyric acid (GABA)(A) receptor-associated protein (GABARAP), a 14-kD protein localized at the postsynaptic regions of GABAergic synapses, is a new antigenic target. In up to 65% of SPS patients, there are circulating anti-GABARAP antibodies that inhibit the GABA(A) receptor expression on GABAergic neurons. This review examines the diagnostic criteria for SPS, SPS variants, common errors in diagnosis, and a step-by-step therapeutic approach, including new advances in therapy.