Rapidly progressive polymyositis with elevated antiacetylcholine receptor antibody activity

Clinical features of myasthenia gravis with neurological and systemic autoimmune diseases

Multiple reports on the co-existence of autoimmune diseases and myasthenia gravis (MG) have raised considerable concern. Therefore, we reviewed autoimmune diseases in MG to explore their clinical presentations and determine whether the presence of autoimmune diseases affects the disease severity and treatment strategies for MG. We reviewed all the major immune-mediated coexisting autoimmune conditions associated with MG. PubMed, Embase and Web of Science were searched for relevant studies from their inception to January 2023. There is a higher frequency of concomitant autoimmune diseases in patients with MG than in the general population with a marked risk in women. Most autoimmune comorbidities are linked to AChR-MG; however, there are few reports of MuSK-MG. Thyroid disorders, systemic lupus erythematosus, and vitiligo are the most common system autoimmune diseases associated with MG. In addition, MG can coexist with neurological autoimmune diseases, such as neuromyelitis optica (NMO), inflammatory myopathy (IM), multiple sclerosis (MS), and autoimmune encephalitis (AE), with NMO being the most common. Autoimmune diseases appear to develop more often in early-onset MG (EOMG). MS coexists more commonly with EOMG, while IM coexists with LOMG. In addition, MG complicated by autoimmune diseases tends to have mild clinical manifestations, and the coexistence of autoimmune diseases does not influence the clinical course of MG. The clinical course of neurological autoimmune diseases is typically severe. Autoimmune diseases occur most often after MG or as a combined abnormality; therefore, timely thymectomy followed by immunotherapy could be effective. In addition, thymoma-associated AChR MG is associated with an increased risk of AE and IM, whereas NMO and MS are associated with thymic hyperplasia. The co-occurrence of MG and autoimmune diseases could be attributed to similar immunological mechanisms with different targets and common genetic factor predisposition. This review provides evidence of the association between MG and several comorbid autoimmune diseases.

Granulomatous Myositis Associated With Acetylcholine Receptor Antibodies Without Clinical Myasthenia

ABSTRACT

Myasthenia gravis associated with concurrent inflammatory myopathy is a rare but well-described syndrome, most often seen in patients with thymoma. We present a case of biopsy-proven granulomatous myositis associated with positive acetylcholine receptor binding, blocking, and modulating and antistriated antibodies, without clear clinical symptoms of myasthenia gravis and in the absence of thymoma. In addition, we include rarely reported neuromuscular ultrasound findings of granulomatous myositis in a patient without sarcoidosis. Inflammatory myopathy may precede development of myasthenia gravis in myasthenia gravis associated with concurrent inflammatory myopathy, and it is important to remain vigilant for symptoms suggestive of myasthenia gravis, especially in the presence of positive myasthenia-associated antibodies.

Inflammatory myopathy with myasthenia gravis: Thymoma association and polymyositis pathology

Objective

To provide evidence that idiopathic inflammatory myopathy (IM) with myasthenia gravis (MG) frequently shows thymoma association and polymyositis (PM) pathology and shares clinicopathologic characteristics with IM induced by immune checkpoint inhibitors (ICIs).

Methods

We analyzed the clinicopathologic features of 10 patients with idiopathic IM and MG identified in 970 consecutive patients with biopsy-proven IM.

Results

Seven patients (70%) had thymoma. IM and MG were diagnosed with more than 5-year time difference in 6 thymomatous patients and within 1 year in 1 thymomatous and 3 nonthymomatous patients. Seven thymomatous patients showed rhabdomyolysis-like features with respiratory failure (4/7), dropped head (3/7), cardiac involvement (2/7), and positive anti-acetylcholine receptor (anti-AChR) and anti-titin antibodies (7/7 and 4/6, respectively) but rarely showed ocular symptoms (2/7) or decremental repetitive nerve stimulation (RNS) responses (1/7) at IM diagnosis. Three nonthymomatous patients showed acute cardiorespiratory failure with rhabdomyolysis-like features (1/3), positive anti-AChR and anti-titin antibodies (3/2 and 2/2, respectively), and fluctuating weakness of the skeletal muscle without ocular symptoms (3/3). Muscle pathology showed a PM pathology with infiltration of CD8-positive CD45RA-negative T-lymphocytes (9/9), scattered endomysial programmed cell death 1 (PD-1)-positive cells (9/9), and overexpression of programmed cell death ligand 1 (PD-L1) on the sarcolemma of muscle fibers around the infiltrating PD-1-positive cells (7/9).

Conclusion

Rhabdomyolysis-like features, positive anti-AChR antibody without decremental RNS responses, and PD-L1 overexpression are possible characteristics shared by ICI-induced IM. Frequent thymoma association in patients with idiopathic IM and MG may suggest thymoma-related immunopathogenic mechanisms, including dysregulation of the immune checkpoint pathway.

Reversible spontaneous EMG activity during myasthenic crisis: Two case reports

Background

Myasthenia Gravis (MG) is an antibody-mediated autoimmune neuromuscular disorder, clinically presenting with fatigable variable muscle weakness. Typical electrodiagnostic findings are a decremental response to repetitive nerve stimulation with post-exercise facilitation, and motor unit instability expressed as increased jitter on single fibre-EMG. Presence of spontaneous activity on standard EMG is traditionally considered inconsistent with a diagnosis of MG and would direct the differential diagnosis towards a primary denervating or usually inflammatory myopathic process.Case reportWe herein present two patients with progressive severe bulbar symptomatology, whose needle-EMG examinations showed spontaneous activity and led to erroneous initial diagnoses of inflammatory myopathy and anterior horn cell disease respectively. Follow-up neurophysiological investigations, positive anti-AchR titres and good response to IVIg and steroids eventually established the diagnosis of Myasthenia Gravis.

Conclusions

Clinically severe Myasthenia Gravis can potentially present with spontaneous activity on EMG, mimicking acute myopathic or neurogenic processes. This can prove particularly perplexing and cause significant delays in the diagnosis and treatment of a myasthenia relapse.

Acetylcholine receptor antibodies in patients with genetic myopathies: clinical and biological significance

We report two patients with facioscapulohumeral muscular dystrophy (FSHD) presenting with atypical clinical features. Both were found to have antibodies to acetylcholine receptor (AChR-abs) and improved with immunosuppression. AChR-abs have also been reported in patients with other genetic myopathies and it is unlikely that the association is coincidental. There is increasing evidence that muscle fibre degeneration can cause innate immune responses (autoinflammation) that may lead to the breaking of immune tolerance and the generation of autoantibodies to muscle proteins. We compare and contrast this process with the pathogenesis of archetypical myasthenia gravis.

Myasthenia Gravis and Hypothyroidism in a Dog With Meningomyelitis

A 12-year-old, spayed female miniature poodle was evaluated because of a 4-day history of paraparesis, dysuria, and tenesmus. Neurological assessment suggested peripheral nervous system dysfunction, predominantly pelvic limb weakness with a possible concurrent sixth lumbar (L6) to second sacral (S2) myelopathy. Further studies supported the diagnoses of myasthenia gravis, hypothyroidism, and meningomyelitis. To the authors’ knowledge, this is the first reported case of concurrent myasthenia gravis and meningomyelitis in the dog. It was unclear whether the identified conditions evolved from a shared etiopathogenesis or were merely coincidental.