| Summary: | 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. Keywords: Myasthenia Gravis, EMG, Spontaneous activity
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