P-NE013. Distal myasthenia gravis – A missed clinical diagnosis

Introduction. What is well known: Myasthenia gravis presents with ocular, bulbar and proximal limb weakness. What is less known: Myasthenia gravis can rarely present with predominant distal weakness of hand muscles. Myasthenia gravis (MG) is an immune mediated, post-synaptic neuromuscular transmission disorder, presenting with predominant ocular, bulbar and/or proximal fluctuating weakness and fatiguability. Distal and asymmetric onset of symptoms in MG is rare and could lead to delay in diagnosis especially when fatiguability or fluctuation is not clearly reported as a prominent initial symptom - as seen in our patients. Results. We report 3 cases of distal MG who presented with predominant distal asymmetric hand weakness. Their clinically diagnoses for referral to the electrodiagnostic (EDx) laboratory were chronic inflammatory demyelinating polyneuropathy, C8T1 motor radiculopathy and multifocal motor neuropathy. It was in the EDx laboratory that the diagnosis of MG was suspected in these patients. Since the routine EDx tests were normal in all 3 patients - a repetitive nerve stimulation test (RNST) was done - which was positive in the affected muscles and hence a diagnosis of distal MG made (This is the protocol followed in our laboratory). These patients were then found to have high serum levels of antibodies to acetylcholine receptors - confirming the diagnosis of MG. RNST is not routinely done in all patients sent for electrodiagnostic testing and none of these patients had a reference for the same – however using a protocol based method of EDx testing, leading to the diagnosis of a treatable condition. Conclusion. Electrodiagnosticians need to be aware of this presentation of MG and follow protocols or else the diagnosis could be missed.