[Observation of clinical and electrophysiological features in patients with distal myasthenia gravis]

Objective: To explore the clinical and electrophysiological features and prognosis of distal myasthenia gravis (MG). Methods: Data of MG patients in Beijing Tiantan Hospital from October 2016 to March 2017 were reviewed, including thorough neurological examinations, nerve conduction studies, repetitive nerve stimulations (RNS) and needle electromyographies. Distal MG patients were included and were analyzed as to their clinical and electrophysiological features and response to treatments. Results: Four patients (7.7%) could be classified as distal type among 52 definitely diagnosed MG patients. They had initial symptoms at age 36 to 64 and developed distal limb muscle weakness in the first month to 6 years after the onset of this disease. Hand muscles were preferentially involved in a non-uniform way. And one patient also had leg weakness on his tibialis anterior muscles. RNS showed a more significant decrement at slow rates in distal muscles, compared with proximal muscles. The baseline compound muscle action potentials (CMAP) of the distal affected muscles presented with slightly decreased or fluctuating amplitudes. Their weakness of ocular, bulbar, proximal and distal limb muscles improved generally after administration of acetylcholinesterase inhibitors or steroids plus acetylcholinesterase inhibitors. Electrophysiological reexaminations revealed increased baseline CMAPs, reduced decrement on RNS, and relief of myogenic changes on needle electromyography. Conclusions: Relatively prominent distal limb muscle weakness can be found in a minority of MG patients. Besides profound decrement on slow rate RNS, the involved distal muscles may have a characteristic decreased baseline CMAP, sometimes with a diurnal fluctuation. Distal MG responds well to regular treatments. Its short-term prognosis seems similar to that of common MG with proximal predominance.