Distal myasthenia gravis and sensory neuronopathy with anti-50 kDa antibody mimicking sensory-motor neuropathy.

Bilateral foot drop, paraesthesiae, and absent tendon reflexes in the lower limbs are, for the clinical neurologist, the hallmarks of a duration dependent sensory-motor neuropathy. We report a patient in which this clinical picture was sustained by the combination of an atypical distal presentation of myasthenia gravis with a probable immunomediated sensory neuronopathy. A 69 year old woman presented with a three month history of progressive walking difficulties and paraesthesiae in the lower limbs. Examination showed bilateral foot drop with pronounced weakness of the tibioperoneal muscles (MRC= 2) and posterior leg muscles (MRC= 3), slight weakness in arm abduction (MRC=4+), tactile and pain distal sensory loss, and absent tendon jerks in the lower limbs. There were no oculobulbar symptoms and signs nor ataxia. Motor conduction velocities and compound muscle action potential (CMAP) amplitudes were normal (ulnar= 57 m/s, 9.7 mV; peroneal= 44 m/s, 3.9 mV). Sensory conduction velocities were slowed with reduced amplitude sensory nerve potentials (ulnar=44 m/s, 5 μV; sural= 30.6 m/s, 1.8 μV). H reflexes were absent with normal latency F responses. Tibialis anterior muscle EMG did not show spontaneous activity and recruitment was full but during prolonged maximal voluntary activation there was a pronounced reduction of the interferential pattern amplitude. Quantitative motor unit …