LEMS in the shadow of a hereditary polyneuropathy

Abstract

We draw attention to an instructive instance of the concurrence of an axon-loss sensorimotor polyneuropathy, perhaps an axonal form of Charcot-Marie-Tooth disease (CMT) and Lambert-Eaton myasthenic syndrome (LEMS). This case underscores the principle that electrophysiological exercise testing for facilitation should always be performed, even when an apparently satisfactory explanation exists for diffuse low-amplitude compound muscle action potentials (CMAPs). LEMS is a presynaptic neuromuscular junction disorder characterized by fatigable weakness, areflexia, and variable autonomic dysfunction. 4 Foot deformities, distal weakness and sensory loss, hypo or areflexia, gait dysfunction, and low amplitudes of motor and sensory potentials on nerve conduction study (NCS) are a hallmark of axonal forms of CMT, but LEMS may share several of these features. Recognition of LEMS is important because of its treatability and the potential for an underlying malignancy.Our patient, a 78-year-old man, reported a 16-year history of a "wrapped up and tight" sensation at his feet/ankles, muscle wasting in the legs, and gradually progressive gait difficulty. He complained of chronic and insidious poor endurance with rapid fatigue of his legs when walking, but would feel rejuvenated upon sitting for an hour. He denied positive sensory symptoms, visual disturbance, dizziness upon standing, dry mouth, or dysphagia. He had a history of femoral-popliteal grafts for vascular insufficiency and an elective repair of an abdominal aortic aneurysm. Family history was noncontributory.Examination revealed weak pedal pulses, prominent pes cavus and hammertoes, and thin extremities with distal tapering in the legs. Cranial nerves were unremarkable. He had moderate weakness in all limbs especially distally, which was accentuated in the legs with bilateral foot drop. Reflexes were diffusely absent except for a trace response at the biceps. Vibration and pinprick perception was im-