A syndrome of asymmetric limb weakness with motor conduction block.

We describe 3 patients with asymmetric limb weakness, fasciculations (2 patients), relatively preserved reflexes, normal cranial nerves, and few or no sensory abnormalities. The symptoms had been progressive over 1 to 15 years. Detailed motor nerve conduction studies showed conduction block and slowing localized to sharply circumscribed areas 30 to 100 mm long in several nerves in each patient. By contrast, the sensory conduction studies over the same nerve segments were normal, indicating very selective involvement of motor fibers. Sural nerve biopsies showed minor changes that varied among the patients. One patient had high levels of anti-GM1 antibodies, 1 had mildly elevated levels, and 1 had high levels of only asialo-GM1 antibodies. Treatment with immune suppressive therapy has produced minimal improvement in 1 patient.