Multifocal motor neuropathy with conduction block: slow but not benign.

OBJECTIVE: To describe a patient with multifocal motor neuropathy with conduction block who had annual clinical and physiological examinations for 18 years but declined treatment for personal reasons. DESIGN: Case report. SETTING: Collaboration between 2 academic tertiary care hospitals. Patient One patient with multifocal motor neuropathy with conduction block. RESULTS: At age 44 years, there was weakness and wasting of the left biceps with conduction block in the left musculocutaneous and right ulnar nerves. The left median nerve was inexcitable. The right median, ulnar, and left peroneal nerves developed axonal change (loss of distal compound muscle action potential amplitude) at years 5, 12, and 13. By 2005, new weakness had appeared in 20 muscles (16 in the arms); he could not use a keyboard, button buttons, or write his name. Nerves that initially showed conduction block became inexcitable over the course of the illness. CONCLUSIONS: Multifocal motor neuropathy with conduction block is a disease that may be "only" slowly progressive but is not always benign. Nerves showing conduction block may develop axonal change. Better markers for this disease are needed.