[A case of malignant thymoma associated with Eaton-Lambert-type neuromuscular transmission block and sensorimotor neuropathy].

The patient is a 73-year-old male. In January 1988, he noticed sensory disturbance and muscular weakness of his extremities. His thymoma was found in July 1988, and in October 1988, he was admitted to our hospital for treatment. Neurological examination showed muscular weakness, muscular atrophy, fasciculation, and distal dominant sensory disturbance of his right upper extremity and his bilateral lower extremities. The immunological examination showed an increase in serum IgG, gamma-globulin, OKT3 and OKT4 lymphocytes. Electromyographic studies showed severe waxing by repeated stimulations (200% by 10 Hz; 330% by 20 Hz), very low M wave amplitude by single stimulation, and post-tetanic exhaustion. An Eaton-Lambert-type neuromuscular transmission block was thus thought to exist. Concentric needle electromyography showed a neurogenic pattern. The sensory and motor nerve conduction velocity was delayed. Microscopic examination of biopsied skeletal muscle showed neurogenic change. A sural nerve biopsy specimen showed a decrease in the number of myelinated fibers (fiber density 4333/mm2), segmental demyelination, remyelination, and mild axonal change. Thymectomy was performed and pathological examination showed invasive thymoma of predominantly the epithelial type. His muscular weakness and sensory disturbance improved gradually after thymectomy. On the postoperative immunological examination, serum IgG, gamma-globulin, OKT3 and OKT4 lymphocytes were normalized. On the other hand, OKT8 lymphocytes were increased and the OKT4 to OKT8 ratio was decreased. The electromyographic studies showed no waxing, normal M wave amplitude, and no post-tetanic exhaustion. Therefore, we consider that an Eaton-Lambert-type neuromuscular transmission block and sensorimotor neuropathy in this case were caused by the immunological abnormality accompanying malignant thymoma.