Spinal myoclonus with vacuolar degeneration of anterior horn cells.

Myoclonic contractions of muscles in the abdominal wall and lower extremities developed in a 47-year-old paraplegic woman. The spinal cord was compressed from T-3 to T-8 by an extradural renal cell carcinoma metastasis. To our knowledge, previous studies of patients with sinal myoclonus have not reported a pathologic correlation. In our patient, a focal morphologic change that consisted of vacuolar degeneration and chromatolysis of anterior horn cells was found at the levels of the spinal cord corresponding to the involved muscles. The myoclonus may be spinal in origin and due to an increased excitability of anterior horn cells during the period of sublethal injury.