Benign calf amyotrophy: clinicopathologic study of 8 patients.

BACKGROUND: The benign focal amyotrophy disorders have been described since 1959 for the upper limbs and since 1981 for the lower limbs. The clinicopathologic features have pointed to a restricted and self-limiting form of motor neuron disease.

OBJECTIVE: To describe the clinical, electromyographic, and muscle histopathologic features in 8 patients with benign calf amyotrophy.

DESIGN: Retrospective review of patient charts, electromyograms, and muscle histopathology.

PATIENTS AND RESULTS: Eight patients, aged 37 to 88 years, developed insidiously progressive calf muscle weakness and wasting during 1 to 5 years. The gastrocnemius weakness and wasting were bilateral in 4 patients. Initial progression of symptoms was followed by disease stabilization. None had a history of poliomyelitis or family history of neuromuscular disease. Creatine kinase values were mildly elevated in 5 patients. The electromyographic and muscle histopathologic findings were consistent with a chronic neuropathic disorder. Despite the restricted calf muscle involvement clinically, the electromyographic abnormalities suggested more diffuse lower limb involvement. Further studies, including DNA tests and muscle-based protein studies, excluded several types of inherited neuromuscular disorders.

CONCLUSIONS: Benign calf amyotrophy is a variant of the benign focal amyotrophy disorders. The etiology for these disorders is unknown. Studies to exclude other causes of calf amyotrophy and careful follow-up examinations to document disease stabilization are necessary to diagnose this uncommon disorder.