Muscle electrophysiology in patients with advanced breast cancer.

Sixty-one consecutive patients with advanced breast cancer (defined as metastatic disease) and 20 normal age- and sex-matched controls were admitted to a prospective study designed to assess muscle electrophysiology. Nutritional status, lean body mass, and ultrasonographic measurement of the triceps brachialis, sternomastoid, and adductor pollicis muscles were determined in patients and controls. In addition, tumor mass and performance status were determined in the patient group. Electrophysiology of the adductor pollicis muscle was assessed during isometric voluntary maximum effort and during electrical stimulation via the ulnar nerve (80-120 V, 50-100 msec). Nutritional status, lean body mass, and ultrasonographic measurements of the triceps brachialis, sternomastoid, and adductor pollicis were not significantly different between patients and controls. Maximum strength after supramaximal stimulation at 50 Hz was 34 +/- 15 N in patients, versus 40 +/- 9 (P less than .01) N in controls. Relaxation velocity was 336 +/- 149 N/sec in patients, versus 507 +/- 251 (P = .02) N/sec in controls. Fatigue (% of initial strength after 30 sec of stimulation) was 67% +/- 22% in patients, versus 79% +/- 17% (P = .03) in controls. Muscle electrophysiology did not correlate with tumor mass or performance status. It was concluded that patients with advanced breast cancer have abnormal muscle electrophysiology that is not due to abnormal nutritional status or decreased muscle mass. More research is needed to better characterize this disorder and to better define its cause.