F-wave analysis in patients with carpal tunnel syndrome

The carpal tunnel syndrome (CTS) provides a model for analyzing the effects of focal nerve injury on F-waves. Twenty-four patients with clinical and electrodiagnostic features for unilateral (5) or bilateral CTS (19) were studied. F-waves were evaluated following 20 supramaximal stimuli and recording from abductor pollicis brevis muscles. Minimal and mean latencies, persistences, chronodispersion (CD), mean F/M amplitude ratios, and repeater waves were evaluated. CD's in those limbs with the most prolonged distal motor latencies (DML) were significantly greater than in those with less prolonged DML's; 80% or greater repeater waves were found almost exclusively in those hands with decreased M-wave amplitudes; and, mean F/M values were almost always larger in the hand with the more prolonged DML. The data support differing effects of demyelinating and axonal injury on F-waves and suggest physiological compensation in those hands with the more pronounced neurpathic dysfunction.