Overwork weakness in Charcot-Marie-Tooth disease.

OBJECTIVE: To determine the incidence of overwork weakness in Charcot-Marie-Tooth disease (CMT).

DESIGN: Prospective survey.

SETTING: Rehabilitation department for CMT in an Italian tertiary care hospital.

PARTICIPANTS: A total of 106 outpatients with CMT, selected for absence of other causes of weakness (age range, 11-69y), and 48 healthy volunteers (controls).

INTERVENTIONS: The strength of 2 intrinsic hand muscles (abductor pollicis brevis [APB], first dorsal interosseous) in the dominant and nondominant hands was graded by using manual muscle testing and a modified Medical Research Council (MRC) Scale.

MAIN OUTCOME MEASURES: The side of the stronger muscle and the difference in strength between the nondominant and dominant muscles.

RESULTS: Muscles were stronger on the nondominant side in 65.57% of patients versus 1.04% of controls, and on the dominant side in .94% of patients versus 84.38% controls. The difference in strength for first dorsal interosseous was .51 in patients and -.32 in controls (P>.01). The difference in strength for APB was .65 in patients and -.35 in controls (P>.01).

CONCLUSIONS: CMT muscles in the dominant hand are weaker than in the nondominant hand. This may be the result of overwork weakness.