Tripod pinch strength and thumb opposition are the major determinants of manual dexterity in Charcot-Marie-Tooth disease type 1A.

BACKGROUND Clinical features of Charcot-Marie-Tooth disease type 1A (CMT1A) include slowly progressive distal muscle weakness, atrophy and sensory loss. Upper-limb involvement results in reduced manual dexterity interfering with the execution of daily activities. OBJECTIVE To identify which hand function impairments are determinants of manual dexterity in CMT1A. METHODS In a cross-sectional, observational study, hand function (strength, mobility and sensory function) and manual dexterity (Sollerman hand function test) were evaluated in adults with CMT1A. Multiple linear regression analysis was used to determine the independent contribution of hand function variables on manual dexterity. Multifocal motor neuropathy (MMN) patients were chosen as a reference group with only motor impairments. RESULTS Forty-nine proven CMT1A patients (21 males, mean age 47+/-12) and 15 MMN patients (12 males, mean age 54+/-8) were studied. Hand strength, mobility and sensory functions were impaired in CMT1A compared with normal values. Limited manual dexterity was found in 94% of the CMT1A patients. From the investigated determinants (age, gender, grip and pinch strength, joint mobility, thumb opposition, touch, discrimination and vibration sense), tripod pinch strength, thumb opposition and, to a lesser degree, vibration sense were independently associated with manual dexterity (69% explained variance). Tripod pinch strength was also most strongly associated with manual dexterity in MMN. CONCLUSIONS Tripod pinch strength and thumb opposition are major determinants of manual dexterity in CMT1A and should therefore be the focus of intervention strategies that aim to preserve or enhance manual dexterity in CMT1A.