Of the 53 patients, nine were excluded because MRC score was not adequately documented and a further one was discounted due to having an additional diagnosis of CIDP. This left 43 patients, 22 males and 21 females, with 29 different mutations in the GJB1 gene (). Males were statistically younger, with a mean age of 37.2 years compared to 45.4 years for females (p < 0.01). Males had a mean CMTNS of 15.2 (n = 10, SD +/−4) and females a CMTNS of 12.6 (n = 13, SD +/−4.4). Seventy-three percent of patients were examined by a single author (MMR).
List of mutations in 43 patients studied with CMT1X.
In CMT1X patients, FDIO strength was higher in the non-dominant hand for 15/43 (34.9%) individuals and APB strength was higher in the non-dominant hand for 14/43 (32.6%) individuals. There were 22/43 (51.2%) patients with a weaker dominant hand based on a combined MRC score of FDIO and APB. No patient was found to have a stronger dominant hand for either FDIO or APB MRC strength scores individually or for the combined score.
When we categorised individuals into MRC strength scores of >4− and
4−, there was a significant difference in strength according to hand-dominance. We identified nine (20.9%) individuals who had a non-dominant FDIO score >4− and a dominant FDIO score
= 0.003) and eight (18.6%) patients who had a non-dominant APB score >4− and a dominant APB score
= 0.005). Using other MRC grades as a cut off did not show statistical significance in our sample population.
The mean strength scores for FDIO and APB were significantly higher in non-dominant compared to dominant hands (p < 0.0001; ). After adjustment for age and gender there was a mean 0.22 (95% CI: 0.12, 0.32) higher FDIO score for non-dominant hands compared to dominant hands and in a separate model there was a 0.30 (95% CI: 0.14, 0.47) higher APB score for non-dominant hands compared to dominant hands. In addition, males had a −1.14 (95% CI: −1.77, −0.52) lower APB score than females.
Comparison of hand muscles’ strength and ulnar and median nerve conduction studies between dominant and non-dominant hands.
Median nerve CMAPs were smaller in dominant hands compared to non-dominant hands, though this difference did not achieve statistical significance, most likely due to the small sample size (n = 18; p = 0.02; ). There was no significant difference in ulnar nerve CMAPs between dominant and non-dominant hands (n = 14; p = 0.89; ). There was no difference between dominant and non-dominant hands for median and ulnar nerve conduction velocities (data not shown).
When comparing FDIO to APB strength in the dominant hand of CMT1X patients, we found that APB was significantly weaker (p = 0.001; ). After adjustment for age and gender, there was a mean −0.40 difference in score for APB compared to FDIO (95% CI: −0.64, −0.15; p = 0.001). Furthermore, the associated nerve conduction studies demonstrated that median nerve CMAPs (APB) were significantly lower than the ulnar nerve CMAPs (ADM) in CMT1X patients (p < 0.0001; ). Similarly, conduction velocities were significantly slower in median nerves compared to ulnar nerves (p = 0.0005; ).
Comparison of MRC strength scores for FDIO and APB muscles in the dominant hand.
Comparison of nerve conduction studies between median and ulnar nerves.