We wanted to predict the prognosis of patients with CMT by the A/N ratio of the thickness and the circumference of the SCM muscle on ultrasonography, and we wanted to correlate the echogenecity of the affected muscle and the prognosis.

Ultrasonography was performed on 24 patients from June 2004 to March 2007. We measured the thickness and the cross sectional circumference of the SCM muscle at three levels; below the mastoid process, at the level of the carotid artery bifurcation and at the level of the sternum and clavicle. The ratio of the affected side to the normal side (the A/N ratio) of the SCM muscle was calculated. We performed followed up ultrasonography at 2 months intervals until the end of treatment. The Wilcoxon signed-rank test was used to correlate the A/N ratio before and after the treatment. Spearman's rank test was used to correlate the A/N ratio and the total treatment duration. Paired T-tests were used to correlate the echogenecity of the SCM muscle and the treatment duration divided by less than or greater than 12 months.

With measuring the thickness of the SCM muscle, the A/N ratio after treatment (1.36) was decreased compared with the initial A/N ratio (2.31) (p <0.05). The correlation between the A/N ratio of the thickness with the total treatment duration was statistically significant (p <0.05). The echogenecity of the affected SCM muscle was not correlated with the duration of treatment.

The A/N ratio of the thickness of the SCM muscle is useful to predict the prognosis of patients with CMT.