Lower limb manual muscle testing in the early stages of Charcot-Marie-Tooth disease type 1A

Charcot-Marie-Tooth disease (CMT) is a genetically and clinically heterogeneous disorder that affects approximately one in 2,500 individuals. CMT 1A, which is due to a duplication in the area containing the PMP-22 gene on chromosome 17, is the most frequent CMT subtype. To date, there is no consensus among authors about which muscles are weakened in the early stages of CMT, even though this knowledge would be crucial for deciding the most appropriate interventions to restore balance between muscles and prevent the development of deformities. The aim of this study was to evaluate the strength of several lower limb muscles in the early stages of CMT 1A. In a series of 45 patients (age 10-72 years; 21 males, 24 females) affected by CMT 1A, we evaluated 83 non-operated lower limbs that corresponded to the two milder stages of a five-level functional classification. The strength of two foot muscles, seven leg muscles, two thigh muscles, and three pelvic girdle muscles was graded using the manual muscle testing techniques of Daniels and Worthingham; the power of the triceps surae was graded, in the prone position, using a 4-level scale of ability to raise the heel from the floor. Muscle strength was determined on the basis of interobserver agreement estimated by kappa statistics between two observers. The flexor hallucis brevis and lumbricals were very weak in all the limbs; the leg muscles were strong in more than 90% of limbs, except the peronei (strong in 83.13%); all the triceps surae were strong in the prone test, but 16.87% were weak in the standing test; all the proximal muscles were strong. In the large majority of patients in the early stages of CMT 1A, the intrinsic foot muscles are very weak and the leg and proximal muscles are strong.