Lower Leg MRI Features in Axonal Charcot-Marie-Tooth Patients with MFN2 Mutations

ABSTRACT

BACKGROUND: Mutations in mitofusin2 (MFN2) are a major underlying cause of axonal Charcot-Marie-Tooth neuropathy (CMT). It has been reported that patients with an early age of onset ( or =10 years, LO) in CMT2A with MFN2 mutations. There are few studies about CMT patients with MRI studies and we performed leg MRIs for better understanding of CMT2A. METHODS: We identified 19 patients (EO=10; LO=9) with MFN2 mutations. We used functional disability scales and CMT neuropathy scales for the grading of disability. Nerve conduction studies and MRIs of the lower leg were performed in all patients. RESULTS: We confirmed that EO had more severe leg muscle involvement than LO by leg MRI. In 7 out of 9 in LO, there were some degree of asymmetric leg muscle weakness and MRI findings explained the nature of asymmetry, that is, asymmetric cross-sectional areas or fatty infiltration. MRI of EO showed marked fatty infiltration on all three compartments whereas that of LO showed rather selective involvement of the posterior compartment. These results were well correlated with clinical findings that in LO, five patients could not do toe walking whereas only one could not do heel walking. CONCLUSIONS: MRI of the leg may be a useful tool for evaluating axonal CMT neuropathy, and asymmetric leg muscle weakness may be the characteristics of an axonal CMT. In addition, more prominent involvement of the posterior leg in LO is a very interesting phenomenon, which is in contrast to the length-dependent involvement in congenital demyelinating neuropathy.