Eye movements of Charcot-Marie-Tooth diseases

Abstract

Charcot-Marie-Tooth (CMT) diseases is a clinically and genetically heterogeneous group of peripheral nerve disorders characterized by distal muscle weakness and atrophy. There have been some reports of CMT diseases with CNS involvement, especially cerebellar atrophy. Recently, families with CMT type muscular atrophy with cerebellar ataxia have been increasingly reported, and it has been proposed as a new disease entity. However, the pathogenesis of CMT diseases with CNS involvement is unknown. We reported eye moments recorded electro-oculographically in seven patients with Charcot-Marie-Tooth diseases. Brain MRI demonstrated slight cerebellar atrophy in only one case and no apparent abnormality in the other six cases. No abnormal eye movement was found in two patients with CMT type 1, but some abnormal eye movements were surprisingly observed in five patients including one with CMT type 1, three with CMT type 2, and one with HNPP. The observed eye movement abnormalities were lateral-gazed nystagmus in 2 patients, impaired smooth pursuit in 5 patients, saccadic hypometria in 3 patients, and a decrease of saccadic velocity in 2 patients. In all 5 patients, decreases in the slow phase of OKN and of visual suppression on the caloric test were observed. From eye movements, three cases were diagnosed as cerebellar involvement, one as cerebellar and brain stem involvements, and one as suspicious cerebellar deficit. One patient with CMT type 1 showing cerebellar and brain stem involvements and abnormal eye movement was genetically diagnosed as CMT 1A, which is the most common form of CMT disease. The findings suggest that CMT disease with cerebellar or brain stem involvement is more frequent than has been previously reported. Further investigation is necessary on eye movement abnormalities in patients with CMT disease. Examination of eye movement was a very useful and sensitive indicator in the screening of CMT patients to evaluate any central nervous deficit, especially concerning cerebellar and brainstem involvements.