Peripheral neuropathy in patients with the 3243A>G mutation in mitochondrial DNA

Peripheral neuropathy is one of the clinical manifestations of the MELAS (mitochondrial encephalopathy with lactic acidosis and stroke-like episodes) syndrome, but its frequency and phenotypic variability have not been properly characterised. We therefore studied the clinical and electrophysiological features of peripheral neuropathy in 32 patients with the 3243A > G mutation in mitochondrial DNA by using clinical examination, assessment of Neuropathy Symptom Score, Neuropathy Disability Score, and electrophysiological examinations. Seven patients (22 %; 95 % confidence interval, 9-40 %) fulfilled the electrodiagnostic criteria for polyneuropathy. Mixed axon loss and demyelinating sensorimotor neuropathy was the most common type of polyneuropathy, while one patient presented with uniform demyelinating sensorimotor polyneuropathy. Sensory more than motor neuropathy was diagnosed in four patients. Clinically and electrophysiologically confirmed carpal tunnel syndrome (CTS) occurred in three patients (9.4 %), suggesting a higher prevalence than in the general population. Patients with neuropathy were in general more severely affected than those without neuropathy, although no correlation was found between the presence of neuropathy and the degree of mutant heteroplasmy in muscle. Higher age and male gender were associated with an increased risk of neuropathy. Our results show that peripheral neuropathy is not uncommon in patients with the 3243A > G mutation, and they also may have an increased risk of CTS.