Introduction: The existence of neuropathy has been described in mitochondrial disorders such as MELAS, MERRF, Leigh's syndrome, the Kearns-Saye syndrome, myoneurogastro-intestinal encephalopathy and progressive external ophthalmoplegia and constitutes a basic component of the NARP (neuropathy, ataxia and retinosis pigmentosa). However, the general prevalence of the neuropathy and its characteristics within the mitochondrial encephalopathies is not well understood.
Objectives: To characterize the neuropathy and try to establish a genotype-phenotype correlation.
Patients and methods: Within study guidelines, we made a retrospective study of 27 patients, diagnosed as having mitochondrial disease, who had had neurophysiological studies (EMG-ENG). In those in whom neuropathy had been found we analysed the clinical, neurophysiological and genetic characteristics.
Results: Neuropathy was present in 37% of the patients who had an average age of 13 years, ranging from 1 to 25 years. Syndromic diagnoses were: 7 encephalomyopathies, one MELAS, one MERRF and one NARP. Four of the patients were classified genetically. In all but two of the patients the neuropathy was asymptomatic. The biochemical alterations seen were: deficit of Complex 1 in 3 patients, of complex III in 3 patients, of complex IV in 2 and of pyruvate dehydrogenase in one patient. The type of neuropathy found was varied, with predominance of axonal-type motor neuropathy but no correlation with either biochemical defects or genetic diagnosis.
Conclusions: Neuropathy is a common finding in mitochondrial disorders and probably is under-diagnosed. The axonal form predominates. We have not been able to establish correlations between phenotypes and genotypes.