Neuropsychological status of mitochondrial encephalomyopathies.

We studied 15 patients suffering from mitochondrial encephalomyopathies (MEM) by a neuropsychological screening procedure. Eight of the patients were diagnosed as having progressive external ophthalmoplegia (PEO), four mitochondrial myopathy, encephalopathy, lactic acidosis and stroke-like episodes (MELAS), and three Kearns-Sayre syndrome (KSS). Based on test results covering memory, orientation, non-verbal intelligence, drawing, arithmetics, word list generation, trail making and digit span, only four patients were regarded as normal, two in the PEO and two in the KSS groups, while five patients were found to be demented (two patients in the PEO and three patients in the MELAS groups). Although memory problems were very common, it is concluded that no uniform pattern of neuropsychological deficits is seen in MEM, that MELAS patients apparently are severely handicapped cognitively, and that considerable mental deterioration may be seen even with normal computer-assisted tomography findings.