M. Koutroumanidis et al., REDUCED BRAIN-STEM EXCITABILITY IN MITOCHONDRIAL MYOPATHY - EVIDENCE FOR EARLY DETECTION WITH BLINK REFLEX HABITUATION STUDIES, Muscle & nerve, 19(12), 1996, pp. 1586-1595
Blink reflex (BR) was studied in 17 patients with histochemically and
genetically confirmed mitochondrial myopathy (MM). Fourteen patients h
ad chronic progressive external ophthalmoplegia (CPEO) associated with
a mild to moderate craniosomatic myopathy without any symptoms or sig
ns of central nervous system (CNS) involvement, 2 myoclonic epilepsy w
ith ragged red fibers syndrome, and 1 Kearns-Sayre syndrome, The mean
latencies of the early (R1) and late (R2) responses were prolonged (P
< 0.01 and P < 0.001, respectively), and the corresponding amplitudes
decreased (P < 0.001). Increased habituation of the reflex was clearly
observed in 10 out of 14 patients tested (71.4%), 9 of whom presented
CPEO. These findings suggest that the brain stem reticular network is
in a state of basal inhibition which is presumably due to a subclinic
al impairment of the cerebral cellular metabolism. Multimodal evoked p
otentials revealed abnormalities suggestive of CNS involvement in 7 ou
t of 17 patients (41.2%), 4 of whom had CPEO. These observations docum
ent the validity of BR in detecting clinically silent brain stem impai
rment in patients with apparently pure MM and provide important clues
for a further understanding of the underlying pathophysiology. (C) 199
6 John Wiley & Sons, Inc.