INTRODUCTION Chronic progressive external ophthalmoplegia (CPEO) is a mitochondrial myopathy characterized by slowly progressive paralysis of the extraocular muscles. Although it can be seen in the absence of other clinical manifestations, CPEO is often associated with skeletal muscle weakness. It is a disorder of mitochondrial DNA where deletions of various lengths result in mitochondrial dysfunction. Since mtDNA codes for major components of cellular respiration tissues with a high oxidative demand, such as muscle, brain, and heart, are particularly affected. The extraocular muscles contain a higher than average amount of mitochondria so that these muscles are preferentially weakened. CPEO can occur as a sporadic mutation, as a point mutation of maternal mitochondrial tRNA, or as an autosomal dominant or autosomal recessive deletion of mtDNA. Kearns-Sayre syndrome (KSS) is a related mitochondrial myopathy characterized by early onset CPEO, pigmentary retinopathy, and cardiac conduction defects.
CLINICAL PRESENTATION CPEO begins in young adulthood with bilateral and symmetrical ptosis as the first clinical sign. Ophthalmoplegia follows months to years later and with progression the patient adopts a chin-up head posture with contraction of the frontalis muscles to help elevate the upper lids. Ultimately the globes are frozen in the midline. Exposure keratopathy and loss of superior visual field are major complications. Because the muscle weakness is symmetric, patients do not complain of diplopia. Rarely, ophthalmoplegia can be seen in the absence of ptosis. Weakness of facial, neck, and shoulder muscles may also be seen giving the patient a flat facial appearance. Occasionally neurological abnormalities may be associated including cerebral ataxia or pendular nystagmus. In KSS the retina shows a salt and pepper pattern of pigment degeneration. The ophthalmoplegia generally precedes the cardiac defects.
TREATMENT In most cases the major problem is loss of visual field due to poor function ptosis. This is treated with taping the lids up initially. In more advanced cases surgery will be needed. Since levator muscle function is poor, repair is usually by a very conservative frontalis suspension using a silicone rod. Care must be used since the Bells' phenomenon is extinguished. We prefer to simultaneously recess the lower lid upward to maintain a small palpebral fissure centralized over the pupil. Strabismus surgery can be useful in selected patients who experience diplopia. In all cases of CPEO a cardiac evaluation is essential to rule out KSS and conduction defects. Muscle biopsy shows ragged red fibers with abnormal aggregates of subsarcolemmal mitochondria. If present it may be managed with a pacemaker.
Chronic Progressive External Ophthalmoplegia (Contd.)
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