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Excerpt from Chronic Progressive External OphthalmoplegiaSynonyms, Key Words, and Related Terms: CPEO, abiotrophic ophthalmoplegia, CPEO with ragged red fibers, oculocraniosomatic neuromuscular disease, ocular myopathy, Olson disease, Kearns-Sayre-Daroff syndrome, Kearns-Sayre syndrome, progressive external ophthalmoplegia plus, extraocular muscle paralysis Please click here to view the full topic text: Chronic Progressive External OphthalmoplegiaBackgroundChronic progressive external ophthalmoplegia (CPEO) is a disorder characterized by slowly progressive paralysis of the extraocular muscles. Patients usually experience bilateral, symmetrical, progressive ptosis, followed by ophthalmoparesis months to years later. Ciliary and iris muscles are not involved. CPEO is the most frequent manifestation of mitochondrial myopathies. CPEO in association with mutations in mitochondrial DNA (mtDNA) may occur in the absence of any other clinical sign, but usually it is associated with skeletal muscle weakness. Kearns-Sayre syndrome (KSS) is a related mitochondrial myopathy that demonstrates the following: CPEO, onset before age 20, and pigmentary retinopathy. KSS also has at least one of the following: cardiac conduction defects, cerebrospinal fluid (CSF), protein of greater than 100 mg/dL, and a cerebellar syndrome. Other abnormalities in KSS can include mental retardation, Babinski sign, hearing loss, seizures, short stature, delayed puberty, and various endocrine disorders. CPEO can also be a sign in the following disorders: oculopharyngeal dystrophy, myasthenia gravis, and Graves disease. PathophysiologyMitochondrial DNA encodes for essential components of the respiratory chain. Deletions of various lengths of mtDNA results in defective mitochondrial function, particularly in highly oxidative tissues (eg, muscle, brain, heart). Extraocular muscles are affected preferentially because their fraction of mitochondrial volume is several times greater than that of other skeletal muscle. Impaired protein synthesis in these mitochondria accounts for the histological hallmark of the mitochondrial myopathies. When muscle fibers are stained with Gomori trichrome stain, an abnormal accumulation of enlarged mitochondria is seen beneath the sarcolemma. These fibers are called ragged red fibers due to their unusual appearance and dark red color. A variable proportion of deleted mtDNA has been found to be present in different tissues from the same patient. The balance of oxidative demands of a given tissue and the proportion of deleted mtDNA it contains ultimately will determine whether the tissue is affected clinically. FrequencyUnited StatesCPEO is rare. SexIn KSS, boys and girls are affected equally. AgeIn KSS, onset of CPEO is before age 20. Please click here to view the full topic text: Chronic Progressive External Ophthalmoplegia |
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