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Chronic Progressive External Ophthalmoplegia

abbreviated CPEO

Overview

CPEO is a mitochondrial myopathy that predominantly affects the extraocular muscles and the levator palpebrae, producing slowly progressive, generally symmetric ophthalmoparesis and ptosis. Because progression is gradual and symmetric, patients frequently do not report diplopia (<30%) and may be unaware of their motility deficit, often adopting a compensatory chin-up head posture.

Onset and Course

  • Typical onset in adulthood (commonly 18–40 years), with ptosis often the first sign.
  • Slowly progressive over years; forced ductions are free (myopathic, not restrictive) and pupils are spared.
  • “CPEO-plus”: pigmentary retinopathy, cerebellar ataxia, peripheral neuropathy, sensorineural hearing loss, cardiac conduction block, and diabetes.
  • Kearns-Sayre syndrome defined as early-onset ophthalmoplegia and ptosis, pigmentary retinopathy, and cardiac conduction disease.

Genetics

  • Most commonly caused by a single large-scale mtDNA deletion (sporadic), but also by mtDNA point mutations and nuclear mtDNA-maintenance genes (e.g., POLG, RRM2B, TWNK).
  • Heteroplasmy matters: mutant load is far higher in skeletal muscle than in blood, so negative peripheral blood testing does not exclude CPEO.

Diagnostic Evaluation

  • Clinical eye and systemic exam — motility, lids, pupils, dilated fundus, cardiac review 1).
  • Screening labs — resting/post-exercise lactate and pyruvate, lactate:pyruvate ratio, creatine kinase, glucose/HbA1c; plus ECG given conduction-block risk 2).
  • Exclude mimics — myasthenia gravis (AChR/MuSK antibodies), oculopharyngeal and myotonic dystrophy 3).
  • Muscle biopsy (most accurate single test) — ragged-red fibers (Gomori trichrome) and COX-negative / SDH-hyperintense fibers; also enables respiratory-chain enzyme assays 4).
  • Genetic testing — whole mtDNA sequencing plus long-range PCR for deletions; muscle is the optimal tissue; nuclear gene panels when multiple deletions/depletion or a familial pattern is present 5)6).

Key Points

  • No blood test is confirmatory; diagnosis is clinical + histochemical + genetic.
  • A negative blood mtDNA test does not rule out the disease — proceed to muscle if suspicion is high 7).
  • Screen for and monitor cardiac conduction disease, a source of preventable morbidity/mortality 8).

Compare CPEO with Congenital Fibrosis of EOM (CFEOM)

Feature CPEO CFEOM
Nature of disorder Mitochondrial myopathy of extraocular muscle Congenital cranial dysinnervation disorder (neurogenic; abnormal CN III/IV/VI development with secondary muscle fibrosis)
Onset Adult, typically 18–40 yrs; ptosis first sign Congenital / present at birth
Course Slowly progressive over years Non-progressive (rare exceptions)
Symmetry / gaze Generally symmetric, diffuse limitation of all directions; superior rectus often prominently involved Fixed characteristic pattern — CFEOM1: eyes fixed in infraduction, absent upgaze; CFEOM2: large-angle exotropia
Ptosis Common, may be uni- or bilateral, progressive Congenital, typically bilateral; chin-up head posture
Diplopia Usually absent (<30%) due to gradual symmetric onsetAbsent; binocular vision typically never develops
Pupils Spared Spared in CFEOM1; poorly reactive in CFEOM2
Inheritance / genetics Single large-scale mtDNA deletion (~50%, sporadic); also nuclear mtDNA-maintenance genes (POLG, RRM2B, TWNK) and mtDNA point mutations Mendelian: CFEOM1 (AD, KIF21A); CFEOM2 (AR, PHOX2A); CFEOM3 (AD, TUBB3/TUBB2B/TUBA1A/KIF21A)
Systemic/associated features “CPEO-plus”: retinopathy, ataxia, neuropathy, deafness, cardiac conduction block, diabetes (Kearns-Sayre) Usually isolated; CFEOM3 may have developmental/CNS anomalies (e.g., Tukel syndrome)
Muscle biopsy Ragged-red / COX-negative fibers; mitochondrial abnormalities Not a mitochondrial biopsy diagnosis; muscle shows fibrosis/denervation changes
Orbital MRI Mild EOM atrophy with fatty/spongiform T1 signal EOM hypoplasia + hypoplastic ocular motor nerves

References

  1. McClelland C, Manousakis G, Lee MS. Progressive External Ophthalmoplegia. Curr Neurol Neurosci Rep. 2016.
  2. McFarland R, Taylor RW, Turnbull DM. The Neurology of Mitochondrial DNA Disease. Lancet Neurol. 2002.
  3. Li BY, Greenberg JH, Steigerwald C, et al. Pearls and Oy-Sters: Chronic Progressive External Ophthalmoplegia With Electrical Myotonia and Negative Initial Genetic Testing. Neurology. 2025.
  4. Gorman GS, Chinnery PF, DiMauro S, et al. Mitochondrial diseases. Nat Rev Dis Primers. 2016.
  5. Rodriguez-Lopez C, Garcia-Cardaba LM, Blazquez A, et al. Clinical, Pathological and Genetic Spectrum in 89 Cases of Mitochondrial Progressive External Ophthalmoplegia. J Med Genet. 2020.
  6. Ng YS, Bindoff LA, Gorman GS, et al. Mitochondrial Disease in Adults: Recent Advances and Future Promise. Lancet Neurol. 2021.
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