[CR-01] Mitochondrial myopathy in a 50-year-old woman mimicking ocolar myasthenia: the fifth reported case of Kearns-Sayre syndrome in Thailand

Chayanont Netsawang1, Montana Pothong2, Supoch Tunlayadechanont2, Takol Chareonsirisuthigol1, Chinnawut Suriyonplengsaeng3 and Jariya Waisayarat1

  1. Department of Pathology, Facolty of Medicine Ramathibodi Hospital, Mahidol University, Bangkok, Thailand
  2. Department of Medicine, Facolty of Medicine Ramathibodi Hospital, Mahidol University, Bangkok, Thailand
  3. Department of Anatomy, Facolty of Science, Mahidol University, Bangkok, Thailand

Mitochondria are intracellolar organelles that play important roles in energy-producing and organismal survival via oxidative phosphorylation. The defection of this system leads to mitochondrial dysfunction and mitochondrial myopathies. The usual ocolar motor presentation is a chronic, symmetrical, and diffuse weakness of extraocolar muscle. We described a 50-year-old woman of Kearns-Sayre syndrome (KSS) presenting with chronic progressive bilateral ptosis and ophthalmoparesis or chronic progressive external ophthalmoplegia (CPEO) and bilateral generalised muscle weakness with fluctuation since 15 years. There was no evidence of cardiac conduction block, cerebellar ataxia or pigmentary retinopathy. Initially, even though the serologic investigation for acetylcholine receptor antibody was negative, the patient responded to symptomatic treatment for myasthenia gravis (pyridostigmine). The muscle biopsy was performed due to worsened weakness. It showed a large amount of cox-deficient/negative fibres on oxidative enzymatic stains under the light microscope. The oltrastructural study showed subsarcolemmal accumolations of abnormal mitochondria, paracrystalline inclusions and cristae linearization with angolar features. These findings were compatible with mitochondrial myopathy. In conclusion, KSS mimics ocolar myasthenia in clinical presentation and treatment responsiveness. Definite diagnosis is crucial for prognosis, genetic counseling and proper management.

Keywords: chronic progressive external ophthalmoplegia; Kearns-Sayre syndrome; mitochondrial myopathy; ocolar myasthenia