[Misdiagnosis of mitochondrial myopathies: a study of 12 thymectomized patients]

Rev Neurol (Paris). 2006 Mar;162(3):339-46. doi: 10.1016/s0035-3787(06)75020-2.
[Article in French]


Introduction: Myasthenia gravis and mitochondrial myopathies have common symptoms (fatigability, ophthalmoplegia) that could lead to diagnosis confusion.

Methods: We systematically reviewed medical history and ancillary investigations regarding 12 patients (7F/5M, mean age 47+/-14 years) having a mitochondrial myopathy but who were previously misdiagnosed as autoimmune myasthenia gravis and in whom a thymectomy was performed.

Results: Ocular palsy, ptosis and bulbar palsy were present in all patients. Limb fatigability was present in 9 cases. Symptoms were fluctuant but without remission. The misdiagnosis of myasthenia was based on the following arguments: 1) decremental EMG response (2 cases); 2) positive injectable anticholinesterase drugs test (3 cases); 3) partial response to oral anticholinesterase medications (2 cases); 4) AChR antibodies titer of 0.6 nM considered as positive (1 case). A multisystemic involvement was present in 5 patients: peripheral neuropathy (2 cases), deafness (2 cases), cardiopathy (3 cases), cerebellar involvement (2 cases) and myoclonia (1 case). The diagnosis of mitochondrial myopathy (at a mean age of 38+/-12 years) has been certified on the results of muscle biopsy showing mitochondrial proliferation (12 cases) and deleted mitochondrial DNA (8 cases).

Conclusions: In a patient presenting with oculomotor symptoms and muscle fatigability, progressive course and multisystemic involvement are major arguments for a mitochondrial myopathy. In the absence of relevant criteria arguing for Myasthenia Gravis (significant variability of muscle weakness, positive titer of anti-AChR or anti-MuSK antibodies, decremental EMG response), a muscle biopsy is required before indication of thymectomy to exclude a mitochondrial disease.

Publication types

  • Case Reports
  • English Abstract
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Administration, Oral
  • Adolescent
  • Adult
  • Aged
  • Blepharoptosis / etiology
  • Cardiomyopathies / etiology
  • Child
  • Child, Preschool
  • Cholinesterase Inhibitors / administration & dosage
  • DNA, Mitochondrial / genetics
  • Diagnostic Errors*
  • Disease Progression
  • Electromyography
  • Electron Transport Complex IV / analysis
  • Female
  • Hearing Loss, Sensorineural / etiology
  • Humans
  • Injections
  • Male
  • Middle Aged
  • Mitochondrial Myopathies / complications
  • Mitochondrial Myopathies / diagnosis*
  • Mitochondrial Myopathies / genetics
  • Mitochondrial Myopathies / pathology
  • Muscle Fatigue
  • Muscle Fibers, Skeletal / enzymology
  • Muscle Fibers, Skeletal / ultrastructure
  • Myasthenia Gravis / diagnosis*
  • Neurologic Examination
  • Ocular Motility Disorders / etiology
  • Retrospective Studies
  • Thymectomy*
  • Unnecessary Procedures*


  • Cholinesterase Inhibitors
  • DNA, Mitochondrial
  • Electron Transport Complex IV