[Misdiagnosis of mitochondrial myopathies: a study of 12 thymectomized patients].
BACKGROUND
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.
Unité Clinique de Pathologie Neuromusculaire, Institut de Myologie, Groupe Hospitalier Pitié-Salpêtrière, AP-HP, Paris. r.benyaou@myologie.chups.jussieu.fr
R
R
Ben Yaou
P
P
Laforêt
H M
HM
Bécane
C
C
Jardel
D
D
Sternberg
A
A
Lombès
B
B
Eymard
D000284:Administration, Oral; D000293:Adolescent; D000328:Adult; D000368:Aged; D001763:Blepharoptosis / Q000209:etiology; D009202:Cardiomyopathies / Q000209:etiology; D002648:Child; D002675:Child, Preschool; D002800:Cholinesterase Inhibitors / Q000008:administration & dosage; D004272:DNA, Mitochondrial / Q000235:genetics; D003951:Diagnostic Errors; D018450:Disease Progression; D004576:Electromyography; D003576:Electron Transport Complex IV / Q000032:analysis; D005260:Female; D006319:Hearing Loss, Sensorineural / Q000209:etiology; D006801:Humans; D007267:Injections; D008297:Male; D008875:Middle Aged; D017240:Mitochondrial Myopathies / Q000150:complications / Q000175:diagnosis* / Q000235:genetics / Q000473:pathology; D018763:Muscle Fatigue; D018485:Muscle Fibers, Skeletal / Q000201:enzymology / Q000648:ultrastructure; D009157:Myasthenia Gravis / Q000175:diagnosis*; D009460:Neurologic Examination; D015835:Ocular Motility Disorders / Q000209:etiology; D012189:Retrospective Studies; D013934:Thymectomy; D019564:Unnecessary Procedures
D002800:Cholinesterase Inhibitors; D004272:DNA, Mitochondrial; D003576:Electron Transport Complex IV