Mitochondrial disorder mimicking ocular myasthenia.

OBJECTIVES

Ocular myasthenia (OM) and mitochondrial disorder (MID) may be easily mixed up, if the MID presents with similar manifestations as OM and if MID manifestations progress only slowly.

CASE REPORT: In a 69yo Caucasian female OM was diagnosed at age 54y. Six years after onset the diagnosis was challenged, because the response to cholinergic medication was weak, acetyl-cholin-receptor antibodies were only marginally elevated, creatine-kinase was slightly elevated, and because the patient's mother had developed dementia. Resting lactate was normal but the lactate-stress-test was highly abnormal. Muscle biopsy was indicative of a MID and biochemical investigations revealed a complex I defect.

CONCLUSIONS

MID may be easily mixed up with OM, particularly at onset of a MID with only mild manifestations. The diagnosis of OM should be challenged if untypical clinical features develop or clinical manifestations do not respond to cholinergic medication.