Consequences of misdiagnosing mitochondrial disorder.

Diagnosing mitochondrial disorder remains a challenge. In a 75-year-old women, with short stature, muscle cramps, ptosis, fasciculations and progressive, proximal limb weakness and wasting, hyponatriemia, abnormal lactate-stress-test, and slightly abnormal electromyography, muscle biopsy suggested granulomatous myositis. Corticosteroids and azathioprin were ineffective. After a second work-up amyotrophic-lateral-sclerosis was diagnosed. Riluzole was started, without effect. She developed respiratory insufficiency, requiring mechanical ventilation. Apical ballooning was found. After switching to non-invasive positive pressure ventilation and physiotherapy, she markedly improved. After a third diagnostic work-up, mitochondrial disorder was suspected. Unfortunately, she died suddenly from a cardiac arrhythmia at home. Mitochondrial disorder may mimic motor neuron disease, muscle biopsy may mimic myositis, and may show only little evidence for respiratory chain disorder.