[P3-146] Double trouble: mitochondrial myopathy or myasthenia gravis?
A 15-year-old girl presented with creatine kinase (CK) elevation (20.000 u/L, N<300) and recurrent muscle pain. She had been diagnosed with juvenile myasthenia at the age of 8 years when she presented with diplopia, weakness in limbs and fatigue. Serum acetylcholine receptor (AChR) antibody was negative and electromyography (EMG) showed decremental response. Symptomsmoderately improved with steroids and pyridostigmine.At age 14.5 years she was admitted for pain in the limbs and elevation in CK (10.366 u/L); myositis was considered and improved by hydration. EMG showed no pathology. Similar attack recurred after 5 months and treated with intravenous immunoglobulin; pain and tenderness subsided and serum CK levels declined to normal levels. Although moderate ptosis, ophthalmoplegia persisted. The third episode was observed one month later: on neurological examination she had total ophthalmoplegia,weakness and tenderness in arm and leg muscles. Serum dermatomyositis antibody panel was negative. Muscle biopsy showed ragged red fibers and COX deficient fibers; mitochondrial myopathy was diagnosed and mitochondrial cocktail was started. This case illustrates a certain group of mitochondrial myopathies where symptoms can suggest myasthenia and myositis. Interestingly patients, as the current one, may benefit from immunomodulatory treatment.