Cardiac magnetic resonance aids in the diagnosis of mitochondrial cardiomyopathy

A 29-year-old woman presented with symptoms of cough, shortness of breath, and wheezing. She was diagnosed with bronchitis, but did not improve with empirical therapy, including antibiotics, inhalers, and prednisone. She subsequently developed chest pain that was worse when lying down, and a chest X-ray demonstrated cardiomegaly. This radiographic finding prompted further investigations. Her past medical history was notable for respiratory distress at birth and small stature growing up. She was diagnosed with a heart murmur at age 15, but investigations performed at that time were unrevealing. She also suffered from hearing loss. In retrospect it was discovered that several members in her maternal family, including her mother, grandmother, and aunt, also suffered from hearing loss. In addition, her mother had type 2 diabetes and a history of stroke and seizures. On physical examination, she was a short, thin young woman with a body mass index of 17, wearing bilateral hearing aids. Her vital signs were normal. Cardiac auscultation revealed a 2/6 systolic ejection murmur. Laboratories revealed an elevated serum creatinine level of 1.36 mg/dL and a markedly elevated B-type natriuretic peptide level of 1417 pg/mL. The electrocardiogram was abnormal with evidence of right atrial enlargement, inferior Q waves, poor R wave progression, and inferolateral T wave inversions. Transthoracic echocardiography revealed severe, concentric left ventricular (LV) hypertrophy with a septal wall thickness of 17 mm (Figure 1). LV systolic function was hyperdynamic (Movie I of the online-only Data Supplement), while diastolic filling demonstrated a restrictive pattern. The right ventricle also demonstrated increased wall thickness but was of normal chamber size and function. There was a moderate-sized pericardial effusion measuring 1.8 …