8歳児における遷延性モビッツI型房室ブロックを呈したマイコプラズマ肺炎誘発性発疹・粘膜炎

Mycoplasma pneumoniae is a known causative agent for community-acquired pneumonia. Extrapulmonary manifestations can occur independently of pneumonia in Mpneumoniae infection, and cardiac involvement is around 1% to 5%. Myocarditis and pericarditis are often associated with mycoplasma infections.

An 8-year-old girl presented with fever, conjunctivitis, rash, and swelling of the lips and extremities. Laboratory findings showed thrombocytopenia, hyponatremia, elevated inflammatory markers, elevated pro-B-type natriuretic peptide, elevated troponin I, and negative respiratory viral panel. Electrocardiogram indicated normal sinus rhythm, and echocardiography showed a small pericardial effusion, otherwise unremarkable. Intravenous immunoglobulin was initiated for presumed atypical Kawasaki disease. The patient's hospital course was notable for the development of asymptomatic Mobitz type I (Wenckebach) second-degree atrioventricular block on telemetry. Mycoplasma serology was performed, which was positive for Mpneumoniae IgM, leading to the diagnosis of Mpneumoniae-induced rash and mucositis (MIRM) with cardiac involvement. Doxycycline was initiated, which was followed by gradual normalization of inflammatory markers, troponin I, and resolution of pericardial effusion. Mobitz type I atrioventricular block subsequently resolved.

Mpneumoniae is an atypical bacterium transmitted via respiratory droplets. Extrapulmonary manifestations are caused by direct invasion or by molecular mimicry-induced immune response.

MIRM mimics the symptoms of Kawasaki disease. Cardiac involvement in MIRM in the form of myopericarditis is common, whereas conduction abnormalities are rare in the pediatric age group. Early diagnosis of conduction abnormalities results in improved outcome.