Hypersensitivity myocarditis induced by beta-blockers: an unexpected cause of abrupt deterioration in hypertrophic cardiomyopathy

Sir: A 32-year-old woman with a recent diagnosis of obstructive hypertrophic cardiomyopathy (maximal wall thickness = 22 mm; left ventricular ejection fraction = 75%), symptomatic for dyspnoea on moderate effort (New York Heart Association, NYHA, class II) received a single-drug treatment with metoprolol 50 mg bid, increased to 100mg bid after 1 week. The patient was not taking any other drug and had not received any other medicine in the past. Metoprolol was well tolerated and the dyspnoea improved (NYHA class I). The patient’s clinical history was otherwise uneventful with, in particular, no evidence of previous or coexisting allergic and/or autoimmune diseases. Routine blood tests were within normal limits, including the eosinophil count (80/mm3). After 4 weeks of treatment, the patient experienced palpitations and a worsening dyspnoea (NYHA class III). Electrocardiography registered frequent episodes of non-sustained ventricular tachycardia, while the left ventricular ejection fraction reduced to 32%. Her blood eosinophil count rose to 1050/mm3 and appeared partially degranulated, and there was an associated abnormal rise of plasma