Abstract Body (Do not enter title and authors here): Human metapneumovirus (hMPV) is a well-known paramyxovirus that has primarily been associated with respiratory illness. Extrapulmonary complications, such as pericarditis and pericardial effusion, are exceptionally uncommon. We report a case of hMPV-associated pericarditis in an immunocompetent patient with a solitary kidney, where standard anti-inflammatory therapy was contraindicated.

A 77-year-old man with a history of renal oncocytoma status post unilateral nephrectomy presented with six days of exertional dyspnea followed by midsternal chest pain with radiation to the left shoulder. Labs revealed mild leukocytosis, baseline renal dysfunction, elevated NT-proBNP and elevated inflammatory markers. High-sensitivity troponin on three serial measurements remained stable. ECG with ST elevations in multiple leads initially raised suspicion of acute coronary syndrome. Given the pleuritic nature of the pain and a stable low-level troponin elevation, urgent catheterization was deferred. CT pulmonary angiogram was negative for PE but showed a pericardial effusion. Transthoracic echocardiogram confirmed small to moderate circumferential pericardial effusion without tamponade physiology. A respiratory viral PCR returned positive for hMPV infection. Though the patient developed acute atrial fibrillation with rapid ventricular response, he remained hemodynamically stable and did not meet criteria for pericardiocentesis. After nephrology and cardiology consultation, NSAIDs and colchicine were avoided due to renal risk. He was initiated on high-dose aspirin and experienced symptomatic improvement after only 4 doses. He was discharged in stable condition with a plan for two-week taper and outpatient follow-up.

While viral pericarditis is not uncommon, hMPV is rarely identified as the causative agent. A literature review reveals only a handful of reported cases of hMPV-induced pericarditis, with even fewer occurring in the context of impaired renal reserve. This case underscores the importance of including hMPV in the differential diagnosis of viral pericarditis. It also highlights a critical management challenge: while NSAIDs and colchicine remain first-line therapies for pericarditis, renal dysfunction may preclude their use and necessitate alternative treatment strategies. Our patient achieved clinical improvement with aspirin monotherapy alone, demonstrating its potential utility in patients with contraindications to standard therapy.