Influenza Myocarditis and Myositis: Case Presentation and Review of the Literature

Abstract Myocarditis, a general inflammatory condition of the heart muscle, can result from a variety of etiologies, the most common being viral. Despite common pathogens, concomitant myocarditis and myositis remains a rare event. Although a common cause of respiratory illness, extrapulmonary infections with influenza are infrequent. We describe the case of a patient who presented to our centre with concomitant "seasonal" H1N1 influenza A myocarditis further complicated by pan-myositis. The patient's condition rapidly declined, eventually requiring biventricular mechanical support, in addition to multilimb fasciotomies. The cardiac support required was progressive, from a percutaneous left ventricular assist device, to extracorporeal membrane oxygenation, to eventual biventricular assist device support for bridge-to-transplantation. This case motivated a detailed review of the literature (a total of 29 cases were identified), in which we found that patients with influenza myocarditis/myositis were predominantly female (63%) and young (mean age 33.2 years) and continue to have a high incidence of morbidity and mortality (27%). As a result of its atypical pattern, the 2009 H1N1 pandemic strain has gained attention. From our review, we found 7 patients with of 2009 H1N1 pandemic influenza myocarditis. Serial serum cytokine analysis did not demonstrate a "cytokine storm," which has been associated with other virulent influenza strains. The PB1-F2 marker in particular has been associated with a vigorous cytokine response. The 2009 H1N1 and "seasonal" influenza strains lack this marker. In those patients with community-acquired influenza, interleukin-6 has been shown to correlate with symptoms. For patients with myocarditis resulting in shock, mechanical circulatory support has gained acceptance as a means to recovery or transplantation.