Rhabdomyolysis Due to Influenza A

Acute viral myositis is an uncommon condition that can be related to infections such as influenza A, influenza B, dengue, and enteroviruses. When complicated by rhabdomyolysis, it becomes an even rarer and potentially severe event, requiring immediate recognition to avoid critical complications. In this context, we present the case of W.S., a previously healthy young person reporting fever, intense myalgia, dry cough, runny nose, sore throat, nausea, and vomiting. He sought care at an emergency unit (UPA) on the fifth day of symptoms, soon after developing dark urine, and was referred for hospital admission with an initial suspicion of dengue (group C). On admission, he was lucid, oriented, hemodynamically stable, and afebrile, reporting worsening prostration and myalgia, but already noting improvement of rhinorrhea and sore throat. He denied bleeding, abdominal pain, recent exertion, trauma, use of medications or supplements, and drug use. Initial laboratory tests showed platelets 133,900/mm³, normal renal function, elevated AST (1325 U/L) and ALT (225 U/L), normal bilirubin, urine with hematuria and myoglobinuria, LDH 9,320 U/L, and CPK >1,000 U/L. Serologies for viral hepatitis and HIV were non-reactive; NS1 was non-reactive and dengue serology was non-reactive. During hospitalization, he showed a muscle injury pattern compatible with rhabdomyolysis, with CPK persistently >1,000 U/L (maximum 21,550), transaminases peaking at AST 2,296 and ALT 470, and creatinine rising to 1.14 mg/dL, requiring abundant IV hydration of approximately 4–5 liters per day. Given the clinical picture, a rapid influenza test was performed and was POSITIVE - INFLUENZA A. During hospitalization, he remained hemodynamically stable and afebrile, with laboratory improvement beginning on the fourth day of hospitalization, including a decline in liver enzymes (AST 287 / ALT 257) and CPK 16,910, in addition to normalization of renal function. This case of viral myositis due to influenza A complicated by rhabdomyolysis underscores that respiratory viral infections can present with significant and atypical systemic manifestations, requiring early management to avoid unfavorable clinical outcomes. Such cases are more likely to occur in the community during epidemic and outbreak situations, as observed in this epidemiological period, and need to be highlighted, especially in the complete absence of other more common causes.