A Case of Legionella Disease Mimicking Dermatomyositis

Legionella disease is a severe form of pneumonia that can present with rare extrapulmonary manifestations, potentially leading to diagnostic confusion.We report a 61-year-old man with alcohol dependence and heavy smoking who presented with severe pneumonia and systemic erythema, including seborrheic dermatitis-like erythema on the face, erythematous rashes spreading across the trunk, and livedo reticularis on the lower limbs.Laboratory findings showed markedly elevated ferritin, and computed tomography revealed widespread infiltrates and ground-glass opacities.Although empiric antibiotics were initiated, the presence of atypical cutaneous findings and progressive pulmonary lesions raised suspicion for autoimmune-associated organizing pneumonia, and prednisolone was initiated.The nonspecific cutaneous manifestations raised suspicion for dermatomyositis, but no pathognomonic rashes, such as Gottron papules or heliotrope rash, were observed, prompting further investigation for infection before escalating immunosuppression.A urinary antigen test subsequently confirmed Legionella pneumophila.The patient recovered fully after treatment with levofloxacin.This case highlights that Legionella disease can present with pulmonary and nonspecific cutaneous manifestations that may raise suspicion for dermatomyositis.Clinicians should consider Legionella infection in patients with severe pneumonia and atypical extrapulmonary manifestations, particularly those with relevant risk factors.