Legionnaires' Disease Presenting With Erythema Multiforme in an Immunocompetent Patient.

Legionnaires' disease is a severe form of pneumonia most commonly caused by Legionella pneumophila serogroup 1. While primarily affecting the lungs, extrapulmonary manifestations such as hyponatremia, renal dysfunction, and hepatic involvement are well described. In contrast, cutaneous manifestations are rare and remain poorly characterized. We report the case of a 62-year-old immunocompetent man with a history of chronic alcohol use and active smoking who presented with fever, dyspnea, and productive cough. On admission, he was febrile (38.5°C), tachycardic, and had crackles over the right lower lung field. Laboratory evaluation revealed hyponatremia (132 mmol/L) and markedly elevated inflammatory markers (CRP 480 mg/L, procalcitonin 41 ng/mL). Chest imaging demonstrated right lower lobe pneumonia. Initial empiric therapy with amoxicillin-clavulanate was started. Within 48 hours, the patient developed acute respiratory failure requiring intubation and ICU admission. Urinary antigen testing confirmed Legionella pneumophila infection, and antibiotic therapy was switched to levofloxacin and spiramycin. The course was complicated by severe ARDS (PaO₂/FiO₂ ratio 100) requiring prone positioning, and septic shock requiring vasopressors. On day 9 of hospitalization (seven days after targeted therapy initiation), the patient developed a diffuse, non-pruritic erythematous maculopapular rash with targetoid lesions, involving the trunk and limbs, with palmar involvement and petechiae at the ankles, without mucosal involvement. A drug eruption was initially suspected; however, skin biopsy showed mild interkeratinocytic edema with superficial lymphocytic infiltrate and rare keratinocyte necrosis, without eosinophilia or features of toxidermia. Direct immunofluorescence and PCR testing for herpes simplex virus and Mycoplasma pneumoniae were negative. These findings supported a diagnosis of erythema multiforme (EM) secondary to Legionella infection. The rash resolved spontaneously without specific treatment. The patient improved clinically, was extubated on day 12, weaned off vasopressors by day 10, and discharged on day 20 after completing antibiotic therapy. This case illustrates a rare presentation of Legionnaires' disease complicated by EM. Recognition of this association is important, as cutaneous findings may mimic drug reactions and lead to inappropriate modification of effective antimicrobial therapy. This report contributes to the limited literature describing dermatologic manifestations of Legionella infection and underscores the need for clinical awareness of this uncommon presentation.