Introduction: Acute haematogenous osteomyelitis, whose clinical features may mimic erysipelas, is an uncommon disease in adults.
Observation: A 56 year-old man was hospitalized for a suspicion of leg erysipelas. Oral and intravenous antibiotic therapy was inefficient. Magnetic Resonance Imaging (MRI) of the leg revealed osteomyelitis with subperiosteal abscess. Change of antibiotics and surgical debridement improved the patient's condition.
Discussion: Erysipela is a common disease which most often responds to anti-streptococcal therapy. Unfavourable evolution under antibiotherapy must lead to consider necrotizing fasciitis but also acute osteomyelitis. In these cases MRI is necessary. In our observation, the leg pain which preceded other signs of local inflammation, suggested the existence of primitive bone infection which further diffused in soft tissues, thus explaining the erysipelatoid aspect.