RESUMO
Empyema necessitatis (EN) is a rare disease, with unknown incidence, which has received little attention from a dermatological point of view but it is essential to recognize it because of the possibility of causing mortality if not treated properly and in time. We report a 32-year-old woman, diagnosed with nervous anorexia, with an enlarging mass on the anterior right thoracic wall. Cultures showed Actinomyces gerencseriae as the main etiological agent of her empyema "necessitatis". She was successfully treated with amoxicillin with clavulanic acid. We found that 1) M. tuberculosis (35%) is still the most frequent agent, but Actinomyces (25%) and MRSA (10%) are becoming more relevant; 2) the most frequent dermatological finding is a subacute erythematous mass on costal wall; 3) new treatments have lowered mortality. Any enlarging and painful subacute thoracic mass with fluctuation should be considered as an EN suspicious lesion and the diagnostic approach must include a chest X-ray to rule out lung infection. Dermatologists should know about this infrequent entity in order to properly identify the potentially life-threatening process under these cutaneous lesions, achieving an early diagnosis and proper treatment.