LAUSR

Biologic therapies are increasingly used to treat many inflammatory conditions, including skin diseases. Adverse effects include infections, some of which are potentially serious. A 53-year-old male livestock worker with psoriatic arthritis, for which he had been treated with leflunomide (5 years) and certolizumab (2 years), presented with an asymptomatic lesion on the wrist that had appeared 15 days earlier and had not responded to a 1-week course of oral clarithromycin (500 mg/12 h) and topical fusidic acid therapy. The patient reported neither fever nor systemic symptoms. Physical examination revealed an indurated, erythematousviolaceous nodule (2 cm in diameter) with a central crust on the dorsum of the left wrist (Fig. 1). A swab sample was collected from the lesion surface for culture and a skin biopsy was taken for culture and histopathology. The biopsy showed a superficial and deep predominantly neutrophilic inflammatory infiltrate that formed focal dermal abscesses. No nuclear pseudoinclusions were observed. Periodic acid-Schiff (PAS) and silver staining were negative (Fig. 2). The swab culture was negative, but Nocardia brasiliensis resistant to clarithromycin and sensitive to trimethoprim/sulfamethoxazole was isolated from the skin biopsy culture (Fig. 3). A basic battery of tests and pulmonary and brain computed tomography (CT) revealed no findings of note. The patient was diagnosed with localized primary cutaneous nocardiosis. After discontinuing certolizumab treatment, he began treatment with trimethoprim/sulfamethoxazole (80 mg/12 h and 400 mg/12 h, respectively), which resulted in complete lesion resolution in 6 months. Nocardiosis is a rare infection that most often affects immunocompromised patients, and is considered an emerging infectious disease by some authors. Cutaneous nocardiosis accounts for up to 25% of cases and can lead to disseminated disease. It is caused by direct inoculation, mainly by N brasiliensis. The localized cutaneous form can be indistinguishable from other pyodermas and in one third of cases evolves to a lymphocutaneous form, with formation of nodules along the lymphatic pathway. The differential diagnosis includes bacterial (erysipeloid, tularemia, and anthrax), fungal (sporotrichosis), and viral (Orf and milker’s nodules) infections, as well as atypical mycobacterial infections and leishmaniasis. A secondary form of nocardiosis, caused by hematogenous seeding from another focus, can resemble the primary form and can cause