Introduction: Acute febrile neutrophilic dermatosis (Sweet's syndrome) is a condition characterized by the sudden onset of fever, leukocytosis and tender, erythematous, well-demarcated papules and plaques which show dense neutrophilic infiltrates on histologic examination. Two forms have been described: 1 - Classical or idiopathic Sweet's syndrome. 2 - Malignancy associated sweet's syndrome. Adalimumab (Humira®) a monoclonal immunoglobulin directed against TNF-α with documented efficacy in treatment of several autoimmune diseases. Major reported side effects are infections, secondary malignancies, autoimmune processes, neurological side effects and heart failure exacerbation. Case: 22-year-old male with history of Crohn's disease that was diagnosed two months prior to starting Humira. Five days after patient received his second dose of Humira he developed fever, sore throat and rash, he was admitted to an outside facility where his fevers and rash were thought to be caused by Humira and was given clindamycin and Levaquin®, Humira was held and he was discharged home after he felt better. Patient was seen in our gastroenterology clinic about two weeks after the onset of rash where he was noted to be febrile with temperature up to 102 °F, the sore throat and the rash were persistent but were slightly better per the patient's report. On exam, his rash was erythematous, confluent, slightly tender papules, spread all over the body including the face, trunk and extremities. This was biopsied and patient was admitted to the hospital and started on intravenous steroids. Patient was afebrile during the hospital stay, his rash and sore throat improved significantly. Histopathology report was consistent with Sweet's syndrome. Patient was discharged home on a taper of steroids and is doing well since then. Discussion: Sweet's syndrome association with IBD is rare but has been well documented in multiple case reports. However, Sweet's syndrome has never been reported as a side effect of monoclonal antibodies up to our knowledge, and in this case the temporal relationship between the administration of Humira and the onset of rash is highly suggestive of casual relationship, despite the fact that there have been several case reports of efficacy of monoclonal antibodies in the treatment of refractory sweet's syndrome. Similar paradoxical effect of monoclonal antibodies has been observed with psoriasis, since despite the fact that monoclonal antibodies are used to treat psoriasis, several cases of psoriasis have been linked to the use of monoclonal antibodies, no explanation has been found yet.
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