A RED HERRING? PAINFUL URTICARIA FOLLOWING AMPICILLIN CONTACT EXPOSURE

Abstract

<h3>Introduction</h3> Acute painful urticaria is often caused by an underlying systemic illness or exposure to a drug or vaccine. Occasionally, no cause is found which prompts consideration of other etiologies. <h3>Case Description</h3> A 22-year-old male nurse with a history of Amoxicillin allergy (delayed-onset exanthematous rash) presented to the ED with an urticarial rash, 48 hours following an accidental ampicillin exposure to his right hand at work. Initial symptoms started 24 hours later with painful swelling of bilateral hands. Despite treatment with prednisone and diphenhydramine, a painful, pruritic urticarial rash developed on his arms, trunk, gluteal cleft, and knees. New onset arthralgias and angioedema prompted presentation to the ED, where he was treated for anaphylaxis and started on intravenous steroids and antihistamines. Initial labs showed a neutrophilic leukocytosis and a mild elevation in CRP. Workup revealed normal complement with negative infectious and rheumatologic evaluations. A punch biopsy showed "perivascular and interstitial neutrophilic infiltrate with few eosinophils," concerning for neutrophilic urticarial dermatosis (NUD) or a serum sickness like drug reaction (SSLR). Seven days after exposure, symptoms began to improve leading to discharge. <h3>Discussion</h3> NUD often occurs in the setting of an underlying systemic disease such as SLE or adult-onset Still's disease. Recently, SSLRs have also been identified as a cause of NUD. SSLRs are not well understood and have not previously been described as systemic contact reactions. Although, ampicillin exposure was thought to be a red herring in this case, further investigation is needed to better understand a potential relationship when another etiology cannot be identified.