PA15 A case of ecthyma gangrenosum as the initial presentation of autoimmune neutropenia of infancy

Abstract

Autoimmune neutropenia of infancy (AIN) is a rare disorder marked by immune-mediated peripheral destruction of neutrophils, typically presenting before 15 months of age. While AIN usually follows a self-limiting course, severe infections may occur, necessitating prompt recognition and management. Ecthyma gangrenosum, a necrotizing cutaneous infection most commonly due to Pseudomonas aeruginosa, is typically seen in immunocompromised hosts and is rarely reported as an initial manifestation of AIN. We report the case of a previously healthy 12-month-old boy who presented with a 10-day history of diarrhoea and a 3-day history of rash. Examination revealed superficial perianal ulcers with haemorrhagic crusting and lower-limb erythematous pustules. Investigations showed raised C-reactive protein and white cell count with a normal neutrophil count. A perianal swab detected P. aeruginosa, initially considered a colonizer, while additional wound swabs were negative. The patient was treated for erosive napkin dermatitis and impetigo, and received topical fusidic acid–betamethasone and intravenous flucloxacillin. He had a good response and was discharged on oral antibiotics. However, within a week of completing antibiotics, he re-­presented with new ulcerative lesions, fever, lethargy and tonsillitis. Notably, he was now neutropenic (0.1 × 109 neutrophils L−1). Empiric intravenous piperacillin–tazobactam was started for suspected ecthyma, with tissue culture from skin biopsies later confirming P. aeruginosa infection. Despite adequate antimicrobial therapy, he remained neutropenic, prompting further haematological evaluation. Bone marrow biopsy and gene panel analysis for inherited bone marrow failure and immunodeficiency were normal. However, granulocyte-specific antibodies were detected, supporting a diagnosis of AIN. The patient was commenced on granulocyte colony-stimulating factor (GCSF) with resolution of infection. He remains well on weekly GCSF. This case highlights ecthyma gangrenosum as a potential first presentation of AIN and emphasizes the importance of considering underlying immunodeficiency in infants presenting with atypical or severe cutaneous infections, even in the absence of prior risk factors.