BI28 A wolf in sheep’s clothing: cutaneous lymphoma masquerading as infection

Abstract

Cutaneous lesions in immunocompromised patients present a significant diagnostic challenge. Infection, inflammation and malignancy frequently overlap in clinical and radiological appearance. Maintaining diagnostic vigilance is paramount. A 55-year-old man presented with acute left-sided facial droop and hypercalcaemia. His history was notable for high grade B-cell lymphoma, not otherwise specified, treated with R-CODOX-M, R-CHOP and R-MATRIX. Six months prior to presentation he underwent axicabtagene ciloleucel CAR-T therapy, complicated by prolonged cytopenias and fungal pneumonia. Computed tomography (CT) of the brain on admission demonstrated no acute changes. Lumbar puncture revealed a white cell count > 0.25 × 109 cell  L−1. Flow cytometry confirmed a monoclonal population consistent with central nervous system relapse. Dermatological examination identified a large, fluctuant soft-tissue mass over the right anterior shin, which the patient reported had doubled in size over a 2-week period. The lesion was minimally symptomatic despite being ulcerated. This mass had been documented 3 months earlier. Ultrasound at that time demonstrated multifocal small abscesses. An interventional radiology-guided drain was placed, Enterococcus faecalis was isolated, and linezolid was commenced for an infected collection. Incisional biopsy at the time demonstrated features of a dermal abscess, thought to represent a reactive process secondary to follicular/cyst rupture. During the current admission, positron emission tomography–CT demonstrated increased uptake at the lesion site. Histopathological examination of a 4-mm punch biopsy from the lesion revealed cutaneous involvement by lymphoma. The patient was deemed unsuitable for further disease-modifying treatment and was referred to community palliative care. Cutaneous lesions in immunocompromised patients frequently have overlapping infectious and malignant features, increasing the risk of diagnostic anchoring. In this case, the initial microbiological and histological findings supported infection, but rapid progression and poor clinicopathological concordance warranted re-evaluation. A high index of suspicion for cutaneous malignancy should be maintained even in the presence of positive microbiological findings or initially nonmalignant histology, if clinical concern persists.