DP23: A histological TRAPP! A case report of cutaneous T-cell-rich angiomatoid polypoid pseudolymphoma

Jawad Khan, Bo Liu, A.-M. Skellett, Leslo Igali and Joe Murphy

NNUH, Norwich, UK

T-cell rich angiomatoid polypoid pseudolymphoma (TRAPP) is a recently described unique form of benign cutaneous pseudolymphoma. It is a novel entity that describes a solitary polypoidal cutaneous lesion mainly in the adult population. Clinically, it can mimic low-grade lymphoma, cutaneous epithelioid angiomatous nodule or vascular proliferative conditions such as haemangioma and pyogenic granuloma. In the English-language literature, only 18 cases have been reported to date. We report a 33-year-old UK-born man, who presented with a 3-month history of a rapidly enlarging, asymptomatic lesion to his left frontal scalp. Clinically, it was an 8 × 5-mm well-defined solitary red nodule with a yellow surface crust. The initial working diagnosis was pyogenic granuloma. The lesion was shave-excised. Histological analysis showed a polypoid lesion containing prominent vascular channels, which were lined by plump endothelial cells. It had a lobular growth pattern that was bordered by an epithelial collarette. In the dermis, numerous plasma cells, histiocytes and lymphocyte were noted. Immunohistochemistry showed a prominent T-cell infiltrate. Subset analysis showed predominantly CD4⁺ cells. Clonality analysis using BIOMED-2 polymerase chain reaction assays showed that the TRG or TRB gene rearrangements were overall polyclonal in this specimen. The immunohistochemistry also highlighted CD31 and CD34 in an organized lobular growth of vessels within this lesion. Further immunohistochemistry performed confirmed a prominent histiocytic component on CD68P and CD163; S-100-stained dendritic cells; and smooth muscle actin was positive in the smooth muscle walls of the vessels. The other work-up tests including full blood count, urea and electrolyte, liver function tests, blood film, lactate dehydrogenase and Borrelia serology were unremarkable. This case was reviewed at the regional lymphoma multidisciplinary team meeting. Based on the clinical findings and investigation results, a diagnosis of TRAPP was made. There has been no sign of recurrence 5 months postshave excision. In the literature, up to a mean of 46 months of follow-up, no reported cases showed any recurrence. Following discussion in the regional lymphoma multidisciplinary team meeting, he was discharged with self-surveillance advice.