DP20: A rare cause of bilateral subungual tumour

Catriona Couper and Freida Shaffrali

NHS Lanarkshire, Airdrie, UK

The subungual space can harbour a multitude of tumours, including both benign tumours (further split into solid and cystic lesions) and malignant tumours, typically melanoma, Bowen disease or squamous cell carcinomas. This case presents a B-cell chronic lymphocytic leukaemia/small lymphocytic lymphoma (CLL/SLL) which was diagnosed after developing bilateral subungual lesions beneath the first toenails bilaterally. A 71-year-old patient was referred in January 2020 after podiatry review with 1-cm bilateral tender, flesh-coloured, soft-tissue swellings beneath both first toenails. They were slowly enlarging for a year before presentation. His past medical history was of noninsulin-dependent diabetes mellitus and hypertension, and he was an ex-smoker. He lived with his wife and was a retired bricklayer. The clinical differential diagnosis was of glomus tumour, subungual exostosis and subungual fibroma, and punch biopsy was arranged urgently. Microscopy showed diffuse, dense infiltrate of small lymphoid cells within the dermal tissue with occasional nucleolated larger lymphoid cells suggestive of proliferation centres. Immunophenotype of the infiltrate was positive for CD20, CD5, CD23, BCL2, LEF1 and lambda, and negative for CD3, CD10, BCL6, CD21, IRF4, cyclin D1 and kappa. This was in keeping with dermal involvement of B-CLL, with no evidence within this sample of grade transformation. As a result, he was referred to haematology for further investigation and management. Full blood count was unremarkable. Bone marrow examination was consistent with CLL/SLL and computed tomography imaging showed no extracutaneous disease. Following multidisciplinary team discussion, he received low-dose radiotherapy in June 2020 (4 Gy in two fractions) and repeated at 2 months. Six months later he was discharged by the clinical oncology team having had an excellent response to radiotherapy, and haematology continue to keep him under review. This case demonstrates an unusual presentation of B-CLL/SLL, which is often diagnosed incidentally with lymphocytosis on full blood count testing, and is more common in older adults, particularly men. CLL/SLL is considered the same disease process, and classification depends on whether the clonal proliferation of cells are found in the bone marrow (CLL) or lymphoid tissues (SLL). It also highlights the importance of histological analysis of subungual tumours such as these, as their natural history often results in the nonspecific finding of nail deformity or destruction. There are very few reports of bilateral subungual tumours; however, this adds to the existing literature with reports of bilateral glomus tumour and subungual exostosis.