Borrelial Lymphocytoma of the Ankle: An Unusual Presentation of Lyme Borreliosis.

Borrelial lymphocytoma is an uncommon cutaneous manifestation of Lyme borreliosis and is considered a localized reactive B-cell pseudolymphoma induced by infection with members of the Borrelia burgdorferi sensu lato complex. The condition most commonly affects the ear lobe, nipple-areolar region, and scrotum, whereas involvement of the ankle is rarely reported. We report the case of a 47-year-old man who presented with a persistent erythematous papule adjacent to the lateral malleolus following a tick bite sustained approximately one year earlier. The lesion persisted despite several topical treatments. The patient did not recall a preceding episode of erythema migrans and had no extracutaneous manifestations suggestive of Lyme borreliosis. Borrelia serology performed by enzyme-linked immunosorbent assay (ELISA) revealed positive Borrelia IgG antibodies, which were subsequently confirmed by immunoblot. Histopathological examination of the skin biopsy demonstrated a dense dermal lymphoid infiltrate with reactive lymphoid follicles and numerous plasma cells, findings consistent with borrelial lymphocytoma in the appropriate clinicopathological context. Treatment with doxycycline (100 mg twice daily for three weeks) resulted in marked clinical improvement and near-complete resolution of the lesion within a few weeks. No recurrence was observed during six months of follow-up. This case highlights the rare occurrence of borrelial lymphocytoma involving the lateral malleolus, an unusual anatomical location that may delay diagnosis because of its atypical presentation. It also emphasizes the importance of clinicopathological correlation, integrating the clinical history, serological findings, and histopathological features, in establishing an accurate diagnosis and distinguishing borrelial lymphocytoma from other cutaneous pseudolymphomatous and lymphoproliferative disorders.