An Unusual Case of Gonadal Venous Thrombosis Presenting as Fever of Unknown Origin

Gonadal vein thrombosis (GVT) is an uncommon clinical entity typically associated with postpartum or postoperative states. Its occurrence in the context of systemic autoimmune diseases is rare and diagnostically challenging, particularly when presenting as fever of unknown origin (FUO). We report the case of a 39-year-old woman presenting with a six-month history of painful red discoloration of the fingertips, right lower quadrant abdominal pain, and five months’ history of persistent low-grade fever. Initial evaluation revealed systemic symptoms including significant fatigue, weight loss, dry cough, and alopecia. Physical examination showed cervical lymphadenopathy, painful oral ulcers, malar rash, and bilateral lower limb oedema. Laboratory investigations revealed leukopenia, elevated inflammatory markers, hypoalbuminemia with nephrotic-range proteinuria, positive antinuclear antibody (ANA) with high titres, and hypocomplementemia. Imaging identified a right gonadal vein thrombosis and multiple fluorodeoxyglucose (FDG)-avid lymph nodes on positron emission tomography - computed tomography (PET-CT). The clinical picture, combined with serological findings, was consistent with a diagnosis of mixed connective tissue disease with features overlapping systemic lupus erythematosus (SLE) and polymyositis. A secondary antiphospholipid syndrome (APS) was considered likely in the context of thrombosis and positive beta-2 glycoprotein antibodies and anti-cardiolipin antibodies. This case underscores the importance of considering systemic autoimmune diseases in the differential diagnosis of FUO and thrombosis at unusual sites. GVT, though rare, may be the first manifestation of an underlying connective tissue disease or APS, and warrants comprehensive immunological and haematological evaluation.