Primary Prostatic Lymphoma Presenting as Suspected Complicated Prostatitis

Primary prostatic lymphoma is a rare extranodal non-Hodgkin lymphoma that frequently mimics more common prostatic conditions, leading to diagnostic delay. We report the case of a 50-year-old man with HLA-B27 positive ankylosing spondylitis receiving adalimumab who presented with a six-week history of suprapubic pain, fever, and weight loss. Initial investigations demonstrated a normal prostate-specific antigen (PSA) level and a urine culture positive for Klebsiella species. Computed tomography findings were initially interpreted as severe prostatitis with possible abscess formation. However, persistent symptoms despite antibiotic therapy and subsequent magnetic resonance imaging demonstrated extensive solid infiltrative disease involving the prostate, seminal vesicles, bladder base, and pelvic sidewalls with associated lymphadenopathy, raising suspicion for malignancy. Transperineal prostate biopsy revealed diffuse large B-cell lymphoma (DLBCL), activated B-cell subtype, with immunohistochemistry positive for CD20, PAX5, BCL2, MUM1, and MYC expression, and a Ki67 proliferative index of 80% - 90%. Staging investigations excluded distant extranodal disease, supporting the diagnosis of primary prostatic lymphoma. The patient was referred for haematology management and commenced on rituximab-based chemotherapy. This case highlights the importance of reconsidering the diagnosis in patients with presumed prostatitis who fail to improve with appropriate antimicrobial therapy, particularly when PSA levels remain normal despite extensive prostatic disease.