Lupus-Associated Knee Pain: An Atypical Presentation of Systemic Lupus Erythematosus in a Young Male.

Systemic lupus erythematosus (SLE) predominantly affects young women, and its presentation in male patients may be diagnostically challenging. We report a case of a 19-year-old male presenting with bilateral inflammatory knee pain initially interpreted as patellofemoral chondromalacia. ¹⁸F-fluorodeoxyglucose positron emission tomography-computed tomography (¹⁸F-FDG PET-CT) revealed multiple symmetric hypermetabolic osteo-medullary and subcutaneous lesions suggestive of systemic inflammation. Further evaluation demonstrated non-scarring alopecia, subcutaneous plaques, leukopenia, hypocomplementemia, and positive antinuclear antibodies (ANA), meeting the 2019 European Alliance of Associations for Rheumatology (EULAR)/American College of Rheumatology (ACR) criteria for SLE. Hydroxychloroquine initiation led to improvement in musculoskeletal symptoms. This case illustrates the importance of considering SLE in atypical demographics and in patients presenting with unexplained inflammatory musculoskeletal complaints.