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

## TL;DR

A young male with knee pain was diagnosed with lupus after initial misdiagnosis, highlighting the importance of considering SLE in atypical cases.

## Contribution

This case report highlights the atypical presentation of SLE in a young male and emphasizes diagnostic challenges in non-typical demographics.

## Key findings

- A 19-year-old male presented with knee pain initially misdiagnosed as patellofemoral chondromalacia.
- ¹⁸F-FDG PET-CT showed hypermetabolic lesions, leading to an SLE diagnosis meeting EULAR/ACR criteria.
- Treatment with hydroxychloroquine improved musculoskeletal symptoms.

## Abstract

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.