A rare case of concurrent systemic lupus erythematosus and ankylosing spondylitis: diagnostic challenges and therapeutic management: a case report.

Introduction and importance: Systemic lupus erythematosus (SLE) and ankylosing spondylitis (AS) are common autoimmune disorders presented in a Rheumatology Clinic. However, their co-existence in the same patient is extremely rare. This case denotes the rare occurrence of such including the diagnostic dilemma and possible therapeutic options of the condition. Case presentation: A 54-year-old woman, a known case of SLE under immunomodulator and glucocorticoid therapy, presented to the clinic with persistent low back pain for 1 year. History and physical examination hinted toward the diagnosis of axial spondyloarthritis which was later confirmed by magnetic resonance imaging of hip with bilateral sacroiliac joint thereby refuting differentials of avascular necrosis of hip, osteoporotic vertebral fractures as the possible causes for low back pain. Patient was treated with sulfasalazine for AS along with hydroxychloroquine, prednisolone, and mycophenolate for SLE. Patient reported improvement in lower back pain and increased range of motion of hip joint as well as examination revealed only mild sacroiliac joint tenderness on 3 months follow-up. Clinical discussion: Co-existence of SLE and axial spondyloarthritis is uncommon and often presents as a diagnostic dilemma for the clinicians. Imaging is required to rule out common differential diagnoses. Conventional therapy in form of sulfasalazine can provide relief. Conclusion: This case highlights the rare occurrence of SLE and AS in the same patient and raises awareness to consider axial spondyloarthritis as differential for low back pain in patients of SLE. This case also advocates for the use of conventional drug modifying anti-rheumatic drugs such as sulfasalazine in treating axial spondyloarthritis and urges the readers for further research.