A Rare Presentation of chronic lower back ache radiating to lower limb in a patient with Ankylosing Spondylitis with Andersson Lesion managed by Methotrexate: A Case Report

Introduction : Ankylosing spondylitis (AS) is a chronic inflammatory disorder primarily affecting the axial skeleton, leading to lower back pain, stiffness, and progressive spinal immobility. A rare but serious complication is the formation of Andersson lesions—aseptic, destructive discovertebral abnormalities that can mimic infectious spondylitis. Case Presentation : We report the case of a 25-year-old male with chronic lower back pain radiating to the left lower limb. MRI revealed a focal hyperintense lesion at the lower endplate of the D3 vertebra, sacroiliitis, and edema in the sacroiliac joints—findings consistent with an Andersson lesion. Laboratory results showed positive Human Leukocyte Antigen B27 (HLA-B27), elevated C-reactive protein (CRP), and negative antinuclear antibody (ANA). The patient was treated with nonsteroidal anti-inflammatory drugs (NSAIDs) and methotrexate (MTX), a disease-modifying antirheumatic drug (DMARD) not typically used for axial AS. Over three months of MTX therapy, the patient showed substantial symptomatic improvement. Bath Ankylosing Spondylitis Disease Activity Index (BASDAI) scores progressively decreased, and inflammatory markers normalized. Conclusions : Although methotrexate’s role in axial AS remains controversial, this case demonstrates its potential efficacy in managing rare complications such as Andersson lesions. The positive therapeutic outcome highlights the importance of individualized treatment approaches and supports the need for further research into the broader use of DMARDs in complex AS presentations.