SAPHO Syndrome Presenting With Severe Inflammatory Back Pain (Sacroiliitis) and Rare Retinol Associated Myopathy in an Iraqi Adolescent Male: A Case Report and Literature Review.

SAPHO syndrome is a rare autoinflammatory disorder characterized by synovitis, acne, pustulosis, hyperostosis, and osteitis. Although musculoskeletal and dermatologic manifestations are well recognized, extra-articular involvement remains uncommon, particularly muscular inflammation. We report the case of a 17-year-old male who presented with severe inflammatory low back pain and extensive nodulocystic acne for which he took escalating doses of isotretinoin. Clinical examination demonstrated positive sacroiliac stress tests, proximal muscle myopathy, and dermatologic evaluation confirmed acne conglobata. Laboratory testing revealed markedly elevated inflammatory markers. Magnetic resonance imaging of the sacroiliac joints showed bilateral asymmetric active sacroiliitis, fulfilling clinical criteria for Axial Spondyloarthritis. The infectious and autoimmune workup was negative. The patient responded favorably to isotretinoin withdrawal and immunosuppressive therapy, with sustained remission following steroid withdrawal. This case describes a rare and severe isotretinoin-associated inflammatory myopathy in SAPHO syndrome, highlighting the need to expand the differential diagnosis of myopathy in SAPHO syndrome. It is imperative to exercise caution when prescribing isotretinoin to patients with SAPHO syndrome.