Sterile multifocal osteomyelitis with periostitis and pustulosis

Sterile multifocal osteomyelitis with periostitis and pustulosis (also known as SAPHO syndrome variant or chronic recurrent multifocal osteomyelitis with pustulosis) is a rare autoinflammatory bone disorder characterized by the combination of sterile (non-infectious) inflammation of multiple bones, periostitis (inflammation of the tissue surrounding the bones), and pustular skin lesions. This condition belongs to the spectrum of autoinflammatory bone diseases and is closely related to SAPHO syndrome (Synovitis, Acne, Pustulosis, Hyperostosis, and Osteitis). The disease primarily affects the skeletal system and the skin. Bone involvement typically manifests as pain, swelling, and tenderness at multiple sites, with the long bones, clavicles, and vertebrae being commonly affected. Periostitis leads to new bone formation and thickening around affected areas. The pustular skin component most often presents as palmoplantar pustulosis, with sterile pustules appearing on the palms and soles. The underlying pathophysiology involves dysregulation of the innate immune system, leading to chronic sterile inflammation. Bone biopsies show inflammatory infiltrates without evidence of infectious organisms, distinguishing this condition from infectious osteomyelitis. The disease follows a chronic relapsing and remitting course. Diagnosis is primarily clinical and radiological, supported by the exclusion of infectious causes. Treatment is largely symptomatic and includes nonsteroidal anti-inflammatory drugs (NSAIDs) as first-line therapy, bisphosphonates (particularly pamidronate), corticosteroids, and disease-modifying agents such as methotrexate or sulfasalazine. In refractory cases, biologic therapies targeting TNF-alpha (such as infliximab or adalimumab) or IL-1 (such as anakinra) have shown benefit. The prognosis is variable, with some patients experiencing prolonged remissions while others have a more persistent course with potential for skeletal complications.

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