SAPHO syndrome (synovitis-acne-pustulosis-hyperostosis-osteitis) is a rare disorder with skin, joint, and bone manifestations. Its etiology is unknown.

The pathophysiology of SAPHO syndrome is not fully understood but is likely multifactorial. Multiple theories have been hypothesized, including immune system dysregulation, infection (Cutibacterium acnes [formerly known as Propionibacterium acnes] has been cultured from some bony lesions), genetic predisposition, or some combination of these factors. While SAPHO syndrome is classified by some as a distinct entity, others view it within the spectrum of autoinflammatory bone diseases. Chronic recurrent multifocal osteomyelitis (CRMO), an erstwhile distinct entity, is now viewed by many as part of the spectrum of SAPHO syndrome.

The prevalence of SAPHO syndrome is estimated to be 1 in 10 000. Most affected patients are between the ages of 30 and 50, although SAPHO syndrome can affect patients of any age. There is a reported female preponderance.

Patients may present with fever and joint pain / tenderness that commonly affects the joints of the anterior chest wall or spine. Early on there is osteolysis and, later, affected areas of bone demonstrate osteosclerosis and hyperostosis. Enthesopathy may be a feature.

Dermatologic manifestations may include palmoplantar pustulosis (among the most common manifestations of SAPHO syndrome), severe acne, or hidradenitis suppurativa. Skin involvement may arise before or after joint involvement, or both may arise simultaneously.

The manifestations of SAPHO syndrome usually have a chronic, relapsing, and remitting course.