What is SAPHO syndrome? How is it treated?
- S —Synovitis (90% of patients): oligo asymmetric (large > small joints), axial (sternal), and sacroiliac joints (unilateral).
- A —Acne (18%): cystic acne conglobata, acne fulminans.
- P —Pustulosis (66%): pustular psoriasis, palmoplantar pustulosis, or hidradenitis suppurativa.
- H —Hyperostosis: especially of anterior chest wall with sternocostoclavicular hyperostosis.
- O —Osteitis: symphysis pubis, sacroiliitis (33%), spondylodiscitis, anterior chest wall and vertebral sclerosis, more so than long bones.
The name was proposed in 1987 by Chamot et al. because they were impressed by the association of a sterile arthritis (frequently involving the anterior chest) and various skin conditions. Etiology is unclear; however, Cutibacterium acnes (formerly Propionibacterium acnes) as a causative agent has been implicated. HLA-B27 is positive in 13% of cases. Inflammatory cytokines IL-8, IL-18, IL-17, and TNFα are often elevated. It is thought to be an innate immunity-linked autoinflammatory disease. NSAIDs and antibiotics (especially doxycycline) are typically used as first-line therapy. Conventional immunosuppressive drugs, such as methotrexate, sulfasalazine, leflunomide, and cyclosporine, have variable results reported in the literature. Intravenous bisphosphonates, pamidronate in particular, may be an effective treatment for bone and osteoarticular manifestations. Anti-TNF agents, particularly infliximab, have been consistently effective in treating bone and joint symptoms, but not necessarily skin lesions (reports of exacerbation of pustular psoriasis). Newer anti-TNF agents have been used anecdotally with good success and less frequent exacerbation of skin disease.