SAPHO syndrome

Definition

SAPHO stands for synovitis, acne, pustulosis, hyperostosis and osteitis. This rare syndrome affects bones, joints and skin; the features can occur in any combination. It is most likely an autoinflammatory disease and is closely related to chronic non-bacterial osteitis (CNO) of childhood.

Occurrence & epidemiology

A frequency of about 1 in 10,000 has been reported in the white population; the true incidence is unknown. Mainly people in their third to fifth decades are affected, women more often. In a Japanese survey, over 80% of cases were pustulotic arthro-osteitis, whereas in Israel severe acne was the most common skin manifestation.

Aetiopathogenesis

Multifactorial, involving genetic susceptibility, immune dysregulation and infectious or environmental factors. Neutrophil hyperactivity and raised interleukin-1 levels, among other findings, point to an autoinflammatory origin.

Clinical features

• Bones and joints: sterile osteitis, mainly of the anterior chest wall (sternum, clavicles) with pain, tenderness and swelling; also the axial skeleton, peripheral joints, mandible, long bones and pelvis.
• Skin (in 60–90%): palmoplantar pustulosis, psoriasis vulgaris, severe acne (acne conglobata or fulminans); less often hidradenitis suppurativa, dissecting cellulitis of the scalp and neutrophilic dermatoses.
• Systemic symptoms such as fever, weight loss and fatigue.

Histology

Skin lesions show neutrophilic pseudoabscesses; bone biopsies show sterile osteomyelitis.

Diagnosis

• Suspected when a pustular skin disease is combined with rheumatic pain.
• MRI: inflammation of bone marrow or joints at characteristic sites (clavicle, sternum, pelvis, heel, mandible).
• Laboratory: no specific findings; in active disease raised ESR and CRP, mild leucocytosis and thrombocytosis.
• Validated classification and diagnostic criteria are lacking; diagnosis is often delayed.

Differential diagnoses

• Acne conglobata
• Folliculitis decalvans
• Generalized pustular psoriasis (von Zumbusch)
• Hidradenitis suppurativa (acne inversa)
• Pyoderma gangrenosum
• Acne fulminans
• Furuncle and carbuncle
• Erythema nodosum

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References (selection)

1. DermNet: SAPHO syndrome
2. SAPHO syndrome: current clinical, diagnostic and treatment approaches
3. SAPHO syndrome and pustulotic arthro-osteitis
4. Current and future advances in practice: SAPHO syndrome and chronic non-bacterial osteitis (CNO)

Cross-references