The skin lesions in SAPHO syndrome are characterised on skin biopsy by collections of inflammatory cells, known as neutrophilic pseudoabscesses.
Bony involvement mostly affects the breast bone (sternum), resulting in decreased mobility due to pain, tenderness and swelling. The collar bones (clavicles) are also frequently enlarged on X-ray. Bone biopsy also reveals abscesses, known as sterile osteomyelitis.
SAPHO syndrome is classified along three different spectrums.