SAPHO is an acronym for the following five letters: synovitis, acne, pustulosis, hyperostosis and osteitis. SAPHO syndrome is a chronic disease involving mainly the skin, bones and joints, with hypertrophy and aseptic osteitis combined with different forms of skin damage as the characteristic changes. Clinical manifestations The etiology and pathogenesis of SAPHO syndrome are unknown. The disease is mainly seen in young and middle-aged people, occasionally in children, and can develop in both sexes, with slightly more women than men. The main clinical manifestations of the disease are symmetrical pain in the anterior upper chest wall, restricted movement of the clavicular and shoulder joints, and low back pain and restricted movement of the low back. Involvement of the sternoclavicular and shoulder joints is common, with occasional involvement of small joints of the wrist and hand and foot. There may be increased skin temperature, redness, swelling, tenderness and morning stiffness at the involved joints. In most patients, bone hypertrophy occurs in the sternum, ribs and clavicle of the anterior chest wall. X-ray shows ossification of the rib-clavicular ligament or bone erosion at its attachment point. The absence of rib involvement below sternum 6 is another characteristic of this disease. The second common site of involvement is the spine and sacroiliac joints, with occasional involvement of the carpals and phalanges, with imaging similar to that of psoriatic arthritis. Osteoarthritis is multiple, mainly in the thoracic clavicle, ilium, and spine, with focal osteolysis or a combination of osteolysis and osteosclerosis on x-ray. The presence of this sign helps in early diagnosis. Skin lesions are diverse, with palmoplantar pustulosis being the most common, followed by pustular psoriasis, severe acne on the face and back, common psoriasis, and sweat glands, among others. Skin lesions can occur simultaneously with or before or after osteoarthritic lesions. Nearly 10% of patients may have clinical manifestations of inflammatory bowel disease. In severe cases, local bone hypertrophy may cause pain and edema in the upper chest wall and upper extremities due to compression of adjacent neurovascular structures, i.e. “thoracic outlet syndrome”. ESR and CRP may be elevated during the acute inflammatory phase, and RF and HLA-B27 are often negative. Biopsies from osteitis lesions are granulocytic and polymorphonuclear leukocyte-dominated granulomas with negative bacterial cultures. Diagnosis and Differential Diagnosis The diagnosis of SAPHO syndrome requires the exclusion of bacterial and fungal infections and tumors, so biopsy and culture of the osteitis lesion is particularly important. The diagnosis can be made by the following criteria: (1) hypertrophy of the sternocleidomastoid bone and any of the following three: (1) multiple osteitis without skin lesions; (2) monogenic aseptic osteitis combined with skin lesions such as palmoplantar pustulosis, psoriasis, acne, or sweat glands; (3) acute or chronic arthritis combined with these skin lesions. Treatment Because of the relatively benign course of the disease and its unknown etiology, the current treatment is based on symptomatic therapy. The preferred treatment is non-steroidal anti-inflammatory drugs (NSAIDs); some people with heavy inflammatory reactions and ineffective NSAIDs can be treated with small to medium doses of glucocorticoids for a short period of time; people with significant peripheral synovitis or skin lesions can be treated with methotrexate; people with combined inflammatory bowel disease can be treated with salbutamol. Recent studies have shown that the new generation of diphosphonates, pamidiphosphonates and TNF-α inhibitors, are effective in relieving symptoms.