SAPHO syndrome: skin and bone inflammation explained

SAPHO is an acronym for synovitis (joint lining inflammation), acne, pustulosis (pus-filled spots, typically on the palms and soles), hyperostosis (overgrowth or thickening of bone) and osteitis (inflammation of bone). It was described under this name by a group of French authors in 1987, bringing together a collection of skin and bone problems that had been reported separately. A case report and review published in Cureus describes it as an autoinflammatory disease, meaning inflammation driven by the innate immune system rather than by classic autoantibodies.

The exact cause is unknown. Reviews say genetic, immunological and infectious factors have all been proposed, including a possible role for the skin bacterium Cutibacterium acnes (formerly Propionibacterium acnes), but none has been proven as the single cause. It affects adults and children, and is reported mainly in women, with an average age at onset of about 38 years.

The presentation is varied. The Cureus review says that an estimated 60% to 95% of patients also suffer from anterior chest wall syndrome, typically involving the sternum, collarbones and the joints between them, and that axial (spine and sacroiliac) involvement is present in 32% to 52%. Pain and swelling at the front of the chest, sometimes with redness, is the commonest presentation.

Skin involvement usually precedes joint symptoms but can occur at any time. The main skin abnormalities listed include palmoplantar pustulosis, pustular psoriasis, psoriasis vulgaris, severe acne and hidradenitis suppurativa. Some people have long gaps between flares of pain and complete remission in between.

• Pain, swelling or tenderness at the front of the chest, around the breastbone and collarbones.

• Back, hip or sacroiliac (buttock) pain with stiffness.

• Swollen, painful joints such as knees or ankles.

• Pustules on the palms and soles, or severe acne, which may have come and gone beforehand.

• Raised inflammatory markers such as ESR and CRP on blood tests.

There is no single test. Published reports say several sets of diagnostic criteria exist, and that the modified Kahn criteria (2003) are the most frequently used. These pair bone and joint involvement with palmoplantar pustulosis or psoriasis, severe acne, isolated sterile hyperostosis or osteitis, chronic recurrent multifocal osteomyelitis in children or chronic bowel disease, and they exclude infectious osteitis and tumours of the bone. In practice diagnosis rests on the clinical picture, imaging findings and the exclusion of infection, tumour and other rheumatological disease.

Imaging plays a central role. The Cureus review describes chest CT showing chronic osteitis of the sternum and costosternal joints and bone scintigraphy showing the characteristic "bull's horn" or "bullhead" appearance over the front of the chest. MRI and CT may also show sacroiliitis. Blood tests commonly show raised ESR and CRP but autoantibodies such as ANA, rheumatoid factor and anti-CCP are negative, and HLA-B27 is not consistently positive (reported in about 4% to 17%).

A bone biopsy is not routine; the review says it is only performed in atypical forms, in particular to exclude a tumour. Because a published report notes that infections and malignancies may masquerade as SAPHO, careful interpretation by a rheumatologist and radiologist is important. Delay of several years before diagnosis is commonly reported.

There are no randomised trials and no definitive treatment guidelines. Case reports and reviews describe a stepwise approach aimed at controlling pain and inflammation. The Cureus review says that non-steroidal anti-inflammatory drugs (NSAIDs) are the first line of treatment, that tetracyclines and macrolides have been used as an alternative given the possible role of bacteria but that their effect tends to wear off when stopped, and that studies have confirmed the effectiveness of bisphosphonates, steroids, methotrexate and anti-TNF drugs.

A second case report describes the mainstay of treatment as pain and inflammation control with NSAIDs and rescue courses of systemic steroids, with disease-modifying drugs (DMARDs) needed eventually where first-line agents fail or disease is severe. Skin disease is treated alongside by dermatology. All of these decisions are made by a rheumatologist, often with input from dermatology, and drugs such as methotrexate need monitoring.

The condition tends to follow a relapsing-remitting course. The case report in the Cureus literature notes that, despite being chronic and inflammatory, it remains stable in the majority of cases, and that early recognition, timely diagnosis and prompt treatment are the main messages. Because bone changes can lead to fusion or ankylosis over time in some people, as seen on imaging in published cases, ongoing review matters.

Practical measures include pacing, physiotherapy and keeping skin conditions under review. Because pain at the front of the chest can understandably prompt worry about the heart or lungs, anyone with new chest pain, breathlessness or pain spreading down the arm should seek urgent help rather than assume it is SAPHO: call 999 if the pain is severe or comes with breathlessness, sweating or feeling faint.

On the NHS, SAPHO is usually diagnosed by rheumatology, sometimes after referral from dermatology, orthopaedics or after a bone abnormality is found on imaging. Because it is rare, you may be seen in a larger centre or a specialist autoinflammatory clinic.

A private rheumatology opinion can offer a quicker first appointment and imaging. Whichever route you take, make sure your GP receives the letters, and that biologic or methotrexate monitoring is agreed between the prescriber and your GP. We could not find a UK patient information page for SAPHO, so this guide relies on clinical literature; your rheumatologist can provide local advice.