Synovitis, Acne, Pustulosis, Hyperostosis, and Osteitis Syndrome – A Pictorial Review
The acronym synovitis, acne, pustulosis, hyperostosis, and osteitis (SAPHO) syndrome was coined in 1987 in an attempt to form a unifying diagnosis for a rare group of chronic relapsing, inflammatory osteoarticular disorders with dermatological manifestations. Many different names such as sternocostoclavicular hyperostosis and acne-associated spondyloarthropathy have been used to describe this syndrome. SAPHO can be considered to be on the spectrum of seronegative spondyloarthropathy but with defined cutaneous manifestations, which can show periods of exacerbation and remission, the latter of which may contribute to a delay in the diagnosis.
In children, the disease most commonly presents as a chronic recurrent multifocal osteomyelitis, favoring the long bone metaphysis. However, in adults, the anterior chest wall joints, such as the sternoclavicular and manubriosternal, are most commonly affected [Figures 1 and 2].
The pathogenesis of SAPHO remains obscure but is likely multifactorial likely due to a combination of immunological, infectious, and genetic factors.
In this article, we present multiple cases of SAPHO covering all the modalities of imaging.
SAPHO is a rare disease, with limited data available regarding its prevalence; it is estimated to be 1 in 10,000 in Caucasians.[4,5] There are limited reports of SAPHO syndrome involving other ethnic backgrounds such as in African Americans, Chinese, and Japanese suggestive of a worldwide distribution.[4,5]
Osteoarticular manifestations of SAPHO syndrome are characteristic of the disorder and can occur with or without active dermatologic findings. However, more than 60% of patients diagnosed with SAPHO develop an associated cutaneous manifestation.
SAPHO syndrome can affect patients of any age though the average age onset is between 30 and 50 years old. There is a known female predominance, particularly in patients aged <30 years of age.
Palmoplantar pustulosis is the most common cutaneous manifestation,[7,8] followed by acne involving the chest, back, and face. The time interval between the onset of cutaneous and osteoarticular manifestations is <2 years in approximately 70% of patients. Exacerbations of cutaneous and osteoarticular manifestations are often unrelated.
The affected individual typically presents with osteoarticular complaints. This includes pain, swelling, and restricted movement in the affected joints. Patients may present with single or multiple sites of joint involvement. If there is involvement of the axial skeleton, there may be radicular pain. Vertebral destruction is seen in a minority of severe cases. Fever and fatigue may also be present.
There is no pathognomonic biochemical test for SAPHO. In the assessment of SAPHO, it is important to order a full blood count, liver and renal function tests, inflammatory markers (C-reactive protein/CRP and erythrocyte sedimentation rate/ESR), rheumatoid factor, and HLA-B27 to assess for other disease processes. It is important to note that SAPHO can cause raised inflammatory markers and can co-exist in patients who have rheumatoid or more commonly seronegative spondyloarthropathy. Recent small-scale studies have shown raised complement levels (C3 and C4) and immunoglobulin A levels in some patients with SAPHO syndrome, but these remain casual associations.[11,12]
Imaging plays a key part in determining the diagnosis of SAPHO syndrome. The anterior chest wall followed by the spine and sacroiliac joints is the most common sites of involvement in adults.
Radiographs can remain normal in early disease, but with disease progression, 80% of patients develop radiographic evidence of osteoarticular involvement. Radiographic findings are of hyperostosis, osteolysis, or osteosclerosis.[6,14] In the bone, osteitis generally precedes sclerotic lesions. Joint involvement is often depicted by joint space narrowing, cortical erosions, and periarticular osteopenia. Ankylosis can be present. Established sacroiliitis can be seen and is most commonly unilateral with erosions on the iliac side of the joint; this is in contrast to the bilateral sacroiliac joint involvement seen in typical spondyloarthritis.
Radiographs can underestimate the disease process and so a combination of magnetic resonance imaging (MRI) and computed tomography (CT) is, therefore, utilized for better evaluation.
Magnetic resonance imaging
MRI can detect osteitis (bone marrow edema) not seen on conventional radiographs and also identify subclinical foci of active lesions. The thoracic spine is the most commonly affected site in the axial skeleton [Figures 3].[15,16] Lesions may start at the enthesis and cause osteolysis, synovitis, and eventually ankylosis. There may also be soft tissue involvement adjacent to the bone lesions. Non-specific spondylitis and discitis are also commonly encountered. Lack of abscess formation, sequestra, or paravertebral soft tissue involvement helps differentiate SAPHO from pyogenic spondylodiscitis.
Radionuclide whole-body planar imaging may show focal or multiple sites of tracer uptake which can then be used as an adjunct to perform target radiographs or CT.
The “bulls head sign” corresponds to increased tracer uptake at both sternocostoclavicular junctions. The manubrium sterni is meant to represent the upper skull of the bull, while the inflamed sternoclavicular junctions with the adjacent clavicles form the horns. In a single-center retrospective study over 16 years, the bulls head sign was observed in only 23% of patients who had SAPHO [Figure 4]. The study concluded that though the bull- head sign is characteristic for SAPHO it is not entirely sensitive.
Positron emission tomography
SAPHO syndrome should be considered in adult patients with osteoarticular anterior chest wall or axial skeleton involvement with cutaneous manifestations.
Cutaneous and osteoarticular manifestations do not always coincide; therefore, a thorough history must be sought to assess for cutaneous involvement.
Another diagnosis should be excluded before diagnosing SAPHO. These other diagnoses include infection, inflammatory arthropathy, and malignancy.
Treatment is empirical and aimed at symptom control and modifying the inflammatory process. Nonsteroidal anti-inflammatory drugs (NSAIDs) are the first-line agents [Figure 3]. Antibiotics, corticosteroids, disease- modifying antirheumatic drugs, as well as bisphosphonates and biologics have also been used with variable success. Physiotherapy can also be used as an additional treatment. Surgery is reserved for those whose condition has failed to respond to the aforementioned interventions and in those who a complication has developed (vertebral collapse and deformity and temporomandibular joint ankylosis).
Imaging plays an important role in the diagnosis of SAPHO syndrome; it is important for the reporting radiologist to recognize the common and typical patterns of osteoarticular involvement to be able to suggest the diagnosis in the correct setting [Figure 5]. It is also important to remember that though SAPHO is a distinct clinical syndrome which involves the musculoskeletal and dermatological systems, cutaneous manifestations may not coincide with osteoarticular manifestations. If there is any uncertainty with regard to the diagnosis, a multidisciplinary team approach/discussion should be employed to ensure best patient management.
Declaration of patient consentThe authors certify that they have obtained all appropriate patient consent. In the patient(s) has/have given his/her/ their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.
Financial support and sponsorshipNil.
Conflicts of interestThere are no conflicts of interest.
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