ReviewSAPHO: What radiologists should know
Introduction
The association between musculoskeletal and skin lesions has been recognized since the early 1960s and was originally documented by Windom et al. followed by Sasaki who described a case of aseptic hyperostosis of both clavicles associated with pustulosis palmaris et plantaris (PPP).1, 2 SAPHO is an acronym originally coined by Chamot et al. in 1987 to describe “le syndrome acné-pustulose-hyperostose-ostéite” based on the findings of a retrospective national study organized by the French Society of Rheumatology describing 85 patients with musculoskeletal pathology associated with PPP and severe acne.3 Just 1 year later the same authors changed the “S”, turning the acronym into “synovitis, acne, pustulosis, hyperostosis, and osteitis”, which is how it is still known and accepted to date.4 There are now well over 450 published cases of SAPHO in the literature.5 However, the true incidence is thought to be much higher making awareness of the condition, particularly among radiologists, very important.
The importance of this condition is that, being relatively uncommon, the combination of lack of awareness, the presenting age ranging from children to adults, as well as the different stages at which the disease can present, creates a wide spectrum of clinical and imaging features. This is particularly applicable to the spine. This in turn, can make it difficult to differentiate it from more sinister pathology, sometimes leading to unnecessary and potentially mutilating intervention.6
In this review article we present the broad spectrum of radiological appearances of SAPHO along with relevant clinical and pathological features that radiologists should know.
Section snippets
Terminology
“Bilateral clavicular osteomyelitis with palmar and plantar pustulosis”,7 “subacute and chronic symmetric osteomyelitis”,8, 9 “sterno-costo-clavicular hyperostosis” (SCCH),10 “inter-sterno-costo-clavicular ossification” (ISCCO),11 “chronic recurrent multifocal osteomyelitis” (CRMO),12 “arthro-osteitis associated with a follicular occlusive triad” (FOT),13 “acquired hyperostosis syndrome” (AHS),14 and “pustulotic arthro-osteitis” (PAO)15 are but a few of approximately 50 terms used to describe
Clinical features
SAPHO is an uncommon condition the prevalence of which, although estimated at no greater than 1 in 10,000, is probably greatly underestimated.22, 23 It is known to present at any age ranging from childhood to adulthood and is characterized by repeated episodes of remission and recurrences. There is slight female predisposition at all ages.24, 25 It has been predominantly documented in European and Japanese literature suggesting an increased prevalence in these areas, but this may reflect
Imaging features
The radiological appearances of the skeletal manifestations in SAPHO are crucial in the diagnostic process and radiologists play a key role in its early diagnosis.16 When typical imaging features appear at typical sites the diagnosis can be made with relative ease if one is aware of the condition. It is in atypical presentations that the condition may be misdiagnosed.29
Aetiology
The bone changes seen in SAPHO are due to an inflammatory process.13 Multiple aetiological hypotheses have been postulated. These include an infective cause, a genetic cause, an exaggerated inflammatory response, and an association with seronegative spondyloarthropathies. An infective cause is the commonest proposition. It is thought that a disproportionately exaggerated autoimmune inflammatory response, triggered by an opportunistic organism in genetically susceptible individuals leads to a
Pathological features
Aseptic osteitis is the hallmark of SAPHO.2 Histologically the non-specific lesions typically demonstrate inflammatory findings that depend on the phase of disease.12 In the acute phase lesions show neutrophil-predominant inflammation with oedema and reactive bone formation indistinguishable from ordinary bacterial osteomyelitis. As the disease progresses to the intermediate phase, lesions show lymphocyte-predominant chronic inflammation. In the late phase, lesions demonstrate markedly
Diagnosis
SAPHO can be difficult to diagnose. Lack of awareness, its variable clinical presentation, its widespread distribution, the broad spectrum of imaging features and the lack of validated diagnostic criteria can result in diagnostic delay.22, 23 A mean time gap ranging 4.6 to 9.1 years between onset of symptoms and diagnosis is reported.24, 32
Benhamou et al. proposed inclusion and exclusion criteria for the diagnosis of SAPHO. These state that, having excluded an infective cause, palmo-plantar
Treatment
There have been no randomized, controlled trials studying the effectiveness of the various available treatments. Treatment should be symptomatic and should not be driven by the extent of radiological abnormalities.28 It is advised that treatment should be continued until skin lesions clear and imaging appearances of symptomatic osteoarticular sites improve on follow-up.30 MRI can be helpful in assessing response to treatment. Changes such as spondylodiscitis and medullary oedema have been shown
Clinical course
The disease can have a greatly variable course with remissions and relapses.2, 25 In a follow-up of 71 cases, Colina et al. showed that 52% had an acute painful phase lasting more than 6 months, 35% had a relapsing–remitting course, and 13% had a limited single phase disease course lasting less than 6 months. Female gender, anterior chest wall involvement at onset, peripheral synovitis, skin involvement, and raised inflammatory markers were associated with a chronic disease course.24 Maugars
Conclusion
The radiologist plays a pivotal role in the diagnosis of SAPHO and we hope that as clinical radiologists become more familiar with the spectrum of radiological manifestations of SAPHO its true prevalence will emerge. For this to happen, the radiologist needs to take an active role in searching for diagnostic clues to confirm or exclude the diagnosis. However, there will be instances where the general radiologist faced with a case of suspected SAPHO may not feel comfortable making the definitive
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