Synovitis, acne, pustulosis, hyperostosis, and osteitis (SAPHO) syndrome is a spectrum of heterogeneous diseases characterized by osteoarticular and dermatological manifestations. Osteitis and hyperostosis are core clinical manifestations in SAPHO syndrome, typically affecting multiple areas and possibly progressing to irreversible osteoarticular damage. Most patients with SAPHO have cutaneous involvement, mainly manifested as palmoplantar pustulosis and severe acne. Systemic manifestations are uncommon but occasionally reported. Epidemiological studies suggest the annual prevalence of SAPHO syndrome varies from 0.00144 in 100,000 in Japanese individuals to fewer than 1 in 10,000 in White individuals. The precise etiopathogenesis of SAPHO remains unclear, but it is generally considered an autoinflammatory syndrome that may be related to various etiologies, such as immune dysfunction, infection and genetic predisposition. Owing to the relapsing–remitting disease course, the goal of management is to improve clinical symptoms and prevent disease progression. Various treatments, including nonsteroidal anti-inflammatory drugs, conventional disease-modifying antirheumatic drugs, bisphosphonates, biologics, and antibiotics, are promising options for alleviating the disease.

SAPHO syndrome is a highly heterogeneous disease with distinct treatment response. We report the largest cohort of SAPHO syndrome and explore its clinical classification with special interest in spinal and sacroiliac involvement. A total of 354 patients with SAPHO syndrome were recruited in Peking Union Medical College Hospital. The demographic, clinical and imaging data were collected at baseline. Spinal and sacroiliac involvement was determined by the co-existence of related symptoms and imaging evidence of lesions in the spine or sacroiliac joints on either bone scintigraphy, CT or MRI. A total of 197 (55.6%) patients were identified to have spinal or sacroiliac involvement. Compared to those without spinal or sacroiliac lesions, these patients were significantly older at onset (38 ± 12 vs 35 ± 10 years old, p = 0.019) but had comparable duration of disease. Therapeutically, patients with spinal or sacroiliac involvement had been treated more aggressively with more frequently prescribed NSAIDs, glucocorticoids, DMARDs, TNF-α inhibitors, and bisphosphonates (all p ≤ 0.001). Nonetheless, greater disease activity was observed for these patients at baseline, supported by both inflammatory markers (ESR and hs-CRP) and visual analog scale (VAS) for pain (all p < 0.001). SAPHO patients with spinal or sacroiliac involvement are older at onset and have greater disease activity despite of more aggressive treatments compared to those without. Stratified management is in urgent need for this rare disease.

To explore the patterns of osteoarticular involvement in SAPHO syndrome. Baseline clinical characteristics and imaging data of 99mTc-MDP whole-body bone scintigraphy (WBBS) were collected from 157 out of 164 patients diagnosed with SAPHO syndrome. The twelve most frequently involved osteoarticular sites were analysed by hierarchical cluster analysis with the Ward minimum-variance method. Three distinctive patterns of osteoarticular involvement were identified: the spinal type (70 patients, 44.6%), with predominantly thoracic, lumbar or sacral vertebral lesions; the costal type (52 patients, 33.1%), with lesions of anterior ribs, particularly the first ribs; and the sternoclavicular type (35 patients, 22.3%), with predominantly sternal and bilateral sternoclavicular lesions, characterized by the typical bullhead sign. Notably, a total of 77 (49%) patients exhibited lesions of ribs on WBBS, of which 61.3% involved the first ribs. Interestingly, patients of spinal type were older at onset of cutaneous manifestations than those of sternoclavicular type (P = 0.036) and costal type (P = 0.035). The disease course was remarkably longer in sternoclavicular type than costal type (P = 0.001) and spinal type (P < 0.001). The osteoarticular involvement in SAPHO syndrome can be categorized as three distinct patterns with different corresponding clinical features. The costal involvement in SAPHO syndrome, which was under-recognized previously, may define a distinct sub-type of the disease.

Whole-body bone scintigraphy (WBBS) and MRI are widely used in assessment of patients with synovitis, acne, pustulosis, hyperostosis, and osteitis (SAPHO) syndrome. However, the value of F-18 fluorodeoxyglucose-positron emission tomography/computed tomography (18F-FDG PET/CT) in SAPHO syndrome was unclear. The aim of this study was to characterize the manifestation of SAPHO syndrome on 18F-FDG PET/CT and explore its relationship with clinical symptoms and WBBS. Twenty-six patients who suffered from SAPHO syndrome and had undergone whole-body 18F-FDG PET/CT were recruited in Peking Union Medical College Hospital from 2004 to 2016. Clinical manifestations and laboratory findings were recorded for all patients. Imaging data on 18F-FDG PET/CT and WBBS were collected and analyzed retrospectively. All the 26 patients (20 females and 6 males) exhibited skeletal abnormalities on 18F-FDG PET/CT. Multiple skeletal lesions affecting the anterior chest wall or spine with low to moderate 18F-FDG uptake and coexistence of osteolysis and osteosclerosis presented as the typical features of SAPHO syndrome. Sixteen (61.5%) patients had abnormal 18F-FDG uptake outside the osteoarticular system. PET scan had moderate to substantial agreement with CT and WBBS in revealing lesions in the anterior chest wall and axial skeleton. Nonetheless, the correlation between increased 18F-FDG uptake and clinical symptoms was weak. SAPHO syndrome exhibits characteristic features on 18F-FDG PET/CT. It showed comparable capacity in revealing skeletal lesions with bone scintigraphy.