Grab the Bull by the Horns
A 48-year-old woman was evaluated for longstanding intermittent inflammatory back pain and a possible diagnosis of axial spondyloarthritis (SpA). Her history and physical examination were unremarkable. There were modestly increased inflammatory markers (C-reactive protein = 0.5 mg/dL, erythrocyte sedimentation rate = 41 mm/1st h) and negative HLA-B27. Sacroiliitis grade 1 and grade 3 of her left and right sacroiliac joints (SIJs) respectively (Fig. 1A), and marginal and non-marginal syndesmophytes of lumbar vertebrae (Fig. 1B, C) were seen on x-ray examination. Bone scintigraphy showed increased tracer uptake of the right SIJ, the 2nd, 3rd and 4th lumbar vertebra, and also the manubrium and sternocostoclavicular joints (Fig. 1D), forming a “bull-horn” sign that was highly specific for SAPHO syndrome. Chest computed tomography was performed, depicting sternocostoclavicular joint lesions consistent with the diagnosis of SAPHO syndrome (Fig. 1E). Furthermore, T1-weighted and STIR magnetic resonance imaging (MRI) showed inflammatory and fat lesions in the SIJs (Fig. 2A, B), which were suggestive of axial SpA but also may found in SAPHO syndrome, and furthermore in the lumbar vertebral bodies (Fig. 2C, D), findings more typical of SAPHO syndrome.
SAPHO syndrome has a variable presentation, while skin manifestations are not mandatory. SAPHO patients with axial skeletal involvement (spine, SIJs) may have radiological findings resembling those of axial SpA,1 resulting in misdiagnosis, especially if back pain with inflammatory features is the main symptom and skin disease is absent. Grabbing the bull by the horns on bone scintigraphy could be helpful in distinguishing such cases of SAPHO syndrome from axial SpA.