Diagnosing the SAPHO syndrome: a report of three cases and review of literature

SAPHO, an acronym for synovitis, acne, pustulosis, hyperostosis and osteitis, is a heterogeneous entity with myriad presentations and features overlapping with other entities. It is a differential in patients presenting with skin and bone symptoms, either singly or in combination. Often misdiagnosed radiologically as a malignancy or infection, the diagnosis is seldom thought of. We present three cases referred to us for evaluation of findings unrelated to the presenting symptoms. After evaluation, a ⁹⁹Tc bone scan was ordered, which showed the ‘bull’s head sign’ in all the three cases, confirming the diagnosis. We review the literature for SAPHO. It has a few features which point to its diagnosis and can help us to distinguish it from other seronegative arthritis. The clinician should be aware of this entity and should not hesitate to order a ⁹⁹Tc bone scan. We conclude that SAPHO is not rare, but rather, it is underdiagnosed. High index of suspicion is necessary for diagnosis. A ⁹⁹Tc bone scan is diagnostic and should be ordered in patients having any of the presenting features of the syndrome. We put forward the suggestion of using ⁹⁹Tc bone scintigraphy to define a ‘pre-MRI’ stage of ankylosing spondylitis.