**7. Diagnosis**

The diagnosis is basically clinical and is complemented by imaging tests. Due to its low prevalence, it is necessary to have a high index of suspicion. The analytical data are usually nonspecific but have value in excluding other pathologies. Mild leukocytosis, anemia, or an increase in inflammatory markers might occur. A simple radiography, bone scan with technetium 99 m, and CT are useful. Simple X-ray is of little use since it is usually normal. Bone scintigraphy provides much information, and the pattern of symmetrical sternoclavicular hypercaptation in "bull's head" (where the sternal manubrium represents the skull and the sternoclavicular joints and the clavicles correspond to the horns) is very typical. CT provides us with a lot of information as it is the technique that best visualizes the joints of the anterior thoracic wall, showing a hyperostosis of this zone.

Biopsy and cultures of the affected joints are reserved for doubtful cases and to rule out other diagnostic possibilities. Imaging allows differential diagnosis with other processes (osteomyelitis, Paget's disease, bone metastases, Tietze syndrome, other spondyloarthropathies).

In some patients, cutaneous manifestations might appear after years of nonspecific joint symptoms, making diagnosis even more difficult.
