Coexistence of familial Mediterranean fever with sacroiliitis and Behçet's disease: a rare occurrence.

Familial Mediterranean fever (FMF) and Behçet's disease are relatively rare but may still coexist in the same patient. Sacroiliitis is another feature whose significance is controversial in either of the diseases. We report a case of longstanding FMF with sacroiliitis who later developed typical characteristics of Behçet's disease. Although occurrence by chance cannot be ruled out, this unusual patient may enhance the claims that FMF and Behçet's disease have common aetiopathogenetic mechanisms. It would be appropriate to include this coexistence in the list of differential diagnoses of the two diseases.