Objectives: Familial Mediterranean fever (FMF) is the most common autoinflammatory disease manifesting with self-limited recurrent febrile attacks and polyserositis. Acute recurrent monoarthritis is the most common form of musculoskeletal involvement in FMF; however, up to 5% of FMF patients may develop chronic joint diseases including sacroiliitis. It is difficult to distinguish whether sacroiliitis is a musculoskeletal finding of FMF or whether this is the coexistence of two diseases, FMF and SpA. In this study, we aimed to evaluate FMF patients with sacroiliitis, and compare their features with juvenile spondyloarthropathy (SpA) patients, all of whom had sacroiliitis.
Methods: 15 paediatric FMF patients with sacroiliitis and 30 patients with juvenile SpA followed between 2014-2016 at the Department of Paediatric Rheumatology at Hacettepe University, Ankara, were included in the study.
Results: The median (min-max) age at diagnosis of sacroiliitis was 11 (7-15) for FMF+sacroiliitis, and 11.5 (7-16) years for juvenile SpA patients. All patients suffered from hip pain and morning stiffness. Only two FMF+sacroiliitis patients had enthesitis, while nearly half of juvenile SpA patients (46.7%) had enthesitis. Four FMF patients suffered from lower back pain, although none of them had spinal involvement. On the other hand, approximately one third of juvenile SpA patients had spinal involvement. The median white blood cell count, erythrocyte sedimentation rate, and C reactive protein values in FMF+sacroiliitis patients were higher (10.1x103/mm3 vs 7.8x103/mm3, p = 0.002; 41 vs 28 mm/h, p<0.001; 4.6 vs 1.3 mg/dl, p<0.001; respectively) than juvenile SpA patients. HLA B27 positivity was more common in juvenile SpA than FMF+sacroiliitis patients (86.6% vs 26.7%, respectively, p=0.001). The most common MEFV (MEditerranean FeVer) mutation was M694V in FMF patients. All juvenile SpA patients but one were negative for MEFV mutations. One juvenile SpA patient was heterozygous for E148Q.
Conclusions: We demonstrated that paediatric patients with FMF+sacroiliitis showed different characteristics (higher inflammatory markers, less frequent spinal and enthesitis involvement and HLA-B27 positivity) from patients with juvenile SpA. Whether FMF is a triggering factor for SpA or sacroiliitis is a feature of FMF, is still a matter of debate.