Towards the definition of disease phenotypes in pediatric SAPHO syndrome: a national multicentric study.

Objectives: To confirm the presence of different disease phenotypes of pediatric SAPHO syndrome (pSAPHO) based on their skin manifestations in a large cohort of Italian patients.

Methods: pSAPHO were enrolled in the Eurofever Registry and the data retrospectively analysed. Patients were divided depending on their skin manifestations into an Acne-Hidradenitis suppurativa (HS) group and a Palmoplantar Pustulosis-Psoriasis Vulgaris (PPP-PV) group and were compared with patients without skin manifestations (chronic non-bacterial osteomyelitis, CNO). Comparison of frequencies between groups was performed by the means of χ2 test or by Fischer's Exact test.

Results: 54 pSAPHO with skin manifestations (35 acne-HS, 19 PPP-PV) were enrolled and compared with 167 CRMO. In the Acne-HS, 82.9% were males, in the PPP-PV, 84.2% were females, while in the CNO group there were no gender differences (p< 0.0001). The 3 groups differed significantly for age at disease onset: acne-HS median 13.3 years, PPP-PV median 10.2 years, CNO median 9.5 years (p= 0.0001). An axial pattern was more frequent in acne-HS (91.4%) and PPP-PV group (89.4%) compared with CNO (46%) (p< 0.0001). Both acne-HS (82.9%), and PPP-PV (63.2%) required more frequently a biologic therapy than CNO (36.8%), but acne-HS presented a refractory skin disease requiring steroids and different lines of treatment, while PPP-PV responded well to biologics.

Conclusions: Our data have identified two different phenotypes of pSAPHO based on skin manifestations, with different sex, age and response to treatments. These two groups have peculiar clinical features different from the CNO group. A new classification encompassing these phenotypes is warranted.