Background: Progressive osseous fibrodysplasia (Fibrodysplasia Ossificans Progressiva, FOP) is a rare orphan genetic disease caused by a mutation in the ACVR1 gene. FOP can be considered a monogenic autoinflammatory disease with clinical manifestations and immunopathogenesis similar to “classical” rheumatic diseases, particularly spondyloarthritis.

Objectives: To analyze the spectrum of clinical manifestations of FOP, including signs similar to spondyloarthritis, and to evaluate the use of the Janus kinase inhibitor tofacitinib in patients with FOP.

Methods: A retrospective and prospective analysis was conducted on patients with a confirmed diagnosis of FOP from 2020 to 2024. The study included 9 patients (4 boys and 5 girls) aged 2 to 15 years. The analysis focused on the use of tofacitinib in 9 patients with severe FOP.

Results: The diagnosis of FOP was verified in all 9 patients based on the presence of “classical” phenotypic stigmata: malformation of the first toes in 6 (66.6%) patients, malformation of the hands in 5 (55.4%), peripheral osteochondromas in 6 (66.6%), and cervical spine anomalies in all 9 (100%). A mutation in the ACVR1 gene was confirmed in 5 patients. Multiple heterotopic ossifications were identified in 7 (77.7%) patients. The disease presented with significant local inflammatory reactions followed by the formation of heterotopic ossifications. During dynamic observation, signs similar to those of spondyloarthritis were noted, including gradual ankylosis of the zygapophyseal joints and vertebral bodies (sindesmo-phytosis type) and sacroiliitis confirmed by imaging methods, as well as gradual ankylosis of peripheral joints in 77.7% of patients; synovitis of the knee and hip joints was observed in all 9 (100%). Tofacitinib was prescribed to all patients aged 2 to 15 years with continuous recurrence of new FOP nodules and relentless disease progression leading to “steroid dependence.” The duration of tofacitinib therapy ranged from 6 to 12 months, with satisfactory tolerance reported in all patients. After 6 months of treatment with tofacitinib, the number of clinical exacerbations significantly decreased, on average from 7 (in the 6 months prior to treatment) to 0-1. The use of tofacitinib allowed for the cessation of glucocorticoid therapy in all 9 patients. All children were able to halt the progression of heterotopic ossification and achieve an increase in the range of motion in major joints.

Conclusion: The administration of tofacitinib has successfully halted the recurrence of new FOP lesions and restrained the progression of heterotopic ossification.

REFERENCES: NIL.

Acknowledgements: I confirm.

Disclosure of Interests: None declared.

© The Authors 2025. This abstract is an open access article published in Annals of Rheumatic Diseases under the CC BY-NC-ND license ( http://creativecommons.org/licenses/by-nc-nd/4.0/ ). Neither EULAR nor the publisher make any representation as to the accuracy of the content. The authors are solely responsible for the content in their abstract including accuracy of the facts, statements, results, conclusion, citing resources etc.