A rare cause of swelling and limited mobility in the back in a child: a case of fibrodysplasia ossificans progressiva during a flare-up period

Introduction

Fibrodysplasia ossificans progressiva (FOP) is an exceedingly rare and highly disabling genetic disorder with congenital malformations of the big toes and progressive heterotopic ossification (HO) [1]. Prevalence is one in two million individuals. It is typically diagnosed within the first decade of life. FOP is caused by a somatic de novo missense mutation in the activin A receptor type I (ACVR1, also known as ALK-2) gene [2]. As the disease is progressive and disabling in nature, early diagnosis and genetic counseling are necessary. Biopsy should be avoided because it can trigger HO formation and inflammatory processes [3]. Hence, clinical examination and radiological imaging assume a significant role in the diagnostic process.

HO in FOP patients typically begins in the neck and back, eventually spreading to joints such as the shoulders, elbows, hips, knees, and ankles. Usually, the disease affects multiple areas of the body in the third decade of life [4]. Soft tissue swelling and flare-up symptoms, such as swelling, pain, decreased mobility, stiffness, warmth, and redness, can occur due to HO. While some flare-ups resolve, others result in the development of mature heterotopic bone from connective tissues.

Publication History

Received: 18 August 2025

Accepted after revision: 04 November 2025

Article published online:
21 November 2025

• References

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• 2 Pignolo RJ, Baujat G, Brown MA. et al. The natural history of fibrodysplasia ossificans progressiva: a prospective, global 36-month study. Genetics in Medicine 2022; 24: 2422-2433
• 3 de Ruiter RD, Smilde BJ, Pals G. et al. Fibrodysplasia Ossificans Progressiva: What Have We Achieved and Where Are We Now? Follow-up to the 2015 Lorentz Workshop. Front Endocrinol (Lausanne) 2021; 12: 732728
• 4 Pignolo RJ, Bedford-Gay C, Liljesthröm M. et al. The Natural History of Flare-Ups in Fibrodysplasia Ossificans Progressiva (FOP): A Comprehensive Global Assessment. J Bone Miner Res 2016; 31: 650-656
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