Fibrodysplasia ossificans progressiva (FOP) is an extremely rare genetic skeletal disorder manifesting progressive heterotopic ossification, initiating in childhood, often following soft tissue swelling called “flare-ups”. Heterotopic ossifications cause limitation of motion and deformities in the trunk and extremities, and can lead to limitation in activities in daily living including ambulation. The objective of this study is to identify factors affecting ambulatory decline in patients with FOP.
We reviewed medical records of patients with typical form of FOP who visited our department from 2006 to 2018. We found 23 patients in all, and 20 had received gene analysis and typical R206H mutations had been found in all of them. Among the 23 patients, 14 were followed beyond 16 years of age and we classified them into Maintenance Group (MG: ambulation was maintained through the follow-up period) and Decline Group (DG: ambulation declined at least one level in Hoffer’s classification). Age at initial flare-up, age at diagnosis, degree of trunk deformity, and joint contractures in lower extremities were compared between these groups.
MG and DG included seven patients respectively. Ages at initial flare-up and diagnosis did not differ significantly, though initial flare-ups occurred relatively early in DG (mean age 4.1 years in DG and 8.4 years in MG). Four out of seven patients showed moderate-to-severe trunk deformity in both groups. Joint contractures in lower extremities, especially in the hips and knees, were severe in all patients in DG, and mild-to-moderate in all patients in MG.
Patients with typical form of FOP whose ambulation declined around adolescence experienced initial flare-ups in relatively early age, and showed severe joint contractures in lower extremities, as compared with those who maintained ambulation. The degree of spinal deformities did not affect the ambulatory decline.