The most common presenting symptoms of flare-ups are swelling, pain, or decreased mobility. Flare-ups may occur at the head, neck, back, chest, the elbows, wrists, fingers, hips, ankles, and feet. There seems to be a shift location with age (Pignolo 2016). Usually loss of functional will follow a flare-up. Still, there may be progression of FOP without obvious flare-ups. 

Ossification of chewing muscles may cause serious eating problems.

Short-term glucocorticoids are reported as a treatment for flare-ups, with a variable result. More research is needed on the effects of glucocorticoids on flare-up as well as other treatments to prevent ossification.

As the extra-skeletal bone formation is accelerated by trauma (including intramuscular injections). Individuals with FOP should at all times prevent even small trauma.

Special attention for all healthcare professionals:

PLEASE follow the IFOPA emergency guidelines at all times. If time permits, consult a specialist regarding potential risks of any surgical or medical interventions being considered.

In general :

Avoid deep tissue trauma: including intramuscular (IM) injections, if possible. Avoid I.M. vaccinations as performed in national prevention schemes. Administration of medicine by venipuncture, subcutaneous and intravenous meds is the alternative When intubation necessary: protect jaw and get expert anesthesia assistance since the jaw and neck may be completely or partially locked.

Bone formation in FOP is episodic, but disability is cumulative. Most patients with FOP are confined to a wheelchair by the third decade of life and require lifelong assistance in performing activities of daily living. Severe weight loss may result following ankylosis of the jaw. Pneumonia or right-sided heart failure may complicate rigid fixation of the chest wall. The severe disability of FOP results in low reproductive fitness and fewer than ten multigenerational families are known worldwide. The median age of survival is approximately 40 years, and death often results from complications of thoracic insufficiency syndrome.

From:

THE MEDICAL MANAGEMENT OF FIBRODYSPLASIA OSSIFICANS PROGRESSIVA: CURRENT TREATMENT CONSIDERATIONS

The International Clinical Consortium on Fibrodysplasia Ossificans Progressiva1 May 2011 From The Center for Research in FOP and Related Disorders, The University of Pennsylvania School of Medicine, Philadelphia, PA 19104