This website is intended for U.S. residents only.
This website is intended for U.S. residents only.


FOP Signs and Symptoms

As Fibrodysplasia Ossificans Progressiva or FOP is ultra-rare,1 most healthcare professionals may not have seen a person living with FOP before in their daily practice and so initial misdiagnosis is common.2

A diagnosis of FOP can be made based on some characteristic clinical signs and symptoms, such as having turned-in great toes and recurring flare-ups. There is also a genetic test for the FOP gene that can provide confirmation of a FOP diagnosis.3,4

Sign or symptom?

A sign is something that can be objectively measured and observed by others. For example, in FOP turned-in great toes or unusual lumps appearing on the head, neck and upper back are considered signs.

A symptom is something that is felt by the individual and may not be apparent to others. It is subjective and may differ from person to person. Examples are pain or feeling of warmth at the site of a flare-up.

signs and symptoms

FOP toes

Shortened turned-in great toes may be mistaken for
bunions (hallux valgus)
but could be a sign of FOP

Short and Turned-in Great Toes

The most classic sign of FOP is having shortened and turned-in great toes at birth or to use medical terminology ‘congenital bilateral great toe malformation’. This makes it look like the great toes are turned inwards towards the rest of the foot and the joints of the great toes stick out.5,6

FOP toes are often mistaken for bunions (hallux valgus).5 Bunions in children are not seen very often,2 as bunions normally appear later in life due to wearing ill-fitting shoes over a long period of time.

Another difference between the turned-in great toes characteristic of FOP and bunions is that bunions do not necessarily form on both feet whereas nearly all people living with FOP were born with a deformity of both great toes. The difference between a bunion and FOP toes can be seen on X-ray imaging.5,7

Swellings, Lumps and Bumps

Painful soft tissue swellings that occur quickly and without any apparent cause could be another sign of FOP known as a FOP flare-up.3 These swellings often start in the upper areas of the body, such as the head, neck and back.3

Soft tissue swellings may be accompanied by redness or a feeling of warmth.10 They may also develop into hard lumps or bumps due to extra bone formation that is characteristic of FOP.11


Swellings or lumps that appear and disappear,
move or change shape could be a sign of FOP


Other Signs and Symptoms of FOP

In addition to turned-in big toes and episodes of soft‐tissue swelling,3 people living with FOP who experience a flare-up may experience episodes of pain, reduced movement, and stiffness.10 There may also be other nonspecific signs of not feeling well such as loss of appetite and lack of energy.10 In infants, a stiff neck due to FOP may result in a baby scooting around on his or her bottom rather than crawling.5,12

Other signs of FOP may include: shortened thumbs, other skeletal malformations of the neck area of the spine,13 hips or legs,4 and loss of hearing that may be due to heterotropic ossification in the middle ear.14

FOP Misdiagnosis

Because FOP is ultra-rare, it is often diagnosed later than it could be. This is because many doctors do not know about FOP and medical textbooks often do not have enough information on it.2

It is commonly misdiagnosed as a disease with similar symptoms, such as cancer, other tumors, bunions or other rare diseases.15,16

Just over half of all people living with FOP are diagnosed with a different disease before they get an accurate diagnosis.15,16 On average, people have symptoms of FOP for 1.5 years and see 3 different healthcare professionals before they are accurately diagnosed.15,16

FOP is not:

  • Cancer15,16

    Soft tissue swellings or unusual hardened lumps or bumps that follow a FOP flare-up may be mistaken for tumors. This can not only cause unnecessary worry but also lead to having procedures that can make FOP worse. This includes having a biopsy taken or surgery to remove a suspect lump.

  • Bunions (hallux valgus)2,6

    The connection between turned-in great toes characteristic of FOP is frequently missed at birth, even though it’s an important early sign of the disease.

  • Ankylosing spondylitis11

    Ankylosing spondylitis which is a chronic inflammatory disease that typically affects the joints of the spine. It can cause severe and chronic pain and, in advanced cases, the joint of the spine joints may fuse together causing the spine to curve and the affected person to bend over.

  • Juvenile fibromatosis12

    Like FOP, juvenile fibromatosis is an ultra-rare genetic disorder. However, unlike FOP it involves connective tissue cells called fibroblasts that can typically grow on the head and neck and can cause pain and eventual disability.

Correct FOP Diagnosis is Important

Getting a diagnosis of FOP is important as it can make a big difference in how you, or your loved one’s, health is managed.2

Knowing it is FOP means that certain activities and inappropriate medical interventions that might make FOP worse can be avoided as much as possible and mean you get the appropriate care.6,13

Care should be taken to avoid anything that might cause trauma or overstretching of muscles as this could cause a FOP flare-up and potentially additional bone to grow.6, 13

Particular procedures to avoid or be cautious about include:4

  • Intramuscular injections

  • Biopsy

  • Surgery to remove lumps or correct bunions

  • Certain dental procedures

  • Traditional physiotherapy, including passive range of motion exercises.

It is important that everyone involved in the care of yourself or your loved one is aware that you have FOP. This includes your dentist as overstretching of the mouth for routine dental procedures can cause extra bone to form in the jaw area if due care is not taken.4

Your care team should also be made aware as routine injections given into a muscle have been shown to cause heterotopic ossification (HO).14

A 2001–2002 survey of IFOPA members found that, as a result of being misdiagnosed:2

  • 67% had surgery that was not needed
  • 68% received medication that they did not need
  • 49% had permanent loss of movement due to a treatment that resulted in new bone formation

Do You Suspect FOP?

If you think that you or a loved one might have FOP, please make an appointment with your doctor to discuss your concerns.

Before your appointment you may find it helpful to note down any signs or symptoms that you have noticed such as turned-in great toes or any unusual swellings, lumps or bumps, particularly if these are red or warm to the touch. You may find it helpful to take photographs of the affected areas along to the appointment.

You can also download our conversation starter “Let’s Talk FOP” which contains some key information to remember about FOP and some opening questions that may help with your discussion.

A list of FOP experts is available on the International Clinical Council on Fibrodysplasia Ossificans Progressiva (ICCFOP) website.

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Please always consult a healthcare professional if you require healthcare advice or if you have any specific concerns regarding Fibrodysplasia Ossificans Progressiva. The information provided here is not intended to replace professional advice. This website has been developed by Ipsen in collaboration with those living with Fibrodysplasia Ossificans Progressiva and the healthcare professionals who care for them. Ipsen would like to thank everyone for their valuable insights and stories. All names used on this website are not necessarily real names. Visit our website for more information about us, or to contact us directly. Website design and development by Kanga Health Ltd. Website reference NON-US-001996 December 2020