There are important reasons why muscle is muscle and bone is bone. Sometimes you need flexibility and strength. Other times you need hardness and structure.
In a rare condition called fibrodysplasia ossificans progressiva (FOP), this system breaks down. Your body’s soft tissues -- muscles, ligaments, and tendons -- turn into bone and form a second skeleton outside your normal one.
As bone takes over, it gets harder or even impossible to move different parts of your body, which affects everyday activities such as eating and talking.
FOP often starts in early childhood. It begins around the shoulders and neck, then works its way down through the rest of the body. As you get older, bone replaces more and more of soft tissue, but how quickly that happens varies from person to person.
What Causes FOP?
A glitch in one of the genes that tells your body how to grow your bones and muscles causes the condition. It’s actually part of normal growth that some soft tissue turns into bone. But with this problem in your gene, bone grows too often and too much.
In most cases, you don’t get FOP -- which is also known as myositis ossificans progressive -- from your parents. That happens sometimes, but more often, there’s a change in your genes during your lifetime that causes it.
Signs and Symptoms
One of the telltale signs is present at birth -- the big toe on each foot is shorter than it should be and is turned toward the other toes. About half the people with FOP also have a similar issue with their thumbs.
The other main sign is bone replacing soft tissue. This usually starts with tumorlike growths on the back, neck, and shoulders. The growths are painful and soon turn into bone. These flare-ups repeat throughout your life and spread to the rest of your body.
It’s not always the case, but very often, an injury or virus triggers a flare-up. This makes it especially hard for people to get any kind of surgery or even an injection before getting a cavity filled.
FOP flare-ups typically last 6 to 8 weeks. They may cause pain and swelling, stiffness in the joints, all-around discomfort, and a low-grade fever.
The condition may cause chronic (ongoing) swelling nearly anywhere in your body. As bone replaces tissue, you lose the ability to move body parts, which makes it harder to:
- Breathe (your lungs can’t fully expand)
- Eat (making it harder to get the nutrients you need)
- Keep your balance
- Walk or sit
For some people, it also leads to curves in the spine, either from side to side or top to bottom.
As your ability to move gets more limited, you’re more likely to get infections in your nose, throat, and lungs. You also have a higher chance of some types of heart failure (when muscles in the heart wall weaken and can’t pump enough blood to your body).
Usually it's found during a physical exam when the doctor looks for the two main signs -- the short and inward-pointing toes and the tumorlike growths on the shoulders, back, and neck.
Your doctor can make sure it’s FOP with a blood test that looks for the glitch in the gene that causes it.
Doctors often mistake it for other conditions. This can be especially harmful to people with FOP because common tests such as a biopsy can trigger a flare-up. It’s most commonly mistaken for:
- Aggressive juvenile fibromatosis, also called desmoid tumors, which is a rare cancer in the tendons and ligaments
- Progressive osseous heteroplasia, another disease where bone forms outside the skeleton
If you think your child has this condition, it can help to talk to a doctor who knows about it.
Is There a Cure?
There’s no cure, and treatment is limited. Medicine, such as corticosteroids, can provide relief from pain and inflammation during flare-ups.
Also, an occupational therapist may be able to help with braces, shoes, and other tools to assist with day-to-day activities.