Fibrodysplasia Ossificans Progressiva (FOP)

Signs and Symptoms

The hallmark symptom of fibrodysplasia ossificans progressiva (FOP) is a malformation of a newborn's big toe. This malformation, which is apparent at birth, consists of  a short big toe with an abnormal turning of the toe called a valgus deviation.

During early childhood, most of those with FOP form painful fibrous nodules, or tumor-like swellings, over the neck, back and shoulders. These nodules often develop after a child experiences some sort of trauma to the body, such as a bump or fall. Episodes also can occur without any warning or may not occur at all. In most cases, the nodules transform into bone during a process known as heterotopic ossification.

When the body starts to generate new bone, the patient usually experiences a painful flare-up. Tissue swelling, joint stiffness and serious discomfort can occur. Some may have a low-grade fever. Flare-ups can last as long as six to eight weeks. The disease then progresses along the trunk and limbs of the body. These lesions slowly replace the body's muscles with normal-looking bone.

Diagnosis

In most cases, an accurate diagnosis of fibrodysplasia ossificans progressiva (FOP) can be made based on a patient's characteristic malformation of the big toe, in addition to rapidly changing swellings on the head, neck or back.

Due to a lack of knowledge of FOP among doctors, the rate of misdiagnosis of the disease is estimated at 80 percent or higher. These errors in diagnosing FOP have caused pain and suffering for FOP patients and their families worldwide. For instance, misdiagnosis has lead to unnecessary invasive procedures, such as biopsies, as well as permanent complications from medical interventions, including loss of mobility.

Three of the most common misdiagnoses for FOP include cancer; aggressive juvenile fibromatosis, also called desmoid tumors; and progressive osseous heteroplasia, another rare disease characterized by the abnormal growth of bone.

Treatment

Unfortunately, there is no effective treatment for fibrodysplasia ossificans progressiva (FOP). Surgery is not an option for removing the excess bones because surgery often results in more bone formation. And these new bones don't disappear on their own.

The good news is that researchers are investigating FOP and new treatments. For example, a drug is being developed that may help to control bone growth. Medications also are available to help relieve symptoms of FOP, such as pain and inflammation.

Since FOP is a progressive disease, it typically gets worse over time as the patient ages but the rate of new bone formation differs for each person and the disease's progression is generally unpredictable.

Although a person is born with FOP, extra bone may not appear at birth and he or she may go months or years without experiencing a flare-up, which signals the development of new bone.