With only 1 in 2 million people being affected, FOP is an exceedingly rare disease. Few doctors would encounter it in their education, symptoms are baffling and so unfortunately, it is commonly misdiagnosed.
In FOP patients a lump is commonly misdiagnosed as cancer, aggressive juvenile fibromatosis, lymphedema or soft tissue sarcoma. FOP is exacerbated by soft tissue trauma associated with invasive diagnostic medical procedures. Therefore, catastrophic and irreversible damage can result through the use of intramuscular injections, biopsies and surgeries. Unfortunately this is a common problem for those with FOP.
There are critical differences between FOP and the conditions above. The key is understanding that there is usually an association with malformed big toes, and the rapidly forming soft tissue swellings that form in characteristic anatomic locations. There are some rare variations of FOP that are not associated with malformed toes.
A common misdiagnosis for FOP is aggressive juvenile fibromatosis. This is a benign but highly aggressive condition where connective tissue cells called fibroblasts proliferate in tissue including muscle, tendon, ligament and fascia. These lesions can invade adjacent soft tissue and cause pain and disability. They are often difficult to remove. They often grow slowly and are not associated with the type of swelling seen with FOP lesions, but often the aggressive juvenile fibromatosis lesions do not present until they are fairly large. Thus, many doctors see a soft tissue swelling in a patient with FOP and think it looks like an aggressive juvenile fibromatosis lesion, especially since they arise from similar tissue. If a biopsy is done of very early FOP lesions (fibroproliferative lesions) look like aggressive juvenile fibromatosis under the microscope. However, aggressive juvenile fibromatosis do not progress beyond the connective tissue growth phase, whereas in FOP, they mature through an endochondral process to form cartilage and bone. Once cartilage or bone cells are seen in a lesion, they can no longer be mistaken for aggressive juvenile fibromatosis.
However, the critical information to note is that patients with aggressive juvenile fibromatosis do not have malformed toes. Once again, this is the key!
Visit our video page to find out more about the Issues and Consequence of FOP Misdiagnosis.