Fibrodysplasia ossificans progressiva (FOP), previously known as myositis ossificans progressiva (MOP) and also known as Münchmeyer disease and stone man disease (though, as below, there is no sex predilection), is a rare, inherited disorder characterized by progressive fibrosis and ossification of muscles, tendons, fasciae, aponeuroses, and ligaments of multiple sites. It is disabling and ultimately fatal.
Fibrodysplasia ossificans progressiva should not be confused with myositis ossificans circumscripta, which is usually post-traumatic.
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Epidemiology
Fibrodysplasia ossificans progressiva is a very rare disease, with an estimated prevalence of ~1 per 2 million. There is no racial/ethnic, or gender predilection 3. The process and symptoms of heterotopic ossification start between 2 and 5 years old.
Pathology
Most cases arise from sporadic mutations, although some are inherited in an autosomal dominant fashion 3.
Radiographic features
Fibrodysplasia ossificans progressiva can be evaluated using plain radiographs, CT and/or MRI. MRI is mostly useful for more subtle edema which would not be seen on the other modalities. Characteristic features include:
monophalangic first toe
shortened metacarpals
pseudoexostoses (ossification of ligamentous insertions)
microdactyly of the first metacarpal/metatarsal
neck muscle edema
C2-C7 facet joint fusion
Treatment and prognosis
This is a progressive, fatal disease with the median survival being 45 years.
Differential diagnosis
Since the process of heterotopic ossification is quite unique, differential diagnosis on a long term basis is quite limited. However, for punctual abnormalities, the following differential diagnosis should be considered:
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