Fibrodysplasia Ossificans Progressiva

Genetically transmitted malformative syndrome affecting the connective tissue system. It is characterized by malformed big toes that are often monophalangic, mild mental retardation, and intermittently progressive ectopic ossification.

Myositis Ossificans; Münchmeyer Disease.

Incidence is 1:2,000,000 live births and seems to affect both genders equally.

Autosomal dominant. Gene map locus is 4q27-q31.

Results from overexpression of a potent bone-inducing morphogen (bone morphogenetic protein 4) in lymphocytes that is responsible for ectopic osteogenesis.

Mainly clinical, based on the presence of new bone formation in the soft tissue. There is also an increase in alkaline phosphatase during active phase of the disease. Diagnosis established by molecular biology studies (increased levels of bone morphogenetic protein 4 and its mRNA).

Symptoms usually appear around 6 years of age and consist of cartilaginous and osteoid transformation of connective tissue. This ectopic bone formation leads to skeletal muscle mass displacement and serious limitation of joint movement, mainly in the elbow, hip, and knee. There is a characteristic hallux deformity, which consists of shortened and angulated halluces with associated brachymesodactyly. Cervical spine involvement is common, with varying degrees of cervical fusion and the possibility of atlantoaxial subluxation. Temporomandibular joint involvement may occur. Muscles of the face, larynx, eyes, anterior abdominal wall, diaphragm, and heart usually escape involvement. Finally, limitation of rib movement may lead to a restrictive, shallow type of breathing but rarely to respiratory failure, although pneumonia is a common complication. ST-segment changes and right bundle branch block are however often seen.

Obtain an ECG and pulmonary function testing. Also obtain baseline alkaline phosphatase level. Cervical spine radiography to rule out atlantoaxial subluxation should be done preoperatively.

Because of the temporomandibular and atlantoaxial involvement, direct laryngoscopy may be difficult and fiberoptic tracheal intubation may be wise. Positioning of the patient on the operating room table might be more problematic because of the joint limitations. Successful execution of regional techniques may be impossible because of the ectopic bone formation. Also, local trauma may induce more ectopic bone formation. General anesthesia is recommended.

A few patients might be taking corticosteroids and/or warfarin, so steroid coverage may be warranted or vitamin K for reversal of warfarin in major surgery.