The feet demonstrate a prominent hallux valgus deformity with microdactyly, particularly affecting the phalanges. There is partial fusion of the proximal and distal phalanges. There is no evidence of an arthropathy, bone demineralisation or diffuse bone fusion-- features that might suggest JRA. The appearances suggest a congenital aetiology.
In combination these features are characteristic of fibrodysplasia ossificans progressiva.
This disease density is commoner in men and often congenital with variable inheritance (sometimes autosomal dominant), often, probably more often, the disease appears as a spontaneous mutation.
There is a congenital element of great toe (occasionally thumb) microdactyly, synostosis and hallux valgus that occurs in 75-90 % of cases. Even family members unaffected by other features may demonstrate this feature in 5%. Widening of the proximal femoral shaft is a less frequent finding.
Presentation is usually in the first decade of life. The disease process starts in the neck, usually as painful subcutaneous nodules that enlarge progressively, coalesce and secondarily calcify or ossify (not shown in this case). These fibroblastic/myofibroblastic foci may be precipitated as the result of minor trauma or infection. The disease pathophysiology is uncertain but likely reflects abnormal collagen metabolism. Alopecia and are occasionally reported possibly related to a generalized collagen abnormality.
The process extends to the cervicothoracic region and upper arms. Initial presentation is therefore often torticollis. Eventually the pelvis and more peripheral extremities may be involved. Ossification has a characteristic pattern extending cranio-caudally, dorso-ventrally and axio-appendicularly. All smooth muscle structures are spared as are the heart, diaphragm, larynx and sphincters.
The process is generally one of soft tissue calcifications and ossification (tendons, ligaments, fasciae, aponeuroses) causing secondary ankylosis of joints. Hence the term pseudoexostoses, adjacent to joints. The cervical spine is an exception with progressive fusion of the posterior bony elements occurring in the second decade.
Later in the disease fusion of the hip joints renders these patients immobile. Oral intake may be significantly reduced by masseter ossification (especially after dental procedures). Eventually death occurs due to restrictive respiratory failure from soft tissue ossification. However, as the disease demonstrates phenotypic heterogeneity survival in milder forms to adulthood are documented. Soft tissue calcification may be also present in other diseases (calcium disorders, dermatomyositis and calcinosis universalis/ tumoral calcinosis). It is distinguished from these conditions by the absence of trabecular bone formation (ossification). Genuine soft tissue ossification aetiologies (eg. paraplegia and burns) are distinguishable due to the absence of neck and toe involvement.