Musculoskeletal Imaging

Homocystinuria

a group of disorders characterized by inborn errors in methionine metabolism and presence of excessive homocystine in body fluids. Three different autosomal recessive genetic enzymatic defects have been described, all of which lead to neurologic, ocular and skeletal abnormalities and premature occlusive vascular disease. The most frequent physical finding is bilateral lens dislocations. Spontaneous venous and arterial thromboses are the main cause of morbidity. Venous thromboses frequently involve the mesenteric vessels, vena cava, iliac vessels and pulmonary veins. Many patients with homocystinuria have skeletal abnormalities resembling those of Marfans syndrome. Patients are tall and have disproportionately long extremities, scoliosis, pectus excavatum and joint laxity.

On radiographs, changes in the skull include enlargement of the sinuses, widening of the diploic space, extensive dural calcification and prognathism. In the spine, an increased anteroposterior diameter, posterior scalloping, and biconcavity of the vertebral bodies may be present, and scoliosis and compression fractures may also be seen (Fig.1). Changes in the extremities include dolichostenomelia, osteoporosis and multiple growth recovery lines. Other frequently seen deformities include flattening of the epiphyses, broad metaphyses and varus deformity of the humerus. A characteristic stippled appearance can occur in the growth plate in the distal end of the radius and ulna. Abnormal joint laxity may result in genu valgum deformity and patella alta. In the hands arachnodactyly and carpal deformities may be noted. (See arachnodactyly (III:1), Fig. 1)

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Fig.1

AP (a) and lateral (b) radiograph of the spine demonstrate increased anteroposterior diameter, mild posterior scalloping and biconcavity of the vertebral bodies. Scoliosis and osteporosis are also present.
Homocystinuria, Fig.1 (a)
Homocystinuria, Fig.1 (b)