Teaching Case

Increased bone density in an infant.

Incidental increased bone density is detected in an infant. A complete skeletal outlook is perfomed.

Osteopetrosis is a complex disease of at least four different types; the precocious type, the delayed type, the intermediate recessive type and the form associated with tubular acidosis(1). The precocious type is the most frequent form of osteopetrosis and is an autosomal recessive condition, also called the lethal form. It may be encountered in infancy and childhood and may be fatal in the most severe forms (2,3). The clinical manifestations vary, depending on the severity of the disorder and the ensuing complications. Children demonstrate a facial appearance suggesting a senile expression with flat nose and thick lips. Other clinical manifestations, some of which represent complications include deafness, optic atrophy, hydrocephalus, nystagmus, dental caries, osteomyelitis and fractures. The spleen and liver are enlarged due to extramedullary hematopoiesis. Although mild forms exist, survival beyond middle life is uncommon. Death often occurs because of recurrent infections or hematological complications as leukemia. The delayed type is an autosomal dominant variety also called Albers-schonberg disease. Affected persons may be relatively asymptomatic. The disease may be suspected when a pathologic fracture occurs. In both the benign and severe forms, the radiological features are those of a disseminated overall increase in bone density with obliteration of the normal trabeculae pattern. The affected bones are hard, dense and thick. The medullary cavity is reduced in size with a lack of demarcation between the cortex and the spongiosa. Transverse bands of normal bone density are frequently seen near the ends of long bones and in flat bones, lending a classical appearance of a « bone within a bone ». This pattern is particularly observed in the ribs, innominate bone and the calcaneus .Bone modeling is impaired resulting in the expansion of the ends of long bones. The vertebral bodies tend to be radiodense with a prominent anterior vascular notch. The increased bone density is matched by very dense subchondral areas of sclerosis, leading to a « sandwich vertebra » appearance. The skull changes are variable, with increased density of the basal segments. Sclerotic thickening of the vault of the skull may contribute to overall enlargement of the head. The cranial foramina are small. The maxilla could also be affected and prognatism may develop. Osteomyelitis of the jaw bones may be described. The teeth may be malformed, the mastoid regions and paranasal sinuses might be poorly developed. Despite the radiological appearance of strength, the bones are brittle and fractures may appear especially in the long bones and particularly in the femora. A pathologic fracture may suspect a bone disease and lead to the diagnosis. In the benign type, the radiological appearances are similar to those of the recessive form but are less severe. In the intermediate recessive form; the radiological findings are characterized by diffuse bone sclerosis with normal bone modeling. The variety of osteopetrosis with tubular acidosis is also called « marble brain » and consists of osteopetrosis, cerebral calcifications and tubular acidosis. When overall increased bone density is described in children, the differential diagnosis include idiopathic hypercalcemia, heavy metal poisoning, vitamin A and D poisoning and sclerosing forms of leukemia. In adult, the differential diagnosis suspected are myeloid metaplasia, fluorosis, heavy metal poisoning ,fluorosis, sclerotic metastasis , vitamin A and D poisoning(4).