Paediatric Imaging

Hypophosphatasia

a deficiency of, or low or absent serum alkaline phosphatase, and increased blood and urine levels of excretion of phosphoethanolamine and inorganic pyrophosphate. Three forms are seen in childhood. One is congenital, which may be diagnosed antenatally by noting very poor fetal ossification, a small statured baby with multiple fractures and bowing of the bones (Fig.1). If the child survives to birth the appearances are the same. Radiologically, there is severe osteoporosis, bowed, deformed long bones and fractures.

There is an infantile form in which the child has anorexia, vomiting, failure to thrive, fits, wide cranial sutures, angulated limbs and a bulging fontanelle. Radiologically, there is a severe osteoporosis with delayed bone age, poor ossification of the skull vault, multiple fractures and multiple vertebral collapse.

The childhood form is a less severe form of the other two. Because of the poor bone formation and generalised demineralisation there is delayed onset of walking. This is associated with a myopathy, severe dental caries, multiple fractures and premature loss of the teeth. Radiologically, there is severe osteoporosis, rachitic changes and premature closure of the skull sutures. See birth trauma musculoskeletal

HC

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Fig.1

Radiograph of both lower limbs in an infant born with bowed legs due to hypophosphatasia.
Hypophosphatasia, Fig.1