Applied Radiology Case: Pyle-type Metaphyseal Dysplasia

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Pyle-type metaphyseal dysplasia Adejimi O. Adeniji, MD

CASE SUMMARY

A 3-year-old girl came to the radiology department from the genetics clinic, where she was referred because of widening of the bones in her legs. There was concern that other bones were involved. The patient was delivered by spontaneous vaginal delivery at term, after an uneventful pregnancy and weighed 6 pounds, 12 ounces. She had a history of genu valgum, which was noticed at 13 months of age. Her prior medical and surgical histories were not significant. There was no history of bony fractures, hip dislocation or mental retardation. She had a maternal half-sister who was 12 years old and healthy and the patient also had a younger 2-year-old full sister who had started to show the same signs of widening of the leg bones and genu valgum. There was no history of consanguinity. Her developmental history was also within normal limits. Physical examination revealed her weight to be slightly beneath the 50th percentile and her height was just above the 50th percentile. She had no facial dysmorphism, with no obvious clinodactyly, polydactyly or syndactyly. No dental caries were noted. There was no evidence of scoliosis or platyspondyly.

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FIGURE 1. “Erlenmeyer flask” femoral deformity in the right (A )and left (B) femurs with lateral S-shaped bowing of the right (C) and left (D) tibiae.

IMAGING FINDINGS

Skeletal survey revealed a mildly hyperostotic skull, with mild frontal bossing. There was metaphyseal widening of the long bones. Lateral bowing of the tibiae produced an S-shaped configuration (Figures 1C and 1D). However, the spine was normal (Figure 5). DIAGNOSIS

Pyle-type metaphyseal dysplasia (or Pyle’s disease)

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Differential diagnosis: Chronic anemia (e.g. Sickle-cell disease), osteopetrosis, Gaucher disease and NiemannPick disease. DISCUSSION

Pyle-type metaphyseal dysplasia is an extremely uncommon and rare genetic skeletal disorder inherited in an autosomal-recessive pattern (Gorlin et al. 1970.1 This means that both parents are unaffected, but there is a 25%

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FIGURE 2. Undertubulation of both humeri in their proximal two-thirds.

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FIGURE 3. Undertubulation of the distal two-thirds of the radius and ulna. Incidentally noted, is lucency in the left wrist (right arrow), which could be either due to a vacuum phenomenon or artifactual.

FIGURE 4. Skull radiographs, AP and lateral views. There is mild sclerosis of the skull base with prominence of the frontal bones

chance the affected alleles will pass to a developing embryo and produce the widened biones. The actual gene or genetic defect is unknown, and cannot therefore be tested. The striking radiographic manifestations contrast with the relatively normal clinical features. Genu valgum is the only consistent abnormality.

Pyle first described the skeletal anomaly in 1931. Less than 35 genuine cases have since been reported. Pyle-type metaphyseal dysplasia is clinically, radiographically and genetically distinct from craniometaphyseal dysplasia, a relatively common condition with which it has been confused. Pyle-type metaphyseal dysplasia must

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be distinguished and separated from craniometaphyseal dysplasia, for prognostication, since deafness, facial paralysis and occasional impairment of vision may result from cranial nerve compression in the latter, whereas, they are unusual in the former.1,2 Bone fragility and spinal malalignment or scoliosis is infrequent but are

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FIGURE 5. Normal lateral view of the spine.

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well-documented complications.3,4 Carious and misplaced teeth,4 and patchy sclerosis of the cranial vault with associated moderate supraorbital prominence and prognathism are features that have been reported in Pyletype metaphyseal dysplasia.3 Genetic considerations are also relevant, as craniometaphyseal dysplasia is transmitted as an autosomal dominant, whereas, inheritance in Pyle-type metaphyseal dysplasia is autosomal recessive.5 In Pyle-type metaphyseal dysplasia there are gross abnormalities of the tubular bone modeling, with associated mild sclerosis of the cranium. Prominent radiographic features in the long tubular bones consist of splaying of the metaphyses with relative constriction of the diaphyses. The changes are most obvious in the distal femora, where the appearance has been likened to an “Erlenmeyer flask.” Failure of modeling may also be seen in the short tubular bones, with widening of the medial ends of the clavicles, sternal ends of the ribs and pubic bones.

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CONCLUSION:

In spite of the striking radiographic manifestations, there are a few clinical stigmata and the condition has a benign course. REFERENCES

1.Gorlin RJ, Koszalka MF, Spranger J. Pyle’s disease (familial metaphyseal dysplasia. A presentation of two cases and argument for its separation from craniometaphyseal dyslasia. J Bone Joint Surg Am. 1970;52(2):347-354. 2. Mabille JP, Benoit JP, Castera D. Dysplasie metaphysaire de Pyle. Ann of Radiol (Paris). 1973;16:723-730. 3.Pyle, E. A case of unusual bone development. J Bone Joint Surg Am. 1931;13:874-876. 4.Bawkin, H, Krida, A. Familial metaphyseal dysplasia. American Journal of Diseases of Children. 1937;53:1521-1527. 5. Raad MS, Beighton, P. Autosomal recessive inheritance of metaphyseal dysplasia (Pyle disease). Clin Genet. 1978;14: 251-256.

Prepared by Adejimi O. Adeniji, MD, Divisional Chairman, Pediatric Radiology, John Stroger Hospital of Cook County, Chicago, IL.

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