Pathologic fractures are a complication of pyknodysostosis. On x-ray, bone sclerosis appears during childhood, but neither bone striations nor endobones are seen. The calvaria is not particularly dense, but fontanelles are patent and multiple wormian bones are present. Facial bones and paranasal sinuses are hypoplastic, and the mandibular angle is obtuse. Affected persons are clinically normal, apart from valgus knee deformities, although scoliosis and bone fragility occasionally occur.
Diagnosis usually is made by chance when x-rays are taken for an unrelated purpose.
In contrast to the mild clinical signs, x-ray changes are striking. The long bones are undermodeled and bony cortices generally thin. Tubular bones of the legs have gross Erlenmeyer flask flaring, particularly in the distal portions of the femora. Paranasal bossing develops during infancy, and progressive expansion and thickening of the skull and mandible distort the jaw and face. Bone encroachment leads to entrapment and dysfunction of the cranial nerves, particularly the 7th and 8th.