Pyknodysostosis, also known as osteopetrosis acro-osteolytica or Toulouse-Lautrec syndrome, is a rare autosomal recessive bone dysplasia, characterised by osteosclerosis and short stature.

Patients present in early childhood with:

– short stature, particularly limbs
– delayed closure of cranial sutures
– frontal and occipital bossing
– short broad hands and hypoplasia of nails
– multiple long bone fractures following minimal trauma

Pyknodysostosis is a lysosomal disorder due to genetic deficiency in cathepsin K which has been mapped to chromosome 1q21. Cathepsin K is essential for normal osteoclast function.

Radiographic features
Osteosclerosis with narrowed medullary cavities is the main generalised imaging finding. Long bone fractures are common. Obtuse angle of the mandible. Lack/abnormal teeth.