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Pyknodysostosis

Pyknodysostosis (or osteopetrosis acro-osteolytica) is a rare autosomal recessive bone dysplasia characterised by osteosclerosis and short stature. The condition is also known as Toulouse-Lautrec syndrome, named after the famous French artist who was thought to be afflicted with the disease.

Pathology

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.

Clinical presentation

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

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. 

Plain film/CT
Hands
  • short, stubby fingers
  • partial agenesis/aplasia of terminal phalanges simulating acro-osteolysis
  • delayed bone age 
Cranial and maxillofacial
  • marked delay in sutural closure
  • frontoparietal bossing
  • calvarial thickening
  • wormian bones (lambdoidal region)
  • relative proptosis
  • nasal beaking
  • obtuse mandibular gonial angle often with relative prognathism
  • persistence of primary teeth
Other

History and etymology

Derived from the greek terms pucnos = dense , dys = defective , ostosis = bone condition 

Differential diagnosis

General imaging differential considerations include:

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