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Pyknodysostosis

Pyknodysostosis (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

Pyknodyostosis 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.

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

Etymology

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

Differential diagnosis

General considerations include

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