Pyknodysostosis

Dr Andrew Dixon et al.

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

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.

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

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 radiograph / 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

Derived from the greek terms "pucnos" (dense), "dys" (defective) and "ostosis"(bone condition). 

The condition is also known as Toulouse-Lautrec syndrome, named after the famous French artist who was thought to be afflicted with the disease.

General imaging differential considerations include:


Inborn errors of metabolism
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Article Information

rID: 10290
Section: Pathology
Synonyms or Alternate Spellings:
  • Toulouse-Lautrec syndrome
  • Pycnodysostosis
  • Osteopetrosis acro-osteolytica

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    Figure 1: photograph - Henri de Toulouse-Lautrec
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    Pyknodysostosis
    Case 1
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    Pyknodysostosis
    Case 1
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    Case 1: with trigonocephaly
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    Case 2
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    Case 2
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     Case 3
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    Case 4: probable
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