Last revised by Mohd Ashyiraff Ilani Bin Ismail on 5 Nov 2023

Pyknodysostosis, (alternatively spelled pycnodysostosis) also known as osteopetrosis acro-osteolytica or Toulouse-Lautrec syndrome, is a rare autosomal recessive bone dysplasia, characterized 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.

Osteosclerosis with narrowed medullary cavities is the main generalized imaging finding. Long bone fractures are common.  

  • short, stubby fingers

  • partial agenesis/aplasia of terminal phalanges, simulating acro-osteolysis 

  • delayed bone age 

  • marked delay in sutural closure

  • frontoparietal bossing

  • calvarial thickening

  • Wormian bones (lambdoidal region)

  • relative proptosis

  • nasal beaking

  • obtuse mandibular gonial angle often with associated small jaw

  • persistence of primary teeth

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

ακρον (acron) in osteopetrosis acro-osteolytica is Ancient Greek for "at the extremity" and refers to resorption at the distal phalanges as observed in this condition. 

The condition is also known as Toulouse-Lautrec syndrome, named after the famous French artist Henri Marie Raymond de Toulouse-Lautrec-Monfa (1864-1901) who was thought to be afflicted with the disease.

General imaging differential considerations include:

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Cases and figures

  • Figure 1: photograph - Henri de Toulouse-Lautrec
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  • Case 1
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  • 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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