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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
Cranial and maxillofacial
marked delay in sutural closure
Wormian bones (lambdoidal region)
obtuse mandibular gonial angle often with associated small jaw
persistence of primary teeth
vertebral body sclerosis
increased lumbar lordosis
vertebral segmentation anomalies particularly upper cervical (C1 and C2) and lower lumbar (L5 and S1)
History and etymology
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: