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.
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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
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.
Radiographic features
Osteosclerosis with narrowed medullary cavities is the main generalized imaging finding. Long bone fractures are common.
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
- vertebral body sclerosis
- increased lumbar lordosis
- vertebral segmentation anomalies particularly upper cervical (C1 and C2) and lower lumbar (L5 and S1)
- hypoplastic clavicles
- erosion of distal clavicles
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.
Differential diagnosis
General imaging differential considerations include:
-
osteopetrosis
- "bone-in-bone" appearance
- no delayed closure of cranial sutures
- no phalangeal or clavicle hypoplasia
- other sclerosing bone dysplasias
