Pyknodysostosis
Updates to Article Attributes
Pyknodysostosis, also known as osteopetrosis acro-osteolytica or Toulouse-Lautrec syndrome, is a rare autosomal recessive bone dysplasia, characterised by osteosclerosis and short stature.
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.
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. 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
- 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 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.
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
-<li>"<a title="Bone in bone appearance" href="/articles/bone-within-a-bone-appearance-1">bone in bone</a>" appearance</li>- +<li>"<a href="/articles/bone-within-a-bone-appearance-1">bone in bone</a>" appearance</li>