Revision 16 for 'Pyknodysostosis'

Pyknodysostosis (osteopetrosis acro-osteolytica) is a rare autosomal recessive bone dysplasia characterised by osteosclerosis and short stature. The condition is also known as Toulouse-Lautrec syndrome, named after the famous French artist who was thought to be afflicted with the disease.

Pathology

Pyknodyostosis 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.

Plain film / 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

• sclerosis of vertebral bodies
• increased lumbar lordosis
• vertebral segmentation anomalies particularly upper cervical and lower lumbar
• hypoplastic clavicles
• erosion of outer end of clavicles

Etymology

Derived from the greek terms pucnos = dense , dys = defective , ostosis = bone conditiion 

Differential diagnoses

• osteopetrosis
  • no delayed closure of cranial sutures
  • no phalangeal or clavicle hypoplasia
• other sclerosing bone dysplasias