Multisuture Craniosynostosis and Papilledema in Pycnodysostosis: A Paradox?

Pycnodysostosis (PYCD) is a rare autosomal-recessive skeletal disorder that typically presents with osteosclerosis of the majority of the postcranial skeleton and osteolysis of the calvarium, manifesting as persistent open cranial fontanelles and widely spaced cranial sutures. Craniosynsostosis in PYCD is a somewhat paradoxical feature, and has only been rarely reported. The authors present a unique case of a 6-year-old girl with PYCD, multisuture craniosynostosis involving the coronal and sagittal sutures, severe obstructive sleep apnoea, and raised intracranial pressure presenting as papilledema. She underwent a frontofacial monobloc distraction advancement which successfully corrected her papilledema and obstructive sleep apnoea. Pycnodysostosis is caused by a loss of function mutation in the CTSK gene that codes for the lysosomal cysteine protease, cathepsin K (CTSK). Loss of CTSK impairs the ability of osteoclasts to degrade bone extracellular matrix. Differences in osteoclast phenotype and extracellular matrix composition between membranous and cartilaginous bone may explain the clinical features of PYCD. Animal model studies suggest that craniosynostosis may arise due to variations in patient genetic background.