Background: Pycnodysostosis is a rare, autosomal recessive disorder caused by loss of function mutation in the cathepsin K (CTSK) gene1-2. Typical features of this sclerosing bone dysplasia include short stature, skull and facial abnormalities and recurrent minimal trauma fractures with supra-normal bone mineral density and poor bone healing.
Case Presentation: A 24-year-old Iranian female, born to consanguineous parents, presented with an atypical femur fracture (AFF). A history of recurrent fractures was reported since the age of 7 involving bilateral tibia, humeral, metacarpal and metatarsal bones. Classical features of pycnodysostosis including short stature (150cm), and typical craniofacial and dental abnormalities were noted. A very high bone density on DXA further supported the diagnosis (femoral neck Z-score +7.0, lumbar spine Z-score +2.9).
Pycnodysostosis is a disease of dysfunctional Cathepsin K, an enzyme produced by osteoclasts and involved in degradation of bone matrix proteins3. Osteoclast dysfunction in this condition leads to reduced bone resorption, hardening of bone with micro-stress accumulation and fractures.
Early detection and diagnosis are beneficial as growth hormone treatment may normalise skeletal proportions and skeletal height if commenced early4. Management is otherwise supportive with environmental and occupational modifications, dental reviews and referral to medical specialists for various complications.
The occurrence of AFF in this condition sheds light on its pathophysiology in patients with osteoporosis on long-term bisphosphonates5. Our patient denied a family history of fracture and genetic testing of this patient is currently underway.
Conclusion: We describe a rare case of pycnodysostosis with multiple skeletal manifestations. Management is largely supportive, but early detection and referral is beneficial.