Poster Presentation 33rd ASM of the Australian & New Zealand Bone & Mineral Society 2023
Bone microarchitecture and disorganized bone tissue in a young woman with pycnodysostosis and an atypical femur fracture: A case report (#254)
BACKGROUND: Pycnodystosis (PYCD) is a rare autosomal recessive lysosomal storage disorder, involving a loss of function mutation of the gene encoding cathepsin K (CTSK). The loss of function of this osteoclastic lysosomal protease reduces bone resorption, increases bone mineral density (BMD), but impairs the structure and material properties of bone. This case report demonstrates that bone fragility in a young woman with PYCD, presenting with an atypical femur fracture (AFF), was not explained by changes in bone density but by microarchitectural defects, disorganized bone and microcracks.
CLINICAL CASE:
A 24-year-old woman with PYCD presented with an AFF in 2020 following a long history of prior minimal trauma fractures (MTF). PYCD was diagnosed in childhood and as an adult this patient displayed several signs and symptoms, including, but not limited to: short stature;
dystrophic nails; short fingers; prominent forehead; prognathism, and; a significant history of 10 peripheral MTFs. Her first MTF occurred at 6-years-of-age. No other medical conditions or significant family history were identified. Her parents were consanguineous.
At the time of the AFF, the patient was treatment naïve. Three years prior she gave birth via Caesarean-section and was able to breastfeed her baby for 12 months. Following the AFF, her vitamin D was slightly reduced (45 nmol/L), while P1NP and CTX were high, at 124 ug/L and 518 ng/L, respectively. Other pathology results were unremarkable.
In the year following the AFF, BMD was high at the spine (T-score = +3.3), total hip (+5.4); and femoral neck (+6.7). High-resolution peripheral quantitative computed tomography (HR-pQCT) of the distal tibia detected unexpected cortical lucencies and sclerotic lesions in the trabecular compartment of the distal tibia. Both total and trabecular volumetric BMD (vBMD) were high and trabecular numbers were increased in both the distal radius and tibia. Disorganization analysis using a novel software (ALIGNOGRAM) showed chaotically disorganized femoral shaft with spike shape masses at locations corresponding to a pseudofracture and sclerotic lesions (Fig1).
CLINICAL CONCLUSION
These imaging techniques detected disorganized bone and microarchitectural defects in a treatment naïve patient with PYCD and an AFF. The suppression of bone resorption in PYCD allows the accumulation of microdamage and disorganized bone that produces bone fragility. Antiresorptive therapy should be avoided.
FIGURE
