Klinefelter Bone Microarchitecture Evolution with Testosterone Replacement Therapy.

Klinefelter Syndrome (KS) patients, defined by a 47 XXY karyotype, have increased risk of fragility fractures. We have assessed bone microarchitecture by high resolution peripheral quantitative CT (HR-pQCT) at the radius and tibia in young KS patients, naïve from testosterone replacement therapy (TRT). Areal bone mineral density (BMD) and body composition were assessed by dual X-ray absorptiometry (DXA). Total testosterone (tT) was measured at baseline. Bone measurements have been repeated after 30 months of TRT. We enrolled 24 KS patients and 72 age-matched controls. KS patients were (mean ± SD) 23.7 ± 7.8 year-old. KS patients had significantly lower relative appendicular lean mass index (RALM) and lower aBMD at spine and hip than controls. Ten patients (42%) had low tT level (≤ 10.4 nmol/L). At baseline, we observed at radius a marked cortical (Ct) impairment reflected by lower Ct.area, Ct.perimeter, and Ct.vBMD than controls. At tibia, in addition to cortical fragility, we also found significant alterations of trabecular (Tb) compartment with lower trabecular bone volume (BV/TV) and Tb.vBMD as compared to controls. After 30 months of TRT, 18 (75%) KS patients were reassessed. Spine aBMD and RALM significantly increased. At radius, both cortical (Ct.Pm, Ct.Ar, Ct.vBMD, Ct.Th) and trabecular (Tb.vBMD) parameters significantly improved. At tibia, the improvement was found only in the cortical compartment. Young TRT naïve KS patients have inadequate bone microarchitecture at both the radius and tibia, which can improve on TRT.