PD26-11 DIFFERENTIAL EFFECTS OF TESTOSTERONE TREATMENT ON BONE DENSITY AND BODY COMPOSITION IN MEN WITH CLASSICAL VS FUNCTIONAL HYPOGONADISM

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INTRODUCTION AND OBJECTIVE: There are limited data on Testosterone (T) therapy in men with functional hypogonadism (FH) compared to those with classical forms (primary/secondary hypogonadism, PH/SH) regarding bone density and body composition METHODS: Registry data of 2-5 years comprising 189 patients including 67 men with PH (mean age 32.0±10.1 years), 49 with SH (mean age 30.4±9.4 years) and 73 with FH (mean age 44.8±11.6 years) all receiving uniform treatment using intramuscular T undecanoate (1000 mg). All patients received annual assessments of bone density and body composition using dual-energy X-ray absorptiometry RESULTS: Serum T concentrations increased from 6.8±2.7 nmol/L to 18.1±2.9 nmol/L in men with PH/SH and from 7.9±2.5 nmol/L to 17.3±3.2 nmol/L in men with FH. There was an initial difference in bone density between patient groups (T-Score lumbar spine, PH: -1.8±0.3, SH: -2.3±0.4, FH: -1.2±0.3, all p<0.001 vs each other) and (T-Score hip, PH: -1.4±0.3, SH: -1.7±0.4, FH: -1.1±0.3, all p<0.001 vs each other). Body fat content was higher (p<0.001) in FH (38%±10) than in PH (28%±6) and SH (30%±5). Lean body mass was lower in FH compared to PH/SH (p<0.001), respectively. Changes over time using Kaplan-Meier models revealed fundamental differences in inter-individual effects: men with FH were more likely to lose body fat and gain lean mass compared to men with PH/SH (hazard ratio 1.4 [1.2-1.6], p=0.006 and hazard ratio 1.3 [1.1-1.6], p=0.009). A significant increase in bone density was observed for all patient groups (lumbar spine and hip, both p<0.001), albeit the effect was least pronounced in FH and strongest in SH (lumbar spine: p=0.008 and hip: p=0.01, post-hoc tests). Stepwise multiple Cox regression models could attribute these differences to the different baseline characteristics between groups including age and delta T levels. There was no difference between groups for the overall increase in hematocrit. Changes in PSA levels were more likely to occur in FH (hazard ratio 1.4 [1.2-1.6], p=0.004) CONCLUSIONS: This study provides major new findings regarding effects T therapy in different groups of hypogonadal men. Patients with FH experience greater benefits in losing fat mass and gaining lean mass than men with classical forms of hypogonadism, while these have a more pronounced increase in bone density than patients with FH Source of Funding: none