It is well established that there is an age-related decline in testosterone production of men, which might play a role in the age-related decline in sexual desire and erections. Such a causal relationship is still debated since few studies found significant relationships between serum testosterone and sexual parameters of aging men that persist after adjustment of the data for age. In addition although 2 meta-analyses of randomized controlled trials confirmed a significant effect of testosterone therapy on sexual desire and erections of men of any age when baseline testosterone is below 12 nmol/l, the effect of this therapy is rather disappointing when it is used in the specific and prevalent population of the men presenting with erectile dysfunction (ED), and who are subsequently diagnosed with LOH.
Several causes may account for this lower success rate: the threshold level of the testosterone activity on sexual desire and erections may be as low as 7 nmol/l in some men. In addition, in men with ED and LOH vascular comorbidities are prevalent and may prevent the effect of testosterone therapy on erections. Lastly the hypogonadism associated with ED may be in some cases a consequence rather than the cause of ED. Even if testosterone therapy may fail to improve erectile function of some hypogonadal ED patients, routine testosterone determination remains mandatory in aging men consulting for ED. Achieving physiologic levels of testosterone is indeed one of the rare opportunities to restore spontaneous erections and save the patient from having to plan sexual activity. In addition restoring testosterone, which is generally low in such patients, is the only way of restoring sexual desire. Replacing testosterone may also improve other symptoms associated with LOH. Lastly a threshold testosterone level appears to be required to achieve full efficacy with PDE5 inhibitors in certain men, although this hypothesis has still to be confirmed.
