The clinical picture of male hypogonadism varies markedly between patients who have yet to undergo puberty and those subjects that have already reached sexual maturity. It behooves the clinician to be astute regarding certain signs and symptoms that occur at each stage of life. In the pubescent male, the most noticeable signs of reduced testosterone are a lack of age-appropriate virilization and a paucity of secondary sexual characteristics, such as deepening of the voice and temporal hair recession [7]. These patients can display sustained height increase (albeit without a pubertal growth spurt) because of a failure of the epiphyses to close, and exhibit eunuchoid body proportions, where arm span is greater than overall height by >2 cm [8].

Hypogonadism in the pubescent male can indicate of a genetic disorder. In these cases, the classic signs and symptoms of these rare disorders can alert the clinician to the presence of a coincident hypogonadal state. In Kallmann syndrome, low serum levels of testosterone result from reduced or absent gonadotropin releasing hormone (GnRH), and juvenile boys may present with anosmia, delayed sexual development, and midline facial/cranial defects [9]. Although Klinefelter syndrome is the most common genetic cause of hypogonadism, patients typically exhibit a clinically normal phenotype until puberty. At which point, serum LH and FSH levels dramatically increase, inhibin B decreases, and testosterone levels fall, leading to hypogonadal manifestations [10]. Pre-pubertal Klinefelter boys have preserved normal seminiferous tubule architecture with characteristically reduced germ cell counts. In contrast, in Klinefelter patients who have undergone puberty, their seminiferous tubules undergo extensive hyalinization and fibrosis with testicular atrophy [10]. Bilateral congenital anorchia is another potential genetically linked etiology of testosterone deficiency that is easily identified by congenital absence of the testes [11].

Patients who have reached sexual maturity exhibit a different constellation of symptoms, mainly centering on a loss of secondary sexual characteristics. Loss of body hair with a reduced frequency of shaving, decreased muscle mass, physical strength, and atrophic testicles are typical examples [2]. According to the Endocrine Society, other specific symptoms of testosterone deficiency include reduced sexual desire and frequency of sexual activity, decreased spontaneous and nocturnal erections, hot flashes, and breast tenderness or gynecomastia [2].

Often, the symptoms of testosterone deficiency are difficult to distinguish from the physiologic changes that we witness with normal aging. Therefore, testosterone deficiency in the aging male is often not recognized [12]. There are also differences in the presentation of testosterone deficiency in middle-aged men from the geriatric population. Many signs and symptoms of testosterone deficiency are expressed heterogeneously with respect to age in the post-pubertal population [13]. In a series of 1,647 males who were assayed for signs and symptoms of testosterone deficiency, the youngest quartile showed an inverse correlation between testosterone and hypoactive sexual desire, while the oldest quartile demonstrated inverse correlations between testosterone and both severe erectile dysfunction and somatized anxiety [13].