Classification of Hypothalamic-Pituitary-Gonadal (HPG) Axis Endocrine Disorders

The proper function of the hypothalamic-pituitary-gonadal (HPG) axis is needed for full pubertal development, normal androgen production and full reproductive capacity. Congenital or acquired disorders at any level of this system can produce characteristic signs and symptoms of testosterone (T) deficiency and disrupt fertility. Organic problems at the level of the hypothalamus and/or pituitary can be differentiated from testicular disorders by measurement of serum gonadotrophins (luteinizing hormone and follicle stimulating hormone). Primary hypogonadism results from testicular defects and is evidenced by elevated gonadotrophins, whereas secondary hypogonadism is central in origin and characterized by low (or abnormally normal) gonadotrophins. Epidemiologic studies have demonstrated a progressive decline in serum T with age. However, the increased rates of hypogonadism seen in advanced age primarily relate to obesity and chronic disease burden. Androgen deficiency may result from a wide range of causes including tumours, medications and systemic illness that directly affect the testes or suppress the HPG axis. Regardless of aetiology, untreated hypogonadism has significant negative consequences on health and quality of life. T deficiency not only contributes to poor bone health but is also linked to increased risk for metabolic problems such as the metabolic syndrome and diabetes and has been associated with all-cause cardiovascular mortality. Understanding the pathophysiology underlying hypogonadism is the foundation for appropriately assessing, diagnosing and treating androgen deficiency. This chapter is a mini-review for endocrine nurses providing a summary of disorders affecting the HPG axis with specific attention given to the nursing process in relation to testosterone deficiency.