Table 2.

Classification of hypogonadism and common causes of primary and secondary hypogonadism.

Central Hypogonadism		Primary Hypogonadism
Functional	Organic
• Chronic illness • Malnutrition • Excessive exercise • Stress • Drugs (e.g. opioids, anabolic steroids, glucocorticoids) • Alcohol and marijuana abuse • Other endocrine disorders (e.g. hyperprolactinemia, hypothyroidism) • Severe obesity • Some sleep disorders (e.g. OSAS) • Organ failure (kidney, heart, and lungs)	• CHH (normosmic CHH; Kallmann’s syndrome) • CHARGE syndrome • CHH with CAH • MPHD • Hypothalamic-Pituitary region lesions (e.g. craniopharyngioma) • Metabolic diseases (e.g. hemochromatosis) • Hypophisitis • Infiltrative diseases • Thalassaemia • Infections • Inflammatory diseases (e.g. Langerhans Cell Histiocytosis) • Granulomatous disease (e.g. sarcoidosis) • Iatrogenic causes (e.g. radiotherapy) • Other genetic syndromes (e.g. Prader-Willi, Laurence Moon Biedl etc)	• Klinefelter syndrome • Tuner syndrome • Anorchia • Enzymatic defects • DSD (e.g. gonadal dysgenesis) • LH/FSH resistance • Acquired forms (e.g. chemo- and/or radiotherapies, androgen synthesis inhibitors, autoimmune diseases, end stage renal disease, trauma, gonadal torsion, varicocele) • Advanced age
	Frequencies
20% Male 20% Female	10% Male 20% Female	5-10% Male 25% Female

CHH, congenital hypogonadotropic hypogonadism; CAH, congenital adrenal hypoplasia; MPHD, multiple pituitary hormone deficiencies; DSD, disorders of sexual development.