Hypopituitarism

The pituitary is a small gland at the base of the brain that acts as the body's hormone conductor, releasing signals that drive the thyroid (via TSH), the adrenal glands (via ACTH), the sex glands (via LH and FSH), growth (via growth hormone) and more. In hypopituitarism, one, several or all of these are deficient. Causes include a pituitary tumour (adenoma) or its treatment (surgery or radiotherapy), injury or bleeding, inflammation, and damage around childbirth. The effects depend on which hormones are lacking: too little ACTH means low cortisol (fatigue, low blood pressure, and a risk of dangerous adrenal crisis in stress or illness); too little TSH causes an underactive thyroid (tiredness, cold intolerance, weight gain); too little LH and FSH lowers sex hormones (low libido, loss of periods, erectile dysfunction, loss of body hair); too little growth hormone reduces muscle and wellbeing in adults. A key feature is that the target-gland hormones are low while the pituitary signals are low or inappropriately normal — the opposite of primary gland failure. It is diagnosed by measuring the pituitary and target hormones together, often with stimulation tests, and treated by replacing the missing hormones.

• ACTH and cortisol — a low cortisol with a low or normal ACTH signals secondary adrenal insufficiency; the most safety-critical deficiency.
• TSH and free T4 — a low free T4 with a low or normal TSH signals central hypothyroidism.
• LH, FSH and sex hormones — low sex hormones with low or normal LH/FSH.
• IGF-1 and growth hormone — assess growth hormone deficiency.
• Prolactin and sodium — may be affected depending on the cause.

• Tiredness and weakness
• Low blood pressure and dizziness on standing
• Cold intolerance and weight change
• Low libido, erectile dysfunction, or loss of periods
• Loss of body hair
• Reduced muscle mass and poor sense of wellbeing
• In a pituitary tumour: headaches or visual changes
• In stress or illness: risk of adrenal crisis (severe weakness, collapse)