Write a short note on hypopituitarism and Sheehan's syndrome.

Definition

Hypopituitarism is deficiency of one or more anterior pituitary hormones; panhypopituitarism denotes deficiency of all. Posterior pituitary failure causes cranial diabetes insipidus, and typically indicates hypothalamic or stalk involvement rather than isolated anterior gland disease.

Causes

• Tumours: pituitary adenoma (commonest), craniopharyngioma, meningioma, metastases.
• Vascular: Sheehan's syndrome, pituitary apoplexy (haemorrhage or infarction into an adenoma).
• Iatrogenic: pituitary surgery, cranial radiotherapy.
• Infiltrative and inflammatory: tuberculosis (important in India), sarcoidosis, haemochromatosis, histiocytosis, lymphocytic hypophysitis (postpartum, and with immune checkpoint inhibitors).
• Traumatic brain injury and subarachnoid haemorrhage — frequently overlooked causes.
• Congenital: Kallmann syndrome, genetic transcription factor defects, empty sella syndrome.

Order of Hormone Loss

With progressive compression, hormones are characteristically lost in a typical sequence — a favourite examination point:

GH → LH/FSH (gonadotrophins) → TSH → ACTH → prolactin

(A useful aide-memoire: "Go Look For The Adenoma".) Prolactin is usually the last to fall, and may instead RISE because of stalk compression interrupting dopamine inhibition.

Clinical Features BY Hormone

Sheehan's Syndrome

Definition: postpartum hypopituitarism caused by ischaemic necrosis of the anterior pituitary, following severe obstetric haemorrhage with hypotension. It remains an important and under-recognised condition in India, where home deliveries and delayed management of postpartum haemorrhage persist.

Why the pituitary: during pregnancy the anterior pituitary undergoes lactotroph hyperplasia and enlarges by up to twofold, increasing its metabolic demand, while its blood supply through the low-pressure hypophyseal portal system remains unchanged. This makes it uniquely vulnerable to hypotension. The posterior pituitary, with a direct arterial supply, is usually spared — which is why diabetes insipidus is uncommon.

Clinical features:

• Failure of lactation after delivery — the earliest and most characteristic feature.
• Failure of resumption of menstruation (amenorrhoea) after delivery.
• Loss of axillary and pubic hair; genital and breast atrophy.
• Progressive fatigue, weight loss, cold intolerance, constipation, dry skin, pallor — features of secondary hypothyroidism and adrenal insufficiency.
• Presentation is often delayed by years to decades, with the diagnosis made only when the patient presents with unexplained fatigue, hyponatraemia, hypoglycaemia or an adrenal crisis during an intercurrent illness. A careful obstetric history is what makes the diagnosis.
• Acute presentation with hypotension, hypoglycaemia and hyponatraemia in the immediate postpartum period also occurs.

Investigations

• Basal hormones — measure the target gland hormone WITH its trophic hormone: free T4 with TSH (low T4 with low or inappropriately normal TSH), 9 a.m. cortisol with ACTH, testosterone or oestradiol with LH and FSH, IGF-1, and prolactin.
• Dynamic testing: short Synacthen test for the adrenal axis; insulin tolerance test (the gold standard for GH and ACTH reserve, but hazardous and contraindicated in ischaemic heart disease and epilepsy); glucagon stimulation as an alternative.
• MRI pituitary — in Sheehan's syndrome, the classic late finding is an empty sella.
• Electrolytes and glucose — hyponatraemia and hypoglycaemia; visual field testing where a mass is suspected.
• Water deprivation test if diabetes insipidus is suspected.

Management

Hormone replacement, in the correct order:

1. GLUCOCORTICOID FIRST — hydrocortisone, before any thyroid hormone.

2. Levothyroxine, titrated to free T4 (TSH is uninformative in secondary hypothyroidism).

3. Sex steroids — oestrogen with progestogen in women (until the usual age of menopause, for bone and cardiovascular protection), testosterone in men; gonadotrophin therapy where fertility is desired.

4. Growth hormone in children always, and in selected adults with documented deficiency.

5. Desmopressin for diabetes insipidus if present.

Patient education is identical to that in Addison's disease: sick-day rules with doubling of glucocorticoid during illness, a steroid card and emergency injection kit, and lifelong specialist follow-up. Treat the underlying cause where possible — surgery for a tumour, antitubercular therapy for tuberculous hypophysitis.