AKT · Endocrine/Adrenal

Adrenal insufficiency (Addison's)

Cortisol ± aldosterone deficiency (primary adrenal vs secondary/pituitary)

Overview

Deficiency of adrenal cortical hormones. Primary (Addison's — autoimmune commonest in the UK, also TB worldwide, adrenal haemorrhage) loses BOTH cortisol and aldosterone → hyperpigmentation, hyponatraemia/hyperkalaemia. Secondary (pituitary ACTH deficiency, or abrupt steroid withdrawal) loses cortisol only — no hyperpigmentation, aldosterone preserved. The Addisonian crisis is the lethal emergency.

Recognise

Insidious fatigue, weight loss, anorexia, nausea, dizziness/postural hypotension, salt craving
PRIMARY: HYPERPIGMENTATION (palmar creases, buccal mucosa, scars — from high ACTH/MSH), hyponatraemia + HYPERkalaemia
SECONDARY: pale (no hyperpigmentation), no hyperkalaemia (aldosterone intact), other pituitary hormone deficits

Red flags

Addisonian CRISIS: hypotension/shock, vomiting, hyponatraemia, hypoglycaemia, often triggered by illness/surgery → emergency IV hydrocortisone + fluids (see acute care)
Don't start levothyroxine before steroid in coexisting hypothyroidism (precipitates crisis)

Differentials & how to tell them apart

Secondary adrenal insufficiencyno hyperpigmentation, normal potassium (aldosterone preserved), low ACTH — pituitary cause or steroid withdrawal

Sepsis/other shockthe crisis mimics shock — but responds to steroid; check the biochemistry

Haemochromatosis/other fatigue causessystemic illness; cortisol axis normal

Investigations

9 am cortisol (low) + ACTH (HIGH in primary, low in secondary); SHORT SYNACTHEN TEST (failure of cortisol to rise — the diagnostic test). U&Es (↓Na ↑K primary), glucose; adrenal autoantibodies (21-hydroxylase).

Management

Hydrocortisone + fludrocortisone (primary); sick-day rules + steroid card

1Specialist replacement: hydrocortisone (divided, diurnal) + fludrocortisone (primary). Educate on SICK-DAY RULES (double the glucocorticoid in illness, IM hydrocortisone if vomiting), steroid card and emergency kit.Gate: In a crisis, give IV/IM hydrocortisone and fluids IMMEDIATELY (don't wait for tests); never abruptly stop long-term steroids (causes secondary crisis); give glucocorticoid before thyroxine if both are deficient
2Increase steroid for surgery/illness; investigate the cause (autoimmune/TB/pituitary); screen for other autoimmune disease (polyglandular syndromes).

Hydrocortisone (glucocorticoid replacement) — divided doses mimicking the diurnal rhythm (highest on waking); double for illness ('sick-day rules')

Fludrocortisone (mineralocorticoid) — primary disease only — replaces aldosterone; do not restrict salt

Emergency IM hydrocortisone + steroid card/bracelet — for crisis prevention/self-management

Key points

Hyperpigmentation + ↓Na/↑K + postural drop = primary Addison's; the Synacthen test confirms it. The exam's killer is the crisis — treat first, test later — and the sick-day rules.

Monitor & prognosis

Symptoms, BP, U&Es; crisis preparedness.

Normal life on replacement; crisis is life-threatening.

Source: CKS Addison's; Society for Endocrinology