Addison's Disease
Primary adrenal insufficiency — failure of the adrenal glands to produce adequate cortisol and aldosterone. Cosyntropin (synthetic ACTH fragment) is the standard diagnostic test: it is injected and cortisol response is measured to assess adrenal function.
Technical Context
Primary adrenal insufficiency: autoimmune adrenalitis accounts for approximately 80% in developed countries (adrenal cortex antibodies against 21-hydroxylase). Other causes: infections (tuberculosis — still common in developing countries, HIV-associated), bilateral adrenalectomy, haemorrhagic infarction (Waterhouse-Friderichsen syndrome), metastatic cancer, and genetic (congenital adrenal hyperplasia). Clinical features: fatigue, weight loss, hyperpigmentation (ACTH excess → MC1R stimulation on melanocytes), hypotension (aldosterone deficiency), hyponatraemia, hyperkalaemia, and adrenal crisis (life-threatening hypotension/shock precipitated by stress/infection). Diagnosis: morning cortisol <3 μg/dL is diagnostic; cosyntropin stimulation test (250μg IM/IV → cortisol measured at 30/60 min; peak <18-20 μg/dL confirms adrenal insufficiency). Cosyntropin (synthetic ACTH 1-24) is the standard diagnostic peptide drug for adrenal function assessment. Treatment: lifelong glucocorticoid replacement (hydrocortisone) ± mineralocorticoid (fludrocortisone).