Penyakit Addison

01Pathophysiology

Addison's disease results from the progressive destruction of the adrenal cortex, which must lose approximately 90% of its functional tissue before clinical insufficiency becomes apparent. The cortex is responsible for producing three classes of hormones: glucocorticoids (cortisol) from the zona fasciculata, mineralocorticoids (aldosterone) from the zona glomerulosa, and adrenal androgens (DHEA) from the zona reticularis.

When cortisol production falls, the hypothalamic-pituitary axis loses its negative feedback. The anterior pituitary responds by increasing secretion of ACTH, which is co-cleaved from the precursor molecule proopiomelanocortin (POMC). POMC also gives rise to melanocyte-stimulating hormone (MSH), and the excess MSH is what drives the characteristic hyperpigmentation. This is the single most important pathophysiologic link to understand for exam purposes: hyperpigmentation occurs because ACTH is elevated, and ACTH elevation only happens in primary adrenal failure, not secondary (pituitary) or tertiary (hypothalamic) insufficiency.

The loss of aldosterone is what distinguishes primary from secondary adrenal insufficiency at the metabolic level. Aldosterone normally acts on the distal tubule and collecting duct to reabsorb sodium and excrete potassium and hydrogen ions. Without aldosterone, the patient develops hyponatremia, hyperkalemia, and a non-anion gap metabolic acidosis (type IV renal tubular acidosis). The sodium wasting also causes volume depletion, contributing to the hypotension and salt craving. In secondary adrenal insufficiency, aldosterone is preserved because it is regulated primarily by the renin-angiotensin-aldosterone system (RAAS), not ACTH. This is why secondary insufficiency does not cause hyperkalemia.

Cortisol deficiency itself impairs vascular tone and the body's ability to mount a stress response. During physiologic stress (infection, surgery, trauma), the adrenal glands normally increase cortisol output several-fold. A patient with Addison's disease cannot do this, which is why they are at risk for adrenal crisis, a life-threatening emergency characterized by profound hypotension, shock, fever, and altered mental status.

02Classification and Clinical Manifestation

Clinical Manifestation

Adrenal crisis deserves special attention. It presents acutely with cardiovascular collapse, severe hypotension refractory to fluids and vasopressors, fever, abdominal pain mimicking an acute abdomen, altered consciousness, and severe electrolyte derangements. The most common precipitant is an intercurrent illness in a patient with undiagnosed Addison's disease, or a patient who fails to increase their steroid dose during physiologic stress.

03Diagnostic Workup

The cosyntropin stimulation test is the best initial diagnostic test and the most commonly tested step. Synthetic ACTH (cosyntropin, 250 mcg IV) is administered, and serum cortisol is measured at baseline, 30 minutes, and 60 minutes. In a healthy individual, cortisol should rise to at least 18-20 mcg/dL. In primary adrenal insufficiency, the adrenal glands are destroyed and cannot respond, so cortisol remains low regardless of ACTH stimulation.

Once the cosyntropin test confirms adrenal insufficiency, you need to determine whether it is primary or secondary. This is where the plasma ACTH level becomes critical. A high ACTH with a failed cosyntropin test confirms primary disease. A low ACTH with a failed cosyntropin test points to secondary insufficiency (pituitary problem), and you would then pursue pituitary MRI.

For identifying the underlying cause in primary disease, 21-hydroxylase antibodies help confirm autoimmune adrenalitis. If antibodies are negative, CT imaging of the adrenals is warranted to look for tuberculosis (bilateral adrenal calcification is classic), hemorrhage, or infiltrative disease.

An important lab pattern to recognize on the exam: hyponatremia + hyperkalemia + metabolic acidosis + eosinophilia in a patient with hypotension and hyperpigmentation. This combination should immediately trigger consideration of Addison's disease.

04Management and Treatment

Chronic management requires lifelong replacement of both cortisol and aldosterone. Hydrocortisone is preferred over other glucocorticoids because its short half-life allows dosing that mimics the normal diurnal cortisol curve. Prednisolone or dexamethasone can be used as alternatives, but dexamethasone has no mineralocorticoid activity and its long half-life makes physiologic dosing difficult.

Fludrocortisone replaces aldosterone. Its adequacy is monitored by checking blood pressure, serum potassium, and plasma renin activity. The goal is to normalize potassium and keep renin in the upper-normal range. Patients should be advised to maintain a liberal salt intake.

Adrenal crisis is a medical emergency. The single most important step is immediate IV hydrocortisone 100 mg before any diagnostic workup. Do not wait for lab confirmation. If the diagnosis is uncertain, dexamethasone 4 mg IV can be given instead because it does not interfere with the cosyntropin stimulation test (hydrocortisone cross-reacts with the cortisol assay, making subsequent testing uninterpretable). Aggressive volume resuscitation with isotonic saline is critical. Once the patient stabilizes, transition to oral replacement and taper to maintenance doses.

Stress dosing is a concept frequently tested. Patients must be educated to increase their glucocorticoid dose during febrile illness, trauma, or surgical procedures. Failure to stress-dose is the most common cause of adrenal crisis in a known Addison's patient. All patients should wear a medical alert bracelet and carry an emergency injectable hydrocortisone kit.

One key point: at high doses (> 50 mg/day), hydrocortisone provides adequate mineralocorticoid effect. Therefore, fludrocortisone is unnecessary during acute crisis management and can be added back once the patient is on maintenance doses.

05Differential Diagnosis and Distractors

The two most commonly confused entities on exams are primary vs. secondary adrenal insufficiency. The table below reinforces the distinction:

06Traps and High-Yield Pearls

The most common trap with Addison's disease questions is confusing primary with secondary adrenal insufficiency. Test-writers will present a patient on chronic prednisone who abruptly stops the medication and develops fatigue, hypotension, and hyponatremia. Students see "adrenal insufficiency" and jump to Addison's, but the absence of hyperkalemia and hyperpigmentation should redirect you to tertiary/secondary insufficiency from HPA axis suppression. Always check the potassium: if it is normal, this is not primary adrenal failure.

Another classic trap is the adrenal crisis scenario where the vignette buries the adrenal history and focuses on the acute presentation of shock, abdominal pain, and fever. Students anchor on sepsis, acute abdomen, or meningitis. The key trigger is unexplained hypotension refractory to fluids and vasopressors, especially with hyperkalemia and hyponatremia. In a patient with a history of autoimmune disease, tuberculosis, or steroid use, this should raise immediate concern.

The Waterhouse-Friderichsen syndrome vignette is high-yield: a child or young adult with meningococcal meningitis who develops purpura fulminans, DIC, and acute adrenal hemorrhage. This is acute primary adrenal insufficiency from bilateral adrenal hemorrhage, and the treatment is immediate IV hydrocortisone along with antibiotics and supportive care.

Remember that fludrocortisone is not needed in secondary insufficiency because aldosterone production is governed by the RAAS, which is independent of ACTH. This is tested frequently as an "unnecessary treatment" option.

Finally, the concept being tested is almost always one of three things: the ability to recognize the classic presentation (hyperpigmentation + hyperkalemia + hyponatremia + hypotension), the ability to distinguish primary from secondary causes using ACTH and potassium, or the knowledge that stress dosing is required and that failure to provide it is the most common precipitant of adrenal crisis.