Situation: A 46-year-old man with primary adrenal insufficiency (Addison disease) is brought to the emergency department after 2 days of vomiting and diarrhea. He usually takes hydrocortisone 15 mg every morning and 5 mg every afternoon, and fludrocortisone 0.1 mg daily. He was treated for pulmonary tuberculosis 5 years ago. Which finding is expected in primary adrenal insufficiency and helps set it apart from the secondary (pituitary) form?

When the adrenal glands themselves fail, cortisol falls and the pituitary raises adrenocorticotropic hormone (ACTH); high ACTH stimulates skin pigment, darkening skin creases and gums. In secondary insufficiency ACTH is low, so hyperpigmentation does not occur. Weight loss, orthostatic dizziness, and hypoglycemia come from low cortisol and occur in both forms.

Core Pathophysiology
In primary adrenal insufficiency, the adrenal cortex itself is destroyed, so it cannot produce cortisol or aldosterone. The pituitary responds to the low cortisol by secreting more adrenocorticotropic hormone (ACTH). High circulating ACTH binds melanocortin receptors on melanocytes, increasing melanin production and causing hyperpigmentation of sun-exposed skin, palmar creases, buccal mucosa, and gums. In secondary adrenal insufficiency, the problem is in the pituitary or hypothalamus, so ACTH is low or absent; therefore, hyperpigmentation does not develop ^[1][2].

Why the Other Findings Do Not Differentiate
Weight loss with poor appetite, orthostatic dizziness, and fasting hypoglycemia all result from glucocorticoid deficiency itself. Because cortisol is low in both primary and secondary adrenal insufficiency, these manifestations appear in either form and cannot reliably separate the two ^[1][2]. Key point! Only the ACTH-dependent sign—hyperpigmentation—distinguishes primary from secondary disease.

Clinical Correlation With This Patient
This patient has a history of pulmonary tuberculosis treated 5 years ago. Tuberculosis can cause chronic granulomatous destruction of the adrenal glands, leading to primary adrenal insufficiency even years after successful antituberculous therapy ^[2]. The current presentation of vomiting, diarrhea, and likely dehydration places him at risk for adrenal crisis, which requires immediate glucocorticoid replacement ^[2]. His baseline regimen of hydrocortisone 15 mg in the morning and 5 mg in the afternoon, plus fludrocortisone 0.1 mg daily, reflects replacement of both glucocorticoid and mineralocorticoid—a pattern consistent with primary rather than secondary insufficiency.

Feature	Primary Adrenal Insufficiency	Secondary Adrenal Insufficiency
Site of defect	Adrenal cortex	Pituitary or hypothalamus
ACTH level	High	Low or normal
Hyperpigmentation	Present (skin, gums, creases)	Absent
Mineralocorticoid deficiency	Common (aldosterone low)	Rare (aldosterone usually preserved)
Weight loss, orthostatic dizziness, hypoglycemia	Present	Present

Why Hyperpigmentation Is the Best Discriminator
The melanocyte-stimulating activity of ACTH is the only clinical feature that directly reflects the level of pituitary drive, making skin and mucosal darkening a specific marker of primary adrenal failure. In a case report of primary adrenal insufficiency, tongue and gingival discoloration accompanied unintentional weight loss and skin hyperpigmentation, confirming that mucosal pigmentation is a recognizable sign of elevated ACTH ^[1]. A pediatric case with post-tuberculosis adrenal damage likewise presented with shock, hypoglycemia, and hyperpigmentation, underscoring that the pigment change is a core diagnostic clue ^[2].

Watch out! Do not rely on weight loss, postural dizziness, or hypoglycemia to localize the lesion. These reflect cortisol deficiency and are shared by both primary and secondary forms. Key point! When a patient with known adrenal insufficiency develops vomiting and diarrhea, assess for adrenal crisis and anticipate the need for stress-dose steroids, regardless of whether the underlying cause is primary or secondary ^[2].

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