Clues Pointing TO This Diagnosis

Months of progressive fatigue — fatigue is the most common symptom of primary adrenal insufficiency, occurring in up to 95% of patients
Unintentional weight loss of ten pounds — anorexia and weight loss occur in roughly 67%–73% of patients with primary adrenal insufficiency
Morning nausea — nausea, vomiting, and abdominal discomfort occur in about 62% of patients
Salt craving — salt craving (roughly 12%–19%) reflects the mineralocorticoid (aldosterone) deficiency specific to primary adrenal insufficiency
Hyperpigmentation, including palmar creases — seen in about 74% of primary cases; high corticotropin (ACTH) drives melanocyte stimulation, a finding specific to primary disease
Orthostatic hypotension with dizziness on standing — postural hypotension occurs in about 68% and reflects volume/mineralocorticoid deficiency
Syncope at the faculty meeting — hypotension from combined cortisol and aldosterone deficiency can progress to collapse
Flat (low) morning cortisol — a morning cortisol <5 µg/dL supports adrenal insufficiency
Elevated ACTH — high corticotropin with low cortisol confirms the defect is at the adrenal gland (primary)
Autoimmune etiology in a middle-aged adult — autoimmune destruction (Addison's disease) is the most common cause of primary adrenal insufficiency in developed countries

Why It's NOT the Similar Diseases

NOT secondary (pituitary) adrenal insufficiency — Winston Jr has hyperpigmentation, salt craving, and elevated ACTH; secondary disease has low/normal ACTH, no hyperpigmentation, and preserved aldosterone (no salt craving)
NOT glucocorticoid-induced adrenal insufficiency — there is no history of taking supraphysiologic glucocorticoids that were tapered; his ACTH is high rather than suppressed
NOT primary hypothyroidism — fatigue and weight change overlap, but hypothyroidism causes weight gain, cold intolerance, and does not produce hyperpigmentation, salt craving, or orthostatic hypotension
NOT depression/chronic fatigue — mood or fatigue syndromes do not explain hyperpigmentation, orthostatic hypotension, hyponatremia/hyperkalemia, or low cortisol with high ACTH
NOT gastrointestinal malignancy — weight loss and nausea could suggest cancer, but the endocrine signature (hyperpigmentation, salt craving, low cortisol, high ACTH) identifies adrenal insufficiency

Differential Diagnosis List

Secondary adrenal insufficiency — ruled out by elevated ACTH, hyperpigmentation, and salt craving indicating a primary adrenal defect
Glucocorticoid-induced adrenal insufficiency — ruled out by absence of exogenous glucocorticoid use and by high (not suppressed) ACTH
Primary hypothyroidism — ruled out by weight loss rather than gain and by hyperpigmentation and orthostasis not explained by thyroid disease
Major depression/chronic fatigue syndrome — ruled out by objective findings of hyperpigmentation, hypotension, and abnormal cortisol/ACTH
Gastrointestinal malignancy — ruled out by the characteristic adrenal endocrine profile confirming cortisol deficiency

Key Distinguishing Test

Early-morning (~8 am) serum cortisol together with plasma ACTH (corticotropin) is the initial confirmatory testing: a low morning cortisol (<5 µg/dL) with a high ACTH confirms primary adrenal insufficiency, and a low DHEAS supports the diagnosis.
When the morning cortisol is intermediate (5–10 µg/dL), a cosyntropin (ACTH) stimulation test is used—cortisol is measured before and 60 minutes after 250 µg cosyntropin, and a peak <18 µg/dL confirms adrenal insufficiency.
In primary disease, plasma renin is high and aldosterone is low, and 21-hydroxylase antibodies confirm autoimmune (Addison's) etiology.

Board Note

Primary adrenal insufficiency (Addison's disease) involves loss of both cortisol and aldosterone; the combination of hyperpigmentation, salt craving, orthostatic hypotension, hyponatremia, and hyperkalemia is the classic picture, and autoimmune destruction is the most common cause in developed countries
Diagnosis: low morning cortisol + high ACTH confirms primary disease; use the cosyntropin stimulation test for equivocal cortisol values; check 21-hydroxylase antibodies for etiology
Treatment requires both a glucocorticoid (hydrocortisone 15–25 mg/day in divided doses, or prednisone) and a mineralocorticoid (fludrocortisone ~0.1 mg daily), the latter being unique to primary disease
Every patient needs sick-day/stress-dosing education, a medical alert bracelet, and injectable hydrocortisone (100 mg IM) for emergencies; stress dosing roughly doubles/triples glucocorticoids during febrile illness, and surgery or severe illness requires parenteral dosing
Adrenal crisis is the life-threatening complication—hypotension/shock, hyponatremia, and altered mental status; treat immediately with IV/IM hydrocortisone 100 mg and rapid IV normal saline without waiting for test results, and treat the precipitant
Associations to remember: autoimmune adrenalitis frequently coexists with other autoimmune conditions (e.g., autoimmune thyroid disease, type 1 diabetes); monitor yearly, and refer to endocrinology for diagnosis confirmation and management

“Winston Jr’s Story”