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Difficulty: MediumEndocrinology and Metabolism

Over the past 33 months, a 3434-year-old female patient has experienced progressive fatigue, unexplained weight loss of 4 kg4 \text{ kg} (8.8 lb8.8 \text{ lb}), and recurrent nausea. She specifically notes a new, intense craving for salty snacks. Her past medical history includes Hashimoto thyroiditis, currently managed with daily levothyroxine. During the physical examination, her blood pressure is 102/65 mm Hg102/65 \text{ mm Hg} while lying down, which drops to 86/55 mm Hg86/55 \text{ mm Hg} when she stands. The physician notes distinct hyperpigmentation on the oral mucosa and along the palmar creases. Laboratory evaluation reveals:

ParameterResultReference Range
Sodium130 mEq/L130 \text{ mEq/L}136−145 mEq/L136-145 \text{ mEq/L}
Potassium5.3 mEq/L5.3 \text{ mEq/L}3.5−5.0 mEq/L3.5-5.0 \text{ mEq/L}
Glucose (fasting)72 mg/dL72 \text{ mg/dL}70−99 mg/dL70-99 \text{ mg/dL}

Which of the following laboratory patterns regarding adrenocorticotropic hormone (ACTH), aldosterone, and plasma renin activity is most expected in this patient?

  1. Elevated ACTH, decreased aldosterone, elevated plasma renin activityAnswer
  2. B
    Decreased ACTH, normal aldosterone, normal plasma renin activity
  3. C
    Decreased ACTH, decreased aldosterone, elevated plasma renin activity
  4. D
    Elevated ACTH, increased aldosterone, decreased plasma renin activity
  5. E
    Normal ACTH, decreased aldosterone, decreased plasma renin activity

Answer

The expected pattern is elevated ACTH, decreased aldosterone, and elevated plasma renin activity.
The correct answer describes the exact laboratory derangement found in primary adrenal insufficiency. Autoimmune adrenalitis (often associated with Hashimoto thyroiditis in polyglandular autoimmune syndromes) destroys all three zones of the adrenal cortex. The loss of cortisol eliminates negative feedback on the hypothalamus and pituitary, leading to a marked elevation of ACTH (along with MSH, causing hyperpigmentation). The concurrent destruction of the zona glomerulosa halts aldosterone production, leading to renal sodium wasting, potassium retention, and volume depletion. This hypovolemia robustly stimulates the kidneys to release renin, resulting in elevated plasma renin activity.

Step-by-Step Solution

1
Identify the clinical syndrome based on the patient's symptoms and laboratory findings.
The combination of fatigue, weight loss, salt craving, orthostatic hypotension, hyperpigmentation, hyponatremia, and hyperkalemia points to primary adrenal insufficiency (Addison disease).
These findings indicate deficiencies in both glucocorticoids (causing fatigue and weight loss) and mineralocorticoids (causing salt wasting, hypotension, and hyperkalemia).
2
Determine the expected level of ACTH.
ACTH will be elevated.
In primary adrenal insufficiency, the adrenal cortex is destroyed and cannot produce cortisol. The lack of cortisol removes negative feedback on the anterior pituitary, leading to increased POMC transcription. POMC is cleaved into ACTH and melanocyte-stimulating hormone (MSH), explaining the elevated ACTH and mucosal hyperpigmentation.
3
Determine the expected levels of aldosterone and plasma renin activity.
Aldosterone will be decreased, and plasma renin activity will be elevated.
Cortical destruction directly halts aldosterone synthesis. The resulting sodium loss and intravascular volume depletion stimulate the juxtaglomerular apparatus in the kidneys to secrete large amounts of renin in a compensatory, though futile, attempt to stimulate aldosterone production.

Key Concept

Diagnosis and laboratory evaluation of primary adrenal insufficiency (Addison disease).
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Topics

Endocrinology and Metabolism

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