A 41-year-old woman is brought to the emergency department by her husband due to severe di… — USMLE Step 2 CK

A $41$ -year-old woman is brought to the emergency department by her husband due to severe dizziness, intractable vomiting, and confusion that started earlier today. Two weeks ago, the patient was diagnosed with primary hypothyroidism after presenting with profound fatigue, muscle aches, and unintended weight loss. At that time, her thyroid-stimulating hormone level was $18.5$ mU/L (Normal: $0.4-4.0$ mU/L) and free thyroxine was $0.5$ ng/dL (Normal: $0.8-1.8$ ng/dL). She was prescribed levothyroxine $100$ $\mu$ g daily, which she has been taking as directed. The patient's medical history is significant for vitiligo. She does not take any other medications.

On physical examination, temperature is $37.6^\circ$ C ( $99.7^\circ$ F), blood pressure is $78/48$ mmHg, heart rate is $118$ /min, and respiratory rate is $20$ /min. The patient appears lethargic. Skin examination reveals depigmented patches on her hands and face, as well as noticeable hyperpigmentation of the palmar creases and oral mucosa.

Laboratory studies show:

Laboratory Test	Result	Reference Range
Serum sodium	$127$ mEq/L	$136-145$ mEq/L
Serum potassium	$5.8$ mEq/L	$3.5-5.0$ mEq/L
Serum chloride	$95$ mEq/L	$98-106$ mEq/L
Serum bicarbonate	$18$ mEq/L	$22-28$ mEq/L
Serum glucose	$54$ mg/dL	$70-99$ mg/dL (fasting)

Which of the following best explains the mechanism of this patient's acute clinical deterioration?

Increased hepatic clearance of cortisol induced by thyroid hormone replacementAnswer
B
Decreased adrenocorticotropic hormone secretion due to thyroxine negative feedback
C
Autoimmune destruction of the adrenal medulla leading to catecholamine deficiency
D
Excessive levothyroxine dosing leading to high-output heart failure
E
Shift of intracellular potassium to the extracellular space due to insulin deficiency

Answer

The acute deterioration is caused by increased hepatic clearance of cortisol induced by thyroid hormone replacement.

This patient's presentation of severe hypotension, hyponatremia, hyperkalemia, hypoglycemia, and characteristic hyperpigmentation (palmar creases, oral mucosa) is highly diagnostic of primary adrenal insufficiency (Addison disease) presenting as an acute adrenal crisis. The patient has a history of autoimmune diseases (vitiligo, Hashimoto thyroiditis), making Autoimmune Polyglandular Syndrome type 2 the most likely etiology. Before starting thyroid hormone replacement in any patient with suspected or confirmed multiple autoimmune endocrinopathies, it is critical to rule out adrenal insufficiency. Levothyroxine increases the basal metabolic rate and upregulates hepatic enzymes responsible for the metabolic clearance of circulating glucocorticoids. In a patient with diminished adrenal reserve who is barely maintaining homeostasis, this sudden increased demand and clearance of cortisol rapidly depletes cortisol levels, precipitating an acute adrenal crisis.

Step-by-Step Solution

Identify the primary clinical syndrome based on the physical examination and laboratory findings.

The patient has hypotension, hypoglycemia, hyponatremia, hyperkalemia, non-anion gap metabolic acidosis, and mucosal/palmar hyperpigmentation.

These findings are classic for primary adrenal insufficiency (Addison disease), which is currently manifesting as an acute adrenal crisis.

Establish the relationship between the patient's existing conditions and the new diagnosis.

The presence of primary hypothyroidism, vitiligo, and primary adrenal insufficiency suggests Autoimmune Polyglandular Syndrome type 2 (Schmidt syndrome).

Autoimmune conditions frequently cluster in patients with specific HLA haplotypes.

Determine the pathophysiological trigger for the acute adrenal crisis in this specific clinical context.

The crisis occurred two weeks after initiating levothyroxine therapy for primary hypothyroidism.

Thyroid hormone increases basal metabolic rate and hepatic metabolism. In a patient with unrecognized, untreated adrenal insufficiency, administering levothyroxine accelerates the clearance of whatever minimal cortisol the patient is still producing, thereby unmasking the deficiency and precipitating a life-threatening adrenal crisis.

Key Concept

Initiating levothyroxine in a patient with undiagnosed primary adrenal insufficiency increases hepatic cortisol clearance and can precipitate an acute, life-threatening adrenal crisis.

Question

Answer

Step-by-Step Solution

Key Concept

Common Mistakes

Topics

More questions from this topic