Is an abdominal computed tomography (CT) scan with contrast indicated for a patient with a new diagnosis of hypothyroidism to evaluate the adrenal glands for potential adrenal insufficiency or other adrenal pathologies?

Abdominal CT is NOT Indicated for Routine Evaluation of Adrenal Glands in New Hypothyroidism

An abdominal CT scan is not recommended for evaluating adrenal glands in patients with newly diagnosed hypothyroidism unless there are specific clinical features suggesting adrenal insufficiency or other adrenal pathology.

Clinical Context and Reasoning

When Hypothyroidism Alone Does Not Warrant Adrenal Imaging

• Primary hypothyroidism by itself is not an indication for adrenal imaging 1
• The elevated TSH levels (typically 4-10 IU/L) sometimes seen in primary adrenal insufficiency (PAI) occur due to lack of cortisol's inhibitory effect on TSH production, not the reverse 1
• If hypothyroidism is the primary diagnosis without signs of adrenal dysfunction, adrenal imaging serves no clinical purpose

When to Consider Adrenal Evaluation

The diagnosis of primary adrenal insufficiency should be considered and investigated when patients present with specific clinical and biochemical features 1:

• Unexplained collapse, hypotension, or hemodynamic instability 1
• Hyperpigmentation (a hallmark of primary adrenal insufficiency) 1
• Electrolyte abnormalities: hyponatremia, hyperkalemia, or acidosis 1
• Hypoglycemia 1
• Persistent vomiting or diarrhea 1

Appropriate Diagnostic Pathway for Suspected Adrenal Insufficiency

If clinical suspicion for adrenal insufficiency exists, the correct diagnostic approach is biochemical testing first, not imaging 1:

1. Paired measurement of early morning (8 AM) serum cortisol and plasma ACTH is the diagnostic test of choice 1
2. A serum cortisol <250 nmol/L with elevated ACTH in acute illness is diagnostic of primary adrenal insufficiency 1
3. Serum cortisol <400 nmol/L with elevated ACTH raises strong suspicion 1
4. In equivocal cases, a cosyntropin (synacthen) stimulation test with peak serum cortisol <500 nmol/L confirms PAI 1

Role of CT in Confirmed Adrenal Insufficiency

CT imaging of the adrenal glands is only indicated AFTER biochemical confirmation of primary adrenal insufficiency to determine etiology 1:

• First, measure serum 21-hydroxylase (anti-adrenal) autoantibodies to assess for autoimmune etiology 1
• If antibodies are negative, then CT imaging is recommended to evaluate for structural causes such as hemorrhage, infection (tuberculosis), infiltrative disease, or metastases 1
• In male patients with negative antibodies, also assay very long-chain fatty acids to screen for adrenoleukodystrophy 1, 2

Special Consideration: Immune Checkpoint Inhibitor Therapy

If the patient is receiving immune checkpoint inhibitor therapy (anti-CTLA-4 or anti-PD-1/PD-L1 agents), a different approach applies 1:

• Routine monitoring with early morning ACTH and cortisol should be considered (monthly for 6 months, then every 3 months) 1
• Hypothyroidism in this context may signal hypophysitis (central hypothyroidism with low/normal TSH and low free T4) 1
• MRI of the sella with pituitary cuts is indicated for suspected hypophysitis, not abdominal CT 1

Common Pitfalls to Avoid

• Do not order abdominal CT based solely on hypothyroidism diagnosis - this represents inappropriate use of imaging resources 1
• Do not skip biochemical testing - imaging cannot diagnose adrenal insufficiency; only biochemical testing can 1
• Do not delay treatment for diagnostic imaging if acute adrenal crisis is suspected clinically 1
• Remember that incidental adrenal masses are common (up to 5% of abdominal CTs) and most are benign adenomas, which could lead to unnecessary follow-up and anxiety if CT is performed without indication 1, 3, 4