Adrenal Insufficiency Screening in Autoimmune Thyroid Disease

Rationale for Screening

Patients with autoimmune thyroid disease require continuous surveillance for other autoimmune disorders, particularly primary adrenal insufficiency (Addison's disease), as the presence of one autoimmune endocrine disorder substantially increases the risk of developing additional autoimmune endocrinopathies 1
Thyroid autoantibodies followed by development of hypothyroidism is frequently seen in patients with primary adrenal insufficiency, and the reverse association also occurs—patients with established autoimmune thyroid disease are at increased risk for developing adrenal insufficiency 1

Obtain paired early morning (8 AM) serum cortisol and plasma ACTH measurements as the first-line diagnostic test, and include a basic metabolic panel to assess for hyponatremia and hyperkalemia 2, 3
Basal cortisol <250 nmol/L (<9 μg/dL) with elevated ACTH in the presence of acute illness is diagnostic of primary adrenal insufficiency 2
If morning cortisol is indeterminate (neither clearly normal nor clearly low), proceed with ACTH stimulation testing 2

Administer 0.25 mg cosyntropin (tetracosactide) intramuscularly or intravenously, and measure serum cortisol at baseline and 30 minutes (and/or 60 minutes) post-administration 2
A peak cortisol <500 nmol/L (<18 μg/dL) is diagnostic of adrenal insufficiency, while >550 nmol/L is considered normal 2, 3

Measure 21-hydroxylase (anti-adrenal) autoantibodies to identify autoimmune etiology, which accounts for ~85% of primary adrenal insufficiency cases in Western populations 2, 3

If both adrenal insufficiency and hypothyroidism are present, corticosteroids must be started several days before initiating thyroid hormone replacement to prevent precipitating adrenal crisis 2
Starting thyroid hormone in a patient with undiagnosed adrenal insufficiency can unmask or worsen adrenal crisis by increasing metabolic demands 2
Regular monitoring of thyroid function every 12 months is important in patients with primary adrenal insufficiency, including serum TSH, FT4, and TPO antibodies 1

Unexplained collapse, hypotension, and gastrointestinal symptoms (vomiting or diarrhea) should immediately raise suspicion for adrenal insufficiency 2
Treatment of suspected acute adrenal insufficiency should NEVER be delayed for diagnostic procedures—give 100 mg IV hydrocortisone immediately plus 0.9% saline infusion if adrenal crisis is suspected 2