Central Adrenal Insufficiency and Secondary Adrenal Insufficiency: Terminology
Yes, "central adrenal insufficiency" is another term for secondary adrenal insufficiency—they refer to the same condition where cortisol deficiency results from inadequate ACTH secretion by the pituitary gland or inadequate CRH secretion by the hypothalamus, rather than from primary adrenal gland failure. 1, 2
Terminology Clarification
The terms are used interchangeably in clinical practice and medical literature:
Secondary adrenal insufficiency specifically refers to deficient ACTH secretion by the pituitary gland, leading to reduced cortisol production despite intact adrenal glands 1
Central adrenal insufficiency (CAI) is the broader umbrella term that encompasses both pituitary (secondary) and hypothalamic causes of ACTH deficiency 2
Both conditions are characterized by low cortisol with low or inappropriately normal ACTH levels, distinguishing them from primary adrenal insufficiency where ACTH is elevated 1, 3, 2
The Three-Tier Classification System
Understanding the complete classification helps clarify why these terms overlap:
Primary adrenal insufficiency: The problem is in the adrenal gland itself (e.g., Addison's disease, congenital adrenal hyperplasia), resulting in deficiency of both cortisol and aldosterone 1, 3
Secondary adrenal insufficiency: The problem is in the pituitary gland with inadequate ACTH secretion 1, 4
Tertiary adrenal insufficiency: The problem is in the hypothalamus with inadequate CRH secretion, most commonly caused by chronic exogenous glucocorticoid therapy suppressing the hypothalamic-pituitary-adrenal axis 1
Important Clinical Distinction
The key practical difference is that patients with secondary/central adrenal insufficiency continue to secrete aldosterone in response to renin, so they do NOT require mineralocorticoid (fludrocortisone) replacement—only glucocorticoid replacement is needed. 1, 2 This contrasts with primary adrenal insufficiency where both glucocorticoid and mineralocorticoid replacement are required 5, 3.
Common Pitfall to Avoid
Don't assume that the absence of hyperkalemia rules out adrenal insufficiency—hyperkalemia is present in only about 50% of cases and is more characteristic of primary adrenal insufficiency where aldosterone deficiency occurs 1, 6. Patients with secondary/central adrenal insufficiency typically present with hyponatremia but maintain normal potassium levels because aldosterone secretion is preserved 1.