Causes of Secondary and Tertiary Adrenal Insufficiency
Secondary adrenal insufficiency results from inadequate ACTH secretion due to pituitary pathology, while tertiary adrenal insufficiency stems from hypothalamic dysfunction or—most commonly—suppression of the HPA axis by exogenous glucocorticoid therapy 1, 2, 3.
Secondary Adrenal Insufficiency (Pituitary-Level Causes)
Most Common Causes
- Pituitary tumors (adenomas, craniopharyngiomas) causing direct destruction or compression of corticotroph cells 3, 4
- Iatrogenic damage from pituitary surgery or radiation therapy for pituitary/hypothalamic tumors 3
- Pituitary apoplexy (sudden hemorrhage or infarction into pituitary tissue) 5
Less Common Causes
- Infiltrative diseases: lymphocytic hypophysitis, hemochromatosis, sarcoidosis, histiocytosis X 3
- Infectious processes: tuberculosis, fungal infections, abscess formation 3
- Vascular events: Sheehan syndrome (postpartum pituitary necrosis), pituitary infarction 3, 5
- Traumatic brain injury affecting the pituitary stalk or gland 6, 3
- Empty sella syndrome 3
- Genetic disorders affecting pituitary development or function 1, 3
- Immune checkpoint inhibitors causing hypophysitis (increasingly recognized) 5
Tertiary Adrenal Insufficiency (Hypothalamic-Level Causes)
Dominant Cause
Exogenous glucocorticoid therapy is by far the most common cause of tertiary adrenal insufficiency through negative feedback suppression of hypothalamic CRH secretion 7, 6, 5. This can occur with:
- Oral glucocorticoids at supraphysiologic doses (>5 mg prednisone equivalent daily) 7
- Inhaled glucocorticoids with significant systemic absorption 7
- Topical, intra-articular, or other formulations that achieve systemic levels 7
- Prolonged therapy (typically ≥3 months), though shorter courses can suppress the axis 7, 6
Other Hypothalamic Causes
- Hypothalamic tumors (craniopharyngiomas, gliomas, metastases) 3
- Hypothalamic radiation 3
- Infiltrative or inflammatory hypothalamic disease 3
- Chronic opioid use (emerging cause affecting hypothalamic function) 5
Critical Clinical Pitfalls
Glucocorticoid-Induced Adrenal Insufficiency
This deserves special emphasis as the most prevalent cause overall. The HPA axis typically recovers 6-12 months after glucocorticoid cessation, but timing is highly variable 6. High-risk periods include:
- Abrupt glucocorticoid withdrawal after long-term treatment 7
- Tapering below physiological doses (below 5 mg prednisone equivalent) 7
- Switching between inhaled glucocorticoid formulations with different systemic absorption profiles 7
- Initiation of CYP3A4 inducers (rifampicin, phenytoin, carbamazepine, phenobarbital) that accelerate glucocorticoid metabolism 7
Recognition Challenges
ACTH deficiency can be isolated or occur with other pituitary hormone deficiencies (panhypopituitarism) 3. When evaluating for secondary causes, always assess thyroid, gonadal, and growth hormone axes. The Danish study found increased incidence rate ratios after glucocorticoid discontinuation for hypotension (2.5), gastrointestinal symptoms (1.7), and hyponatremia (1.5) 7, highlighting that clinical manifestations may be subtle and delayed.
Unlike primary adrenal insufficiency, secondary and tertiary forms lack mineralocorticoid deficiency (no hyperkalemia or severe salt craving) since the renin-angiotensin-aldosterone system remains intact 2, 4. However, hyponatremia can still occur due to inappropriate ADH secretion from cortisol deficiency.
Mortality Risk
A UK study of 70,638 oral glucocorticoid users found sharply increased mortality in the first 2 months after cessation, rapidly decreasing after 3 months 7. While only 13 deaths were coded as adrenal insufficiency, the temporal relationship suggests undiagnosed adrenal crises 7. Supraphysiologic doses (>5 mg prednisone daily) carry an adjusted hazard ratio of 1.97 for all-cause mortality 7.