What are the causes of an elevated cortisol level?

Causes of Elevated Cortisol Levels

Elevated cortisol levels are caused by either exogenous corticosteroid administration (most common) or endogenous overproduction, which is divided into ACTH-dependent causes (pituitary adenomas causing Cushing's disease, ectopic ACTH-secreting tumors) and ACTH-independent causes (adrenal tumors or hyperplasia). 1

Primary Classification Framework

The causes of hypercortisolism follow a clear algorithmic structure:

1. Exogenous (Iatrogenic) Hypercortisolism

• Medically prescribed corticosteroids represent the most common cause of elevated cortisol levels overall 1
• This includes oral, inhaled, topical, or injectable glucocorticoid therapy
• Always verify medication history first before pursuing endogenous causes

2. Endogenous Hypercortisolism

ACTH-Dependent Causes (excess ACTH drives cortisol production):

• Pituitary corticotroph adenomas (Cushing's disease): The most common cause of endogenous Cushing's syndrome 2

  • Typically microadenomas secreting ACTH
  • Accounts for majority of endogenous cases

• Ectopic ACTH secretion: 3

  • Lung carcinoids or carcinomas
  • Pancreatic tumors
  • Pheochromocytomas
  • Other neuroendocrine tumors

ACTH-Independent Causes (autonomous adrenal cortisol production):

• Adrenal adenomas: Benign functioning tumors
• Adrenal carcinomas: Malignant cortisol-secreting tumors
• Bilateral adrenal hyperplasia: Non-tumorous adrenocortical hyperfunction 3
• Mild autonomous cortisol secretion (MACS): An increasingly recognized entity that lacks overt Cushingoid features but still causes significant cardiometabolic complications 4

3. Pseudo-Cushing States (Physiological Hypercortisolism)

These conditions activate the HPA axis without true pathological Cushing's syndrome but can produce elevated cortisol and mimic biochemical findings: 1

• Psychiatric disorders: Depression, anxiety disorder, obsessive-compulsive disorder
• Poorly controlled diabetes mellitus
• Alcoholism
• Severe obesity: Can raise urinary free cortisol despite normal or slightly reduced circulating cortisol
• Chronic stress states

Higher brain centers stimulate CRH release in these conditions, activating the entire HPA axis, though negative feedback mechanisms partially restrain the response 1

Clinical Context and Prevalence

The incidence of endogenous Cushing's syndrome is approximately 2-3 cases per million inhabitants per year in European populations 1. However, recent evidence suggests hypercortisolism is substantially underdiagnosed, particularly in specific populations:

• 24% prevalence in patients with difficult-to-control type 2 diabetes 5
• 27-37% prevalence in patients with resistant hypertension (requiring ≥3 antihypertensive medications) 5, 6

Important Clinical Pitfalls

The most critical error is failing to consider Cushing's syndrome as a secondary cause of common conditions. 1 Many patients present with non-specific features common in the general population (obesity, depression, diabetes, hypertension, menstrual irregularity) rather than classic Cushingoid features, leading to diagnostic delays.

A defective interpretation of cortisol results is another major pitfall: 7 Cortisol measured at standard times (0800h or 1700h) may appear normal despite pathological swings to immunosuppressive levels during the 24-hour circadian rhythm. This is why late-night salivary cortisol testing is recommended to assess loss of normal circadian rhythm 2.

MACS represents a particularly underrecognized entity 4 because patients lack obvious cushingoid features despite having substantial cardiometabolic and skeletal risk, making it easy to miss without appropriate screening in high-risk populations.

When to Suspect Elevated Cortisol

Consider hypercortisolism when patients present with:

• Discriminatory features (higher specificity): Reddish-purple striae >1cm wide, facial plethora, proximal muscle weakness, easy bruising without trauma, unexplained osteoporosis 1
• Common features with additional suspicious findings: Obesity, hypertension, diabetes, or depression combined with any discriminatory features
• Resistant hypertension requiring ≥3 medications 5, 6
• Difficult-to-control diabetes 5
• Children with weight gain and decreasing growth velocity 1