What is the most common cause of moon facies?

Most Common Cause of Moon Facies

Prolonged steroid usage (exogenous glucocorticoid administration) is the most common cause of moon facies. 1, 2

Understanding Moon Facies and Its Causes

Moon facies, characterized by a rounded, plethoric facial appearance, is a cardinal clinical manifestation of chronic hypercortisolism (Cushing's syndrome). When evaluating the potential causes of moon facies, we must consider the following etiologies in order of frequency:

1. Exogenous Steroid Use (Most Common)

• Prolonged administration of glucocorticoids (such as prednisone) is the most common cause of Cushing's syndrome and associated moon facies 1, 2
• Steroids can be administered through various routes:
  • Oral administration (most common)
  • Parenteral administration
  • Topical application (less common but still possible) 3, 4
  • Inhaled steroids (with high doses)

2. Pituitary Microadenoma (Cushing's Disease)

• Pituitary microadenomas causing excess ACTH production account for approximately 70% of endogenous Cushing's syndrome cases 1
• However, endogenous Cushing's syndrome itself is rare (prevalence <0.1% in general population) 1

3. Adrenal Causes

• Adrenal adenomas or carcinomas producing excess cortisol 5, 6
• These represent a smaller percentage of cases compared to exogenous steroid use

4. Other Rare Causes

• Ectopic ACTH production (e.g., from small cell lung cancer) 7
• Antibodies to adrenal cortex (Addison's disease typically causes hypocortisolism, not hypercortisolism)

Clinical Pearls and Pitfalls

• Key clinical finding: When moon facies is observed, always inquire about current or recent steroid use, including topical preparations 3, 4
• Common pitfall: Assuming moon facies in a patient on steroids is always iatrogenic - rarely, coincidental endogenous Cushing's syndrome can develop in patients already on steroids 6
• Diagnostic approach: For suspected Cushing's syndrome, screening tests include overnight 1-mg dexamethasone suppression test, 24-hour urinary free cortisol, and midnight salivary cortisol 1

Associated Features of Cushing's Syndrome

Moon facies is typically accompanied by other manifestations of Cushing's syndrome:

• Central obesity
• Buffalo hump
• Wide (1-cm) violaceous striae
• Proximal muscle weakness
• Hypertension (often resistant to treatment)
• Hyperglycemia/diabetes
• Psychiatric manifestations (depression, mood changes)
• Hirsutism
• Menstrual irregularities 7, 1

In summary, while there are multiple potential causes of moon facies, prolonged steroid usage (option A) represents the most common etiology in clinical practice, far exceeding the frequency of pituitary microadenomas, adrenal disorders, or autoimmune conditions.