Is hyperpigmentation a sign of Addison's disease or hypothyroidism?

Hyperpigmentation in Addison's Disease vs. Hypothyroidism

Hyperpigmentation is a classic sign of Addison's disease (primary adrenal insufficiency) but is not a characteristic feature of hypothyroidism. 1, 2

Addison's Disease and Hyperpigmentation

Mechanism and Presentation

• Hyperpigmentation in Addison's disease results from overproduction of adrenocorticotropic hormone (ACTH) by the pituitary gland as a compensatory mechanism for decreased cortisol production 1
• Characteristic features include:
  • Diffuse hyperpigmentation of the skin
  • Focal hyperpigmentation of scars, nails, and oral mucosa 2
  • Can be an early or isolated symptom, sometimes preceding other symptoms by years 3

Associated Symptoms

• Weakness and fatigue
• Anorexia and weight loss
• Electrolyte imbalances (decreased sodium, increased potassium)
• Hypotension
• "Flu-like" symptoms that may be subtle and repetitive 1, 4

Diagnostic Approach

• Morning serum cortisol measurement (8 AM) combined with ACTH levels is crucial for diagnosis 5
  • Morning cortisol <110 nmol/L (<4 μg/dL) suggests adrenal insufficiency
  • High ACTH with low cortisol indicates primary adrenal insufficiency (Addison's disease)
• Testing for 21-hydroxylase antibodies can confirm autoimmune etiology 3

Hypothyroidism and Skin Changes

Skin Manifestations in Hypothyroidism

• Hypothyroidism typically presents with:
  • Dry, cold, pale skin
  • Hair loss
  • Myxedema (non-pitting edema)
  • No characteristic hyperpigmentation (unlike Addison's disease)

Coexistence of Conditions

• Both conditions can coexist in autoimmune polyglandular syndrome type II (PAS II) 4, 6
• In such cases, hyperpigmentation is due to the Addison's disease component, not hypothyroidism

Clinical Pearls and Pitfalls

Important Considerations

• Hyperpigmentation may be the earliest or only sign of Addison's disease for years before other symptoms develop 3
• The presence of hyperpigmentation in a patient with hypothyroidism should raise suspicion for concurrent Addison's disease or PAS II 6
• Failure to recognize Addison's disease can lead to life-threatening adrenal crisis 2

Management Implications

• Patients with confirmed Addison's disease require lifelong glucocorticoid replacement (typically hydrocortisone 15-25 mg daily in divided doses) 5
• Mineralocorticoid replacement with fludrocortisone is also necessary for primary adrenal insufficiency 5, 4
• Patient education about stress dosing and adrenal crisis prevention is essential 5

In summary, when evaluating a patient with hyperpigmentation, Addison's disease should be strongly considered, while hypothyroidism alone does not cause this finding. The presence of hyperpigmentation in a patient with known hypothyroidism should prompt investigation for concurrent Addison's disease.