VHOSPITAL.CLINIC · Differential Diagnosis
Addison's Disease vs Hypothyroidism
Clinical comparison — shared symptoms, key differences, distinguishing diagnostic tests, treatment pathways, and when to seek urgent evaluation.
Condition Overview
Condition A
Addison's Disease
Addison's disease is primary adrenal insufficiency causing insufficient production of cortisol and aldosterone. Symptoms include fatigue, weight loss, hyperpigmentation, low blood pressure, and salt craving; lifelong hormone replacement is required.
Condition B
Hypothyroidism
Hypothyroidism occurs when the thyroid gland doesn't produce enough thyroid hormone. This slows metabolism and causes fatigue, weight gain, cold intolerance, constipation, and depression. Hashimoto's thyroiditis is the most common cause.
Shared Symptoms — Why They're Confused
Both conditions present with 1 overlapping symptom, making clinical differentiation essential.
Key Clinical Differences
Addison's Disease
- Fatigue, weight loss, hyperpigmentation, postural hypotension
- Salt craving, nausea, vomiting, diarrhoea
- Hyponatraemia + hyperkalaemia
- Adrenal crisis: severe hypotension, vomiting, abdominal pain
Hypothyroidism
- Fatigue, weight gain, cold intolerance, constipation
- Dry skin, hair loss, myxoedema
- Bradycardia, delayed reflexes
- Hyponatraemia (SIADH); no hyperkalaemia
Distinguishing Diagnostic Tests
| Test | Addison's Disease | Hypothyroidism |
|---|---|---|
| Short Synacthen test (SST) | Cortisol fails to rise adequately (peak <500 nmol/L) — adrenal insufficiency | Normal cortisol response — no adrenal insufficiency |
| TSH + Free T4 | Normal thyroid function — but secondary AI can suppress TSH | Elevated TSH, low Free T4 — primary hypothyroidism |
| Electrolytes | Hyponatraemia + hyperkalaemia — classic for Addison's | Hyponatraemia only (SIADH); potassium normal |
Treatment Approaches
Addison's Disease
- •Hydrocortisone + fludrocortisone replacement (lifelong)
- •Sick-day rules: double dose during illness
- •Emergency hydrocortisone injection kit
Hypothyroidism
- •Levothyroxine replacement
- •Annual TFT monitoring
- •Caution: replace thyroid before adrenal in combined failure (Schmidt syndrome)
When Doctors Consider Each Diagnosis
🔵 Consider Addison's Disease when:
- →Hyperpigmentation, salt craving, hyperkalaemia, postural hypotension, abnormal SST
🟢 Consider Hypothyroidism when:
- →Weight gain, cold intolerance, constipation, bradycardia, elevated TSH
Explore Each Condition in Detail
Related Clinical Pages
Addison's Disease
Medical References
Content on this page is informed by evidence-based clinical sources including:
- World Health Organization (WHO)Global health guidance and disease classification
- National Health Service (NHS)UK clinical guidelines and patient information
- National Institute for Health and Care Excellence (NICE)Evidence-based clinical practice guidelines
- Centers for Disease Control and Prevention (CDC)US public health data and clinical recommendations
- PubMed – NCBIPeer-reviewed biomedical literature and clinical studies
- Cochrane LibrarySystematic reviews and meta-analyses in evidence-based medicine
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