1Clinical Presentation: Symptoms & Signs
Diagnostic Symptoms
- Fatigue, lethargy, weight gain despite reduced appetite
- Cold intolerance and dry, scaly skin
- Diffuse hair thinning and loss of outer third of eyebrows
- Chronic constipation and hoarseness of voice
- Proximal muscle weakness, cramps, and myalgias
- Menstrual disturbances: menorrhagia progressing to oligomenorrhea
- Neurocognitive slowing, poor concentration, "brain fog"
- Carpal tunnel syndrome and peripheral paresthesias
Physical Signs
- Non-pitting myxoedema (puffy facies, hands, and feet)
- Periorbital oedema and pallor
- Sinus bradycardia (pulse <60 bpm)
- Delayed relaxation phase of ankle tendon reflexes (Woltman sign)
- Enlarged thyroid (goitre) or impalpable atrophic gland
- Cool, dry, coarse, and yellowish skin (carotenemia)
- Slowed speech and psychomotor retardation
- Serous cavity effusions (pericardial, pleural) in severe states
2Investigations & Laboratory Interpretation
| Category | Diagnostic Workup | Biochemical Interpretation |
|---|---|---|
| Primary Hypothyroidism | Serum TSH · Free T4 (FT4) · Anti-TPO antibodies | Overt: Elevated TSH (>10 mIU/L) + Subnormal FT4 Subclinical: Elevated TSH (4.5–10 mIU/L) + Normal FT4 |
| Congenital Hypothyroidism | Neonatal dried blood spot TSH · FT4 · Thyroid USG / Tc-99m scan | Screening: TSH > 30 mIU/L (cord/heel prick) Confirmatory: TSH > 9 mIU/L + FT4 < 0.6 ng/dL (start Rx immediately) |
| Central (Pituitary/Secondary) | FT4 · TSH · Anterior pituitary profile (Cortisol, ACTH, Prolactin) · Sellar MRI | Subnormal or inappropriately normal TSH with low FT4. |
3Levothyroxine Dosing — ICMR STW Guidelines
| Clinical Subtype | Initial Replacement Dose | Administration & Precaution Notes |
|---|---|---|
| Adult Primary (Overt) | 1.6 – 1.8 mcg/kg/day | Take on an empty stomach with plain water 30–60 minutes before breakfast. Elderly or known CAD: start at 12.5–25 mcg/day; uptitrate by 12.5–25 mcg every 3–4 weeks. |
| Congenital Hypothyroidism | 10 – 15 mcg/kg/day | Single daily dose crushed in breast milk. Titrate aggressively based on FT4 and TSH to safeguard neurodevelopment. |
| Central Hypothyroidism | 1.3 mcg/kg/day | CRITICAL: Exclude or treat coexisting adrenal insufficiency with hydrocortisone BEFORE initiating levothyroxine to prevent an adrenal crisis. |
When to Treat Subclinical Hypothyroidism (TSH 4.5–10 mIU/L): ICMR STW advises initiating therapy if accompanied by: high anti-TPO antibody titres, symptomatic goitre, female infertility or pregnancy plans, severe dyslipidaemia, established ASCVD, depression, or refractory anaemia.
4Age-Adjusted Target TSH Ranges
Young Adults
1.0 – 2.5 mIU/L
Middle-Aged
1.5 – 3.0 mIU/L
Elderly (<60 yr)
> 4.5 mIU/L
Elderly (60–70 yr)
> 6.0 mIU/L
Elderly (70–80 yr)
> 7.0 – 8.0 mIU/L
Congenital Target
0.5 – 2.0 mIU/L
5Follow-Up & Monitoring Interval
Primary / Central Hypothyroidism
- Recheck TSH every 6–8 weeks following any dosage adjustment.
- Once stable euthyroid dose is achieved, monitor TSH every 6–12 months.
- In central hypothyroidism: monitor Free T4/Total T4 (TSH is unreliable).
Congenital Hypothyroidism
- Initial review at 2 weeks, then at 4 weeks post-initiation.
- Every 1–2 months throughout the first 6 months of life.
- Every 3–4 months from 6 months to 3 years of age.
- Every 6–12 months thereafter until linear growth and puberty are complete.
6Frequently Asked Questions
What are the symptoms of hypothyroidism?+
Classic symptoms include fatigue, cold intolerance, constipation, weight gain, dry skin, diffuse hair loss, bradycardia, myalgias, depression, and facial puffiness. In severe disease, myxoedema coma can develop.
What is the most common cause of hypothyroidism in India?+
Hashimoto thyroiditis (chronic autoimmune thyroiditis with positive anti-TPO) is the primary cause in iodine-replete urban centers. Endemic goitre and iodine deficiency still occur in remote sub-Himalayan belts. Post-surgical and post-radioiodine therapy represent major iatrogenic etiologies.
How should levothyroxine be ingested correctly?+
Take with a full glass of plain water upon waking, 30 to 60 minutes before tea, coffee, breakfast, or other medications. Calcium, iron, antacids, and proton pump inhibitors (PPIs) severely bind levothyroxine and must be spaced at least 4 hours apart.
What constitutes myxoedema coma and how is it managed?+
Myxoedema coma is an endocrine emergency characterized by severe hypothermia, bradycardia, hypoventilation, hyponatraemia, and altered mental status. Precipitants include sepsis, cold exposure, or sedatives. Management requires ICU admission, IV hydrocortisone (100 mg IV q8h prior to thyroid replacement to avoid precipitating adrenal crisis), followed by IV levothyroxine and passive warming.
Clinical Disclaimer: The Billewicz Score serves as an adjunct diagnostic scoring tool. Biochemical confirmation via serum TSH and Free T4 remains the gold standard. Verify dosage requirements against patient weight, cardiac history, and age-adjusted TSH targets.