Hypothyroidism (Underactive Thyroid)

Hypothyroidism is a common endocrine disorder characterized by systemic thyroid hormone deficiency, leading to generalized slowing of basal metabolic processes. Primary hypothyroidism accounts for >99% of cases, arising from intrinsic thyroid gland failure.

• Chronic fatigue, lethargy, and somnolence (constant exhaustion)
• Cold intolerance (feeling cold when others are comfortable)
• Unexplained modest weight gain despite normal or reduced appetite
• Dry, coarse, scaly skin and brittle, thinning hair (loss of outer third of eyebrows - Queen Anne sign)
• Constipation due to decreased gastrointestinal motility
• Bradycardia (slow resting heart rate)
• Muscle weakness, proximal myopathy, and joint stiffness
• Menorrhagia (heavy, prolonged menstrual bleeding) or amenorrhea
• Depressed mood, impaired memory, and cognitive slowing ("brain fog")
• Puffy face, periorbital edema, and non-pitting edema (myxedema)

In iodine-sufficient regions, the leading etiology is Hashimoto Thyroiditis (Chronic Autoimmune Thyroiditis), characterized by autoimmune destruction of thyroid parenchyma mediated by anti-thyroperoxidase (anti-TPO) and anti-thyroglobulin (anti-Tg) antibodies. Worldwide, dietary iodine deficiency remains a common cause. Other causes: Post-radioactive iodine ablation, post-thyroidectomy, external radiation, and medications (Lithium, Amiodarone).

Laboratory serum testing is definitive:

• Primary Hypothyroidism: Elevated Serum TSH (>4.5-5.0 mIU/L) with Low Free T4 (Thyroxine)
• Subclinical Hypothyroidism: Elevated Serum TSH with Normal Free T4
• Autoimmune confirmation: Elevated Anti-Thyroid Peroxidase (Anti-TPO) Antibodies (>90% positive in Hashimoto disease)
• Lipid Profile: Significant elevations in serum Total and LDL cholesterol

Life-long oral hormone replacement therapy with synthetic Levothyroxine Sodium (L-T4):

• Dosing: Standard full replacement dose is approx. 1.6 mcg/kg/day (typically 75 to 125 mcg daily for adults). In elderly patients or those with coronary artery disease, start low: 12.5 to 25 mcg daily and titrate slowly.
• Administration Rules: Take first thing in the morning with a full glass of water, on an empty stomach, at least 30 to 60 minutes before breakfast, coffee, or other medications. Wait at least 4 hours before taking calcium, iron, or antacids.
• Monitoring: Recheck serum TSH 6 to 8 weeks after any dose adjustment until euthyroid, then annually.