Hypothyroidism: Symptoms, TSH Diagnosis and Treatment

Unexplained fatigue, weight gain without any change in diet, feeling cold even in summer, depression that has no obvious trigger — these symptoms are written off as "burnout" for years. Yet in one in ten women over 40 they have a specific laboratory cause: hypothyroidism. Let's look at how the thyroid works, why its failure stays hidden for so long, and what tests reveal it.

What Is Hypothyroidism and Why It Goes Unnoticed

Hypothyroidism means the thyroid gland produces less T4 and T3 than the body needs. Thyroid hormones set the metabolic pace for every cell: heart rate, how fast food is converted to energy, body temperature, thinking speed.

When hormone levels drop, everything slows — gradually and uniformly. This gradual onset is precisely what makes hypothyroidism so easy to miss: people adapt to their new lower energy baseline.

Causes of Hypothyroidism

Hashimoto's thyroiditis — the leading cause in developed countries. The immune system mistakenly attacks thyroid tissue, progressively destroying it.

Treatment of hyperthyroidism — radioiodine therapy and thyroid surgery frequently result in hypothyroidism requiring lifelong replacement therapy.

Iodine deficiency — relevant in endemic goiter regions.

Congenital hypothyroidism — detected by newborn screening in the first days of life.

Central hypothyroidism — rare: the thyroid is healthy but the pituitary produces insufficient TSH to stimulate it.

Symptoms of Hypothyroidism

Metabolic: weight gain without dietary changes; cold intolerance; constipation.

Neurological and psychological: chronic fatigue; slowed thinking, memory impairment; depression, apathy.

Cardiovascular: bradycardia (heart rate below 60); elevated diastolic blood pressure.

Skin and hair: dry skin; hair loss; facial puffiness — especially around the eyes in the morning.

Reproductive: menstrual cycle irregularities; difficulty conceiving.

Diagnosis: TSH Is the Key Test

Diagnosis uses a thyroid panel, with TSH (thyroid-stimulating hormone) at its center.

TSH is the pituitary hormone that controls the thyroid. When T4 drops, the pituitary pumps out more TSH — like a thermostat turning up the heat when temperature falls. This is why TSH rises before T4 drops below normal.

Marker	Normal	Subclinical hypothyroidism	Overt hypothyroidism
TSH	0.4–4.0 mIU/L	> 4.0 mIU/L	> 10 mIU/L
Free T4	9–20 pmol/L	Normal	Low
Free T3	3.5–6.5 pmol/L	Normal	Low or normal

If Hashimoto's is suspected, anti-TPO antibodies are added.

Subclinical Hypothyroidism: Treat or Watch

Clear indications for treatment: pregnancy or planning pregnancy; pronounced symptoms; significantly elevated anti-TPO antibodies; TSH above 10 mIU/L. Otherwise — individualized decision by the physician.

Treatment: Levothyroxine

The standard is levothyroxine (L-T4), taken daily in the morning on an empty stomach 30–60 minutes before food. Target: TSH 0.5–2.5 mIU/L. TSH is checked 6–8 weeks after any dose change.

Hypothyroidism in Pregnancy

Untreated hypothyroidism in pregnancy poses serious risks to fetal brain development. TSH is checked at the first prenatal visit. First-trimester target: below 2.5 mIU/L.

When to See a Doctor Urgently

TSH above 10 mIU/L — schedule an endocrinologist appointment. Hypothyroid symptoms + pregnancy — without delay. Myxedema coma (loss of consciousness, hypothermia, bradycardia) — call emergency services immediately.

Summary

One test — TSH — gives the answer. If you have characteristic symptoms or risk factors (female sex, age over 35, family history of thyroid disease) — it's worth checking. Treatment is simple, safe, and effective.

This article is for informational purposes only. Interpretation of test results and treatment decisions are the responsibility of a physician.