Introduction

Hypothyroidism is a condition in which a person's thyroid hormone production is below normal. Common causes of the disease is chronic autoimmune thyroiditis, post surgery and post radio active iodine.Thyroid disorders are conditions that affect the thyroid gland. There are specific kinds of thyroid disorders that includes hypothyroidism, hyperthyroidism, goiter, thyroid nodules and thyroid cancer.

Risk Factors

• Female sex

• Age > 60 years

• Family history of thyroid disease

• Autoimmune diseases (type 1 diabetes, vitiligo, rheumatoid arthritis)

• Previous thyroid surgery

• Radioactive iodine therapy

• Postpartum period

• Iodine deficiency or excess

• Medications (lithium, amiodarone, interferon)

• Down syndrome or Turner syndrome

• History of neck irradiation

Signs and Symptoms

Symptoms depend on severity and duration and usually develop gradually:

• Fatigue and lethargy

• Cold intolerance

• Weight gain

• Dry rough skin

• Hair loss or thinning

• Constipation

• Depression

• Memory impairment

• Hoarse voice

• Bradycardia

• Menstrual irregularities

• Infertility

• Puffy face and periorbital swelling

• Increased cholesterol levels

• Delayed relaxation of deep tendon reflexes

Severe untreated hypothyroidism may lead to myxedema coma, a life-threatening emergency.

Diagnostic Criteria

• Primary hypothyroidism: High TSH + Low Free T4

• Subclinical hypothyroidism: High TSH + Normal Free T4

• Central hypothyroidism: Low/normal TSH + Low Free T4

Diagnosis is confirmed by thyroid function blood tests.

Diagnostic symptoms

The symptoms depend on the deficiency of thyroid hormone, but can include:

• Increased cholesterol levels

• Depression

• Fatigue

• Hair loss

• Memory loss

• Dry, rough skin

• Constipation

• Hoarse voice

Investigations

• Serum TSH (first-line test)

• Free T4 (FT4)

• Thyroid peroxidase antibodies (TPO Ab)

• Lipid profile

• Complete blood count

• Thyroid ultrasound if goitre or nodules present

Management

Monitoring

• TSH monitoring 6–8 weeks after any levothyroxine dose change, and yearly life–long monitoring once euthyroidism is achieved (target TSH 0.2–4.0 um/l). FT4 can be measured in early stages of treatment.

• In patients with central hypothyroidism, assessments of serum free T4 should guide therapy and targeted to exceed the mid normal range value for the assay being used.

• Wait for TSH equilibration – TSH equilibration requires eight to 12 weeks after any thyroxine dosage change. Once a stable dose is achieved – yearly TSH is sufficient.

In Pregnancy

When the elevation of the TSH level is confirmed, free T4 should be measured in order to classify the hypothyroidism as clinical or overt (OH) and subclinical (SH).

• TSH > 2.5–10.0 mU/L with normal free T4: SH

• TSH > 2.5–10.0 mU/L with low levels of free T4: OH

• TSH ≥ 10.0 mU/L, despite the level of free T4: OH

Women in reproductive period should be euthyroid before conceiving, as the hypothyroidism is associated with neural development. Dose may be doubled during pregnancy and returned to normal dose after delivery.

Non-Pharmacological Management

• Adequate iodine intake (avoid excess)

• Lifelong medication adherence education

• Weight management and healthy diet

• Avoid taking medication with iron, calcium, soy, or high-fiber meals

• Control cardiovascular risk factors

Indications for Treatment

• TSH level persistently > 10 mU/L; treat all patients due to increased likelihood of progression to overt disease and a higher risk of congestive heart failure, cardiovascular disease and mortality.

• TSH levels (4.5–10 mU/L); consider treatment in patients younger than 65 with increased cardiovascular risk (e.g., previous cardiovascular disease, hypertension, documented diastolic dysfunction, atherosclerotic risk factors (dyslipidaemia, diabetes mellitus, smoker), goitre, positive antithyroid peroxidase antibodies, evidence of autoimmune thyroiditis by ultrasound, pregnancy, or infertility), particularly when TSH level is persistently > 7 mU/L.

• Levothyroxine therapy could be considered also for symptomatic middle-aged patients for a short period of time. If a clear beneficial effect is observed, levothyroxine therapy could be maintained.

• Persistently mildly increased TSH levels (4.5–10 mU/L) with positive Thyroid Antibody and thyroid sonographic findings typical of autoimmune thyroiditis.

Pharmacological

Indications for Treatment

Treat all patients if:

• TSH persistently >10 mU/L

Consider treatment if TSH 4.5–10 mU/L with:

• Cardiovascular risk factors

• Positive TPO antibodies

• Goitre

• Symptoms suggestive of hypothyroidism

• Pregnancy or infertility

Therapeutic trial may be given in symptomatic middle-aged patients.

Pharmacological Treatment

First-line: Levothyroxine (L-T4)

Initial dose:

• Overt hypothyroidism: 1.6–1.8 µg/kg ideal body weight

• Subclinical hypothyroidism: 1.1–1.2 µg/kg

Special populations:

• Elderly or heart disease: start 12.5–25 µg/day and titrate slowly

Administration:

• Take on empty stomach 30–60 minutes before breakfast

• Alternatively at bedtime ≥3 hours after meal

• Avoid iron, calcium, and antacids simultaneously

Important notes:

• Routine T4 + T3 combination not recommended

• No evidence for thyroid extracts or iodine supplements

• Adjust dose with weight change, aging, or pregnancy

Prevention

• Screen high-risk individuals

• Monitor thyroid function in pregnancy

• Avoid unnecessary iodine supplementation

• Monitor patients on lithium or amiodarone

• Postpartum screening in high-risk women