Causes and Symptoms of Hypothyroidism
Hypothyroidism is a condition in which the production of thyroid hormone by the thyroid gland is diminished, leading to a wide range of symptoms including low metabolic rate, weight gain, somnolence, and sometimes myxedema. 1
Causes of Hypothyroidism
Primary Causes
- Chronic autoimmune thyroiditis (Hashimoto's thyroiditis) - most common cause worldwide 2
- Iodine deficiency - historically the most common cause globally 2
- Iatrogenic causes:
- Post-thyroidectomy
- Radioactive iodine treatment
- Medications (amiodarone, lithium, immune checkpoint inhibitors) 2
- Congenital hypothyroidism - thyroid gland dysgenesis or dyshormonogenesis
Secondary Causes (Central)
- Pituitary dysfunction leading to inadequate TSH secretion
- Hypothalamic dysfunction affecting TRH production 3
Clinical Presentation and Symptoms
Common Symptoms
- Metabolic symptoms:
Dermatologic Manifestations
Gastrointestinal Symptoms
- Constipation
- Decreased appetite 4
Cardiovascular Effects
- Bradycardia
- Mild hypertension (often diastolic)
- Narrowed pulse pressure
- Pericardial effusions in severe cases 1
- Increased risk of dyslipidemia 6
Neuromuscular and Cognitive Symptoms
Reproductive Issues
- Menstrual irregularities
- Decreased fertility 4
- Increased risk during pregnancy for:
- Preeclampsia
- Low birth weight in neonates 7
Voice and Speech
- Voice changes (hoarseness)
- Slow speech 5
Severe Manifestations
- Myxedema coma - life-threatening condition characterized by:
- Profound hypothermia
- Altered mental status
- Respiratory depression
- Hypotension 5
Diagnosis
Diagnosis is primarily based on laboratory testing:
- Elevated TSH with decreased free T4 in primary hypothyroidism
- Low or normal TSH with decreased free T4 in secondary hypothyroidism 3
Clinical Pearls
- Symptoms are often nonspecific and develop gradually, making early diagnosis challenging 5
- Subclinical hypothyroidism (elevated TSH with normal free T4) affects 3-13.6% of women and 0.7-5.7% of men 3
- Untreated hypothyroidism can lead to severe complications including mental retardation and delayed milestones in infants, and heart failure and myxedema coma in adults 4
- Autoimmune thyroid disease occurs in 17-30% of patients with type 1 diabetes 7
- Despite normalization of thyroid function tests with levothyroxine treatment, approximately 10% of patients continue to experience persistent symptoms 2
Early recognition of symptoms and appropriate laboratory testing are essential for timely diagnosis and treatment to prevent progression to more severe manifestations of hypothyroidism.