Overview of Hypothyroidism

Hypothyroidism Overview

• Hypothyroidism is a condition where the thyroid gland produces insufficient thyroid hormones (TH).
• It's the most common thyroid dysfunction, affecting a significant portion (0.1% to 2%) of the US population.
• This condition is more prevalent among women and the elderly.

Types of Hypothyroidism

• Congenital: Develops prenatally and presents at birth.
• Acquired: Develops later in life.
  • Primary: The most common type, stemming from thyroid gland failure.
  • Central (secondary): Less frequent, caused by pituitary or hypothalamic failure to trigger normal thyroid function.
  • Subclinical: Mild thyroid failure; characterized by elevated TSH levels, but normal T4 levels. Often doesn't require treatment.

Hypothyroidism Pathophysiology (Congenital)

• Congenital Hypothyroidism: Results from:
  • Lack of thyroid gland development
  • Failure of appropriate thyroid hormone synthesis
  • Problems with TSH secretion
• In Utero: Maternal T4 crosses the placenta, but untreated newborns experience lack of TH production/secretion.
• Presentation: Newborn appears normal initially. Untreated, this lack of TH leads to:
  • Impaired growth
  • Mental retardation (cretinism)
• Screening: Crucial for early diagnosis and intervention.

Hypothyroidism Pathophysiology (Acquired)

• Causes of Acquired Hypothyroidism: Diverse and include:
  • Autoimmune thyroiditis (Hashimoto's disease)
  • Destruction of thyroid gland
  • Deficient synthesis of TH
  • Impaired secretion of TSH
  • Central (secondary/tertiary) hypothyroidism
  • Pituitary/hypothalamic failure leading to insufficient TRH secretion
  • Iodine deficiency (rare, now less common due to iodized salt)
  • Surgical removal of thyroid gland
  • Radiation therapy for hyperthyroidism
  • Medications
  • Genetic defects
• Consequence: Loss of thyroid tissue results in lower circulating TH levels, causing impaired normal function.

Hypothyroidism Clinical Manifestations

• Symptoms: Hypothyroidism affects many bodily systems, leading to symptoms like:
  • Fatigue, weakness, lethargy
  • Cold intolerance
  • Constipation
  • Dry skin, course hair
  • Impaired reproduction
  • Impaired memory
  • Periorbital edema (swelling around eyes)
  • Muscle wasting (loss of muscle mass/strength)
  • Myxedema (accumulation of protein-carbohydrate complexes in tissues)
  • Goiter (enlarged thyroid gland)
• Myxedema: Accumulation of protein-carbohydrate complexes in tissues. This leads to water retention in tissues, resulting in visible swelling (especially in face, hands and feet)

Hypothyroidism Diagnostic Criteria

• History and Physical Examination: Essential for evaluating initial cues, including patient's symptoms and physical characteristics
• Laboratory Studies:
  • Elevated TSH levels (typically)
  • Low free T4 levels (typically)
  • Thyroid uptake to detect gland function/activity
  • Thyroid autoantibodies to diagnose conditions like Hashimoto's disease

Hypothyroidism Treatment

• Lifelong Hormone Replacement Therapy: Essential to maintain normal hormone levels
• Levothyroxine: Synthetic TH commonly prescribed
• Goal: Normalize T3, T4, and TSH levels in the body
• Clinical Sign Alleviation: The hormone therapy helps address symptoms like fatigue, weakness, lethargy and others