Hypothyroidism

• Primary hypothyroidism (thyroid gland involved) ➜ High TSH
  • Low thyroxine/tetraiodothyronine (T4)
  • Low triiodothyronine (T3)
• Secondary (pituitary involved): low thyroid stimulating hormone (TSH)
• Tertiary (hypothalamus involved): low thyrotropin-releasing hormone (TRH)

• Primary hypothyroidism: insufficient thyroid hormone production
  • Hashimoto thyroiditis
    • The most common cause of hypothyroidism in iodine-sufficient regions
    • Associated with other autoimmune diseases (e.g., vitiligo, pernicious anemia, type 1 diabetes mellitus, and systemic lupus erythematosus)
  • Postpartum thyroiditis (subacute lymphocytic thyroiditis)
  • De Quervain thyroiditis (subacute granulomatous thyroiditis): often subsequent to a flu-like illness
  • Iatrogenic: e.g., post thyroidectomy, radioiodine therapy, antithyroid medication (e.g., amiodarone, lithium)
  • Nutritional (insufficient intake of iodine): the most common cause of hypothyroidism worldwide, particularly in iodine-deficient regions
• Secondary hypothyroidism: pituitary disorders (e.g., pituitary adenoma) ➜ TSH deficiency ➜ T4 & T3 deficiency
• Tertiary hypothyroidism: hypothalamic disorders à TRH deficiency ➜ TSH deficiency ➜ T4 & T3 deficiency
  • Increased TRH levels will stimulate the release of prolactin

• Symptoms related to decreased metabolic rate
  • Fatigue, decreased physical activity
  • Cold intolerance
  • Decreased sweating
  • Hair loss, brittle nails, and cold, dry skin
  • Weight gain (despite poor appetite)
  • Constipation
  • Bradycardia
  • Hypothyroid myopathy, myalgia, stiffness, cramps
  • Woltman sign: a delayed relaxation of the deep tendon reflexes, which is commonly seen in patients with hypothyroidism, but can also be associated with advanced age, pregnancy, and diabetes mellitus.
  • Entrapment syndromes (e.g., carpal tunnel syndrome)
• Symptoms related to generalized myxedema
  • Doughy skin texture, puffy appearance
  • Myxedematous heart disease (dilated cardiomyopathy, bradycardia, dyspnea)
  • Hoarse voice, difficulty articulating words
  • Pretibial and periorbital edema
  • Myxedema coma
• Symptoms of hyperprolactinemia
  • Abnormal menstrual cycle (esp. secondary amenorrhea; or menorrhagia)
  • Galactorrhea
  • Decreased libido, erectile dysfunction, delayed ejaculation, and infertility in men

Further tests could be used to determine the exact cause of hypothyroidism

• Antibody testing ➜ Thyroglobulin and thyroid peroxidase antibodies (TPOs):
  • Consistent with autoimmune hypothyroidism
• Imaging studies:
  • Ultrasonography: rarely used but can help in distinguishing asymmetric goiter in Hashimoto’s thyroiditis from a nodule/multinodular goiter
  • Brain imaging:
    • CT or MRI
    • Part of workup for central hypothyroidism (secondary and tertiary hypothyroidism)
    • Assess pituitary gland, hypothalamus, and surrounding areas.

• L-thyroxine replacement
• L-thyroxine replacement in subclinical hypothyroidism if:
  • TSH ≥ 10 mU/L
  • TSH 7.0–9.9 mU/L in asymptomatic patients < 70 years
  • TSH above the upper limit of normal to 6.9 mU/L in symptomatic patients < 70 years
• For central hypothyroidism:
  • Thyroid replacement
  • Treat other concomitant hormone deficiencies, if present.

• Myxedema coma
• Primary thyroid lymphoma (Hashimoto thyroiditis is the most common cause of hypothyroidism and the only known risk factor for primary thyroid lymphoma)
• Carpal tunnel syndrome
• Increased cardiovascular risk (Hypothyroidism is associated with hypercholesterolemia, which in turn increases cardiovascular risk.)

• It is an autoimmune disorder leading to destruction of the thyroid cells and thyroid failure leading to hypothyroidism.
• The gradual clinical course of Hashimoto’s thyroiditis starts with a transient hyperthyroid state (“hashitoxicosis”) followed by subclinical hypothyroidism then progression to overt hypothyroidism occurs, which is permanent.
• Hashimoto’s thyroiditis, or chronic lymphocytic thyroiditis, is the most common cause of hypothyroidism in iodine-sufficient regions
• More common in women than men: 10–20:1 ratio