Differential Diagnosis for Hypothyroidism

The patient's symptoms of constipation, fatigue, dry skin, cold intolerance, and weight gain, along with low T4 and T3 levels and elevated TSH, are indicative of hypothyroidism. Here is a categorized differential diagnosis:

• Single Most Likely Diagnosis

  • Hashimoto thyroiditis: This is an autoimmune condition that is the most common cause of hypothyroidism in areas of the world where iodine intake is adequate. The patient's symptoms and laboratory findings are consistent with this diagnosis, and it is more prevalent in women, especially in the 40-60 age range.

• Other Likely Diagnoses

  • Inadequate dietary intake of iodine: Although less likely in a nurse who presumably has knowledge about nutrition, iodine deficiency can cause hypothyroidism. However, this would be less common in areas with iodized salt and where seafood consumption is part of the diet.
  • Other forms of thyroiditis: While less common than Hashimoto thyroiditis, other forms of thyroiditis (like subacute or silent thyroiditis) could initially present with hypothyroidism, though they often have a different clinical context and may not have the same chronic course.

• Do Not Miss Diagnoses

  • Pituitary or hypothalamic disease: Although rare, diseases affecting the pituitary or hypothalamus (e.g., tumors, infiltrative diseases) can lead to central hypothyroidism, characterized by low T4 and T3 with low or inappropriately normal TSH. Missing this diagnosis could lead to inadequate treatment and potentially severe consequences.
  • Medication-induced hypothyroidism: Certain medications (e.g., amiodarone, lithium) can cause hypothyroidism. Although the patient reports taking no medications, this should always be considered, especially if the clinical picture does not fit a more common diagnosis.

• Rare Diagnoses

  • Riedel thyroiditis: A rare form of chronic thyroiditis characterized by a hard, fibrotic thyroid gland that can cause hypothyroidism. It is less likely given the thyroid is not palpable or tender.
  • Graves disease with a hypothyroid phase: Graves disease typically causes hyperthyroidism, but it can rarely have a hypothyroid phase. However, this would not typically be the initial presentation.
  • Congenital hypothyroidism: Unlikely in a 40-year-old, as it is usually diagnosed in infancy or early childhood.
  • Infiltrative diseases (e.g., sarcoidosis, hemochromatosis): These can affect the thyroid and cause hypothyroidism but are less common and would typically have other systemic manifestations.