Thyroid Disease for FNP Boards: Hypothyroidism, Hyperthyroidism, and Thyroid Nodules

Clinical High-Yield · 9 min read · April 8, 2026

Hypothyroidism

Causes: Hashimoto's thyroiditis (most common in US), post-thyroidectomy, radioactive iodine treatment, medications (amiodarone, lithium)

Symptoms: Fatigue, weight gain, cold intolerance, constipation, dry skin, hair loss, bradycardia, depression, myxedema (severe)

Diagnosis:

• TSH elevated + free T4 low = primary hypothyroidism
• TSH low + free T4 low = secondary (pituitary) hypothyroidism

Treatment:

• Levothyroxine (T4 replacement)
• Start low, go slow — especially in elderly and cardiac patients
• Monitor TSH every 6–8 weeks until stable, then annually
• Take on empty stomach, 30–60 minutes before food/other medications

Board pearl: Subclinical hypothyroidism (elevated TSH, normal free T4) — treat if TSH >10, symptomatic, pregnant, or planning pregnancy.

Hyperthyroidism

Causes: Graves' disease (most common), toxic multinodular goiter, toxic adenoma, thyroiditis, excessive levothyroxine

Symptoms: Weight loss, heat intolerance, palpitations, tremor, anxiety, diarrhea, exophthalmos (Graves' specific), pretibial myxedema (Graves' specific)

Diagnosis:

• TSH low + free T4/T3 elevated
• Thyroid-stimulating immunoglobulins (TSI) positive in Graves'

Treatment options:

• Antithyroid medications: Methimazole (preferred), propylthiouracil (PTU — preferred in first trimester pregnancy)
• Radioactive iodine (RAI): Definitive treatment; contraindicated in pregnancy
• Thyroidectomy: For large goiter, cancer suspicion, failed medical therapy
• Beta-blockers: Symptom control (palpitations, tremor) while awaiting definitive treatment

Thyroid storm: Life-threatening hyperthyroidism — treat with PTU, beta-blockers, iodine (SSKI), glucocorticoids, and supportive care

Thyroid Nodules

Evaluation:

• TSH first: If low, get thyroid scan (hot nodule = usually benign)
• Ultrasound for all palpable nodules
• FNA biopsy if nodule ≥1 cm with suspicious features

Suspicious ultrasound features (TIRADS high risk):

• Hypoechoic
• Irregular margins
• Microcalcifications
• Taller than wide
• Extrathyroidal extension

Board pearl: Most thyroid nodules are benign. Papillary thyroid cancer is the most common thyroid malignancy — excellent prognosis with treatment.

Thyroid Cancer Screening

No routine screening recommended for average-risk patients. Screen patients with:

• Family history of thyroid cancer or MEN2
• History of head/neck radiation
• Palpable thyroid nodule on exam