Hypothyroidism Diagnosis
A 35-year-old woman has fatigue, weight gain, cold intolerance, constipation, and dry skin. Labs: ↑TSH, ↓free T4. What is the diagnosis pattern called?
Primary hypothyroidism (thyroid gland failure).
What is the most common cause of hypothyroidism in iodine-sufficient regions?
Hashimoto thyroiditis.
Which reflex finding is typical in hypothyroidism?
Delayed relaxation phase of deep tendon reflexes.
Newborn with large posterior tongue, umbilical hernia, prolonged jaundice, hypotonia. Most likely diagnosis?
Congenital hypothyroidism
First-line treatment for chronic hypothyroidism?
Levothyroxine (T4).
A 48-year-old man has fatigue and decreased libido. Labs: ↓TSH, ↓free T4, and other pituitary hormones are also low. Where is the lesion?
Pituitary (secondary hypothyroidism).
A patient takes a medication for bipolar disorder and develops goiter, weight gain, and cold intolerance. Which medication is most likely?
Lithium.
Hypothyroidism classically causes what lipid abnormality?
Hypercholesterolemia (↑LDL) due to ↓LDL receptor expression/clearance.
Why do we treat congenital hypothyroidism urgently (within the first weeks)?
To prevent irreversible intellectual disability (thyroid hormone is critical for CNS development).
What is the expected TSH change after starting levothyroxine in primary hypothyroidism?
TSH should decrease
A 30-year-old woman 4 months postpartum has palpitations and anxiety that resolved, then develops fatigue and constipation. Labs now: ↑TSH, ↓free T4. What is the most likely diagnosis?
Postpartum thyroiditis (transient hyper → hypo phases).
A patient treated for Graves disease later develops weight gain and cold intolerance with ↑TSH, ↓free T4. What caused their hypothyroidism?
Iatrogenic hypothyroidism (e.g., radioactive iodine ablation or thyroidectomy).
A patient with hypothyroidism has hoarseness, enlarged tongue, and nonpitting edema. What is the underlying mechanism of this edema?
Glycosaminoglycan (mucopolysaccharide) deposition → myxedema.
Newborn screen shows ↑TSH. What does that screening pattern suggest?
Primary congenital hypothyroidism (thyroid dysgenesis/dyshormonogenesis)
Two patients present with weight change and fatigue.
Patient A: weight loss, palpitations, tremor
Patient B: weight gain, constipation, dry skin
Which lab pattern best matches each patient?
Patient A (hyperthyroidism): ↓TSH, ↑free T4 (±↑T3)
Patient B (primary hypothyroidism): ↑TSH, ↓free T4
A 28-year-old woman has fatigue and weight gain. Labs: ↑TSH, ↓free T4. Which antibody is most commonly associated with this condition?
Anti–thyroid peroxidase (anti-TPO) (Hashimoto thyroiditis).
A patient on amiodarone develops hypothyroid symptoms. What key feature of amiodarone helps explain thyroid dysfunction?
High iodine content + effects on thyroid hormone metabolism (can cause hypo or hyper).
A patient with untreated hypothyroidism presents with confusion, hypothermia, bradycardia, hypotension, hypoventilation. What is the diagnosis and first-line management concept?
Myxedema coma; treat with IV levothyroxine (± liothyronine per institution), stress-dose steroids if concern for adrenal insufficiency, and supportive care.
A newborn has congenital hypothyroidism due to thyroid dysgenesis. What embryologic structure gives rise to the thyroid follicular cells?
Endodermal diverticulum from the floor of the primitive pharynx (thyroglossal duct path).
A patient with bradycardia, dry skin, and weight gain has ↑TSH, normal free T4. What is the diagnosis and typical approach?
Subclinical hypothyroidism; treat depending on TSH level, symptoms, pregnancy status, and anti-TPO positivity.
A critically ill ICU patient has ↓T3, normal/↓T4, normal/↓TSH. They are hypothermic and bradycardic but have sepsis. What explains the thyroid labs?
Euthyroid sick syndrome (decreased peripheral conversion; do not treat with thyroid hormone unless true hypothyroidism).
A 40-year-old woman has painless goiter, fatigue, constipation. Labs: ↑TSH, ↓free T4. Anti-TPO positive. Histology shows Hurthle cells and lymphoid aggregates with germinal centers. Diagnosis?
Hashimoto thyroiditis.
A child is short with delayed puberty and bone age less than chronological age. They have constipation, fatigue, and dry skin. What hormone deficiency explains delayed bone maturation?
Thyroid hormone deficiency (needed for normal growth and bone maturation).
A newborn has hypothyroidism and a midline neck mass that moves with swallowing and tongue protrusion. What is the diagnosis and key complication?
Thyroglossal duct cyst; can become infected and may contain ectopic thyroid tissue.
A patient has tremor, weight loss, palpitations. Labs: ↓TSH, ↑T3/T4. Another patient has constipation, weight gain, cold intolerance. Labs: ↑TSH, ↓T4. What receptor type do thyroid hormones bind, and how does that relate to onset?
Intracellular nuclear receptor (transcription factor) → slower onset, long-lasting gene-expression effects.