Week 3: Hypothyroidism

Question 1

What is the most sensitive test for thyroid status?

Answer 1

• TSH
• sensitive to to minor decrements and rises of Free T4
• because will have a 100 fold change in response to a 2 fold change of free T4

Question 2

Etiologies of hypothyroidism

Answer 2

1. Primary
   - chronic autoimmune (Hashimoto’s thyroiditis)
   - Ablative therapy: 131-I or surgery
2. Secondary
   - pituitary tumors
   - sheehan’s syndrome
   - hypothalamic disease
3. Pharmalogic agents: amiodarone, lithium carbonate, Interferons, interleukins, tyrosine kinase inhibitors
4. Transient
   - subacute thyroiditis
   - post-partum

Question 3

Physiologic response to hypothyroidism

Answer 3

1. Decreased O2 consumption and heat generation
2. reduced b-adrenergic tone
   - decrease in receptor number
   - altered G protein
   - increase in phosphodiesterase activity
3. normal alpha adrenergic tone
   - increased alpha/beta tone
4. peripheral vasoconstriction
   - HTN-diastolic
   - decrease in blood volume

Question 4

Symptoms of hypothyroidism

Answer 4

• arthralgias
• cold intolerance
• constipation
• decreased appetite
• impaired memory
• decreased perspiration
• depression
• dry skin
• fatigue
• hoarseness, lethargy
• menstrual disturbances
• sleepiness
• weight gain, but usually no more than 10% of baseline

Question 5

Signs of hypothyroidism

Answer 5

• bradycardia
• coarse hair
• dry, cool, pale skin
• goiter
• hoarseness
• nonpitting pre-tibial edema
• puffy eyesa nd face
• slow movements
• slow speech
• delayed relaxation of deep tendon reflexes
• thinning of lateral third of eyebrows

Question 6

Hashimoto’s Thyroiditis

Answer 6

• predominant in females 5:1
• gradual onset from adolescence
• cell mediated autoimmune thyroiditis, Th1 response
• early in disease: rubbery, diffuse, gland, euthyroid
• late: atrophic thyroid gland, hypothyroid
• increased frequency with aging

Question 7

Laboratory findings in Hashimotos thyroiditis

Answer 7

• free T4 is low or normal
• TSH is elevated
• Anti TPO positive

Question 8

Rx of hypothyroidism

Answer 8

• L-T4 treatment of ~1.6ug/kg/day (90% of population has serum TSH of 1.0mU/L)
• for older patients, dose should be lower to start with
• decreased dose for those with cardiac disease
• increased dose for pregnancy
• meds that interfere with L-T4: iron, calcium, proton pump inhibitors
• repeat TFTs in 6-8 weeks
• rising T4 value is best gauge of response since TSH lags behind increase T4 levels

Question 9

cretinism

Answer 9

-fetal hypothyroidism and neonatal hypothyroidism leads to severe mental and growth retardation