A 44 yo woman requests thyroid testing. She has chronic fatigue, which she attributes the stress of being a single mother and having two jobs. Her medical history is notable for depression which is now controlled. Her mother has hypothyroidism and her father has coronary artery disease. Her only medication is fluoxetine. On exam her blood pressure is 135/85, pulse 64/min, and BMI 26.1. Her thyroid gland is not enlarged but is firm in consistency. Her skin is dry. Her reflexes are normal. Labs: CBC nl, BMP nl, cholesterol 235, triglycerides 118, HDL 45, LDL 166, TSH 13 mU/L, repeat TSH after 6 weeks 14 mU/L, free T4 1.0 ng/dL.
Which of the following clinical benefits will she likely experience in response to starting thyroid hormone replacement therapy?
A. Weight Loss
B. Reduced blood pressure
C. Increased HDL
D. Decreased LDL
E. Increased lean body mass
This patient has subclinical hypothyroidism. Her TSH is elevated and T4 is still within the normal reference range. Patients with a TSH above 10 mU/L experience a decrease in their LDL cholesterol with thyroid hormone replacement therapy. The other answer choices in this question did not show any significant change after treatment and if the TSH is below 10, there is no significant change in the LDL after starting thyroid hormone replacement.
TSH (0.5-5 mU/L) main test for thyroid function, misleading results in some pituitary diseases (require MRI if TSH too low)
Free thyroxine (0.8-1.8 ng/dL) use to evaluate thyroid function
Tree T3 (1.5-7 pmol/L) if suspect T3 thyrotoxocosis
serum thyroid stimulating immunoglobulin (expensive test) used to diagnose Graves disease but usually not needed
Toxic multinodular goiter
Exogenous T4, T3
Thyrotoxicosis: check TSH and T4, usually see a supressed TSH if primary thyroid gland overproduction
See normal or elevated TSH if primary pituitary tumor
If TSH is undetectable and T4 is normal, check T3 as can have T3-thyrotoxicosis
Next test is the nuclear medicine 24 hour RAIU and thyroid scan
Shows where the thyroid gland uptake is occuring
Contraindicated in pregnancy and breast feeding
Most common cause in the US
Have unregulated production of T3 and T4 due to autoantibodies to the TSH receptor.
Treat with antithyroid drugs: methimazole 20-30mg daily, propylthiouracil 200 to 300 mg divided 3 times daily (only 50% cure rate after 1 year of therapy)
These medications can cause agranulocytosis, hepatic necrosis or vasculitis but rare (<0.5%)
Radioactive iodine ablation: do not use with severe ophthalmopathy as this worsens for 2-3 months after treatment
Exophthalmic ophthalmoplegia also is known as Graves ophthalmopathy and infiltrative ophthalmopathy.
This refers to weakness of external ocular muscles and exophthalmos from Graves disease.
Strabismus and diplopia may be present, as well as pain and lid retraction.
The term infiltrative ophthalmopathy refers to ocular muscle histology that suggests an autoimmune process: prominent fibroblastic tissue, degenerated fibers, and infiltration of lymphocytes, mononuclear leukocytes, and lipocytes.
Toxic multinodular goiter
Thyroid scan shows areas of suppressed activity and multiple areas of increased uptake
Treat with antithyroid medications but never get remission after the medications are stopped
Treatment of choice is RAIU, usually the non-nodular thyroid tissue recovers normal function but sometimes patients become hypothyroid
Treat with thyroidectomy if large goiter that is compressive, see suspicious “cold” nodules, patient intolerant to antithyroid meds or refuses radioiodine treatment
Toxic adenoma or “hot” nodules
Amount of thyroid hormone produced correlates to the adenoma size, do not see hyperthyroidism until nodule is >3cm in size
Treat with hemithyroidectomy or radioiodine
See low RAIU due to transient thyroid damage
Postpartum thyroiditis occurs in 10% of pregnancies
If TSH persistently suppressed, perform thyroid scan with RAIU
If TSH <0.1 mU/L cardiac arrhythmia risk is high so treat when TSH at this level
No, just hypothyroid
Hypothyroidism, most common cause is Hashimotos disease (in the US)
Subclinical hypothyroidism: elevation of serum TSH level caused by decrease in serum T4 but within the normal range. Most of these patients have Hashimotos thyroiditis, but not all:
Same causes as for subclinical hyperthyroidism (see previous slide)
Consensus is to treat with TSH >10 due to lipid improvement, and possibly bone density improvement
Goal is to treat to prevent progression to overt disease and not to overtreat (esp older patients)
Thyroid binding globulin doubles due to estrogen increase
Women with normal thyroid glands incrase T4 and T3 production to maintain normal free T4 levels but hypothyroid women cannot so replacement needs to be increased 50% to 75% and after delivery the dose can be decreased to the pre-pregnancy level
Poorly controlled hyperthyroidism in pregnancy leads to pre-eclampsia, CHF in mother, fetal death and low infant birth weight, monitor regularly in pregnancy
Graves disease is most common cause of hyperthyroidism in pregnancy but b-hcg can also stimulate the thyroid so this is when the Ig test is done as radioiodine is contraindicated
TSH is suppressed in first and second trimesters, no treatment needed
Patient compliant with medication and despite increased doses of thyroid still not therapeutic consider malabsorption (e.g. celiac disease)
Pendreds syndrome: autosomal recessive condition accounting for up to 10% of hereditary deafness. Pt’s have sensorineural hearing loss that occurs as children due to dysplasia of the cochlea. Pt’s also have goiter associated with the disorder, occuring in late childhood. MRI or CT shows a cochlea with too few turns or large vestibular aqueducts
Mccune –Albright syndrome-hyperthyroidism, café-au-lait spots, and polyostotic fibrous dysplasia
Thyroid nodules detected in up to 25% of adults by high-resolution ultrasound
Evaluate thyroid nodules with TSH, T4 and FNA biopsy
Multinodular goiter may extend substernally compressing trachea, esophagus, and great vessels of the neck
Thyroid cancers-”cold” nodules
Papillary (75%-80%), marker is thyroglobulin, lymphatic spread, 98% 10-year survival
Follicular (15%-20%), marker is thyroglobulin, hematogenous spread, 92% 10-year survival
Medullary (<5%), markers calcitonin and CEA, lymphatic and hematogenous spread, 80% 10-year survival
Anaplastic (<5%), no marker, direct extension, 13% 10-year survival
MEN type 2a: medullary thyroid cancer, hyperparathyroidism, pheochromocytoma
MEN type 2b: medullary thyroid cancer, pheochromocytoma, mucosal neuromas, marfanoid body habitus
Papillary and follicular thyroid cancers are treated with thyroidectomy followed by ablation with radioactive iodine
Medullary thyroid cancer is made up of C-cells so does not take up iodine, treat with resection
Anaplastic thyroid cancer needs to be resected
The mortality rate of thyroid storm can be as high as 20-40%. The symptoms usually are exaggerated manifestations of the symptoms seen in hyperthyroidism; a superimposed infection and the stress associated with it would exacerbate the symptoms. Fever, abdominal pain, delirium, and psychosis can occur. The patient may become obtunded. Thyroid storm should be suspected in any patient with severe hyperpyrexia, tachycardia, and a goiter.
Withdrawal of antithyroid meds
Iodinated contrast dyes
Massive thyroid hormone overdose
Cardiac: tachycardia, hypertension, high-output cardiac failure, and a propensity to develop cardiac arrhythmias.
Neuro: irritability and restlessness in thyrotoxicosis progress to severe agitation, delirium, seizures, and coma.
GI: diarrhea, vomiting, jaundice, and abdominal pain,
Propylthiouracil: blocks new hormone synthesis and blocks T4 to T3 conversion (may also use methimazole but does not inhibit conversion)
Propranolol: blocks T4 to T3 conversion at 60-80mg q4h (may also use esmolol)
Iodine solution: start 1 hour after antithyroid drugs, blocks new hormone synthesis and hormone release (can use lithium carbonate if pt allergic to iodine)
Hydrocortisone: blocks T4 to T3 conversion, prophylaxis against adrenal insufficiency (may also use dexamethasone)