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Thyroid Lecture

Thyroid Disorders

Anatomic size of Thryoid About 4 cm high vertically and each lobe is about 2.5cm across
Thyroid examination Visual inspection, landmark identification, palpation, auscultation (for bruits), lymph node examination (cervical and supraclavicular). One side at a time, then the isthmus
How much Thyroxine per day does the thyroid produce? 100mcg; thyroid has a 50 day reserve supply of thyroxine
Thyroid hormone synthesis requires a minimum of ___ mcg of elemental iodine/day 60
Which is more pharmacologically active Thyroid hormone? T3
Endocytosis and degradation of _______ is required to create biologically active thyroid hormones Thyroglobulin
Thyroid hormones are bound to thyroid binding globulin (TBG), transthyretin, or albumin in plasma
TBG is _____ by estrogen and ______ by androgen increased; decreased
TRH is released by the hypothalamus
TSH is released by the anterior pituitary
What provides negative feedback to the hypothalamus? Free T3 and Free T4.
Most common blood tests to determine thyroid function Ultra-sensitive TSH (thyrotropin) and Free T4
Direct test of thyroid function 131-Iodine Uptake; measured at 24 hours; nl is 15-30% of iodine load goes into thyroid
Imaging Thyroid scan, US, CT, MRI, PET
Biopsy Fine Needle Aspiration, open biopsy
What can a thyroid do? Overact, under-perform, enlarge (like a toddler)
Main hyperthyroid symptoms Unintentional weight loss, heat intolerance, palpitations/tachycardia
Brisk DTR relaxation phase is seen in what condition? Hyperthyroidism. Slow with hypo
Common Causes of hyperthyroidism Graves dz, toxic multinodular goiter, toxic nodule, thyroiditis
Graves Disease Autoantibody reacting with the TSH receptor. Symmetric non-tender goiter. Bruit is pathognomonic. Ocular findings, pretibial myxedema
Evaluation of Graves Disease TSH, Free T4 and T3, Thyroid uptake and scan
Eye protuberance in Graves Disease Autoantibody binds to extraocular eye muscles, eyes pushed out, optic nerve can be squished. Difficult to manage. Radiation may be used
Pharmacologic Treatment for Graves Disease Two agents to suppress the thyroid:PTU - 3x/day dosing, pregnant patients must use this oneMethimazole (tapazole)- 1x/day dosingBeta-blockers acn also be used:propanolol or atenolol
Other Treatment for Graves Disease Surgery: subtotal thyroidectomyRadioactive Iodine Ablation: Drink a substance, radioactive iodine goes to thyroid and destroys part of thyroid. Problem is that some pts become hypothyroid.
Favorable Prognosticators for remission of Graves Dz Small goiter, Free T3 predominance, Negative TSI titer, Decrease in goiter size with thionomide therapy
Etiology of Toxic Multinodular Goiter Multicellular autonomous function. Usually in patients >50. Arises from non-toxic multinodular goiter. Exam: enlarged, irregular, nodular thyroid.
Treatment for Toxic Multinodular Goiter Only treatment is Radioactive iodine to knock out nodule. Thyroid stays in tact
Etiology of Toxic nodule Constitutive activation of the TSH receptor through a somatic mutation of the receptor gene. Age: 30-40. Exam: Enlarged, irregular, nodular thyroid, Oncholysis (ring finer). Hot Nodule
Thyroiditis Two types: Subacute (deQuervain's), Silent or painless (Hashitoxicosis). Course: hyper, hypo, euthyroidism
Etiology of subacute thyroiditis Thyroid hormone leakage from destruction the thyroid gland secondary to a viral infection (mumps)
Pain in the thyroid gland and fever is associated with what diagnosis Subacute thyroiditis
Treatment for Subactute thyroiditis Aspirin, NSAIDs, prednisone
Sudden onset of hyperthyroidism that is self-limited and can also be seen post-partum suggests what diagnosis? Silent Thyroiditis. Not a thyroid problem, just leakage. Rx: BB. This is a transient autoimmune dysfunction
Thyrotoxic Crisis (thyroid Storm) Come back to thiss
Hypothyroidism can cause high cholesterol. First address the hypothyroidism
Etiology of Hypothyroidism Primary, Goiterous, Cenral (lack of TSH; pituitary or hypothalamic failure; unusual)
Primary cause for hypothyroidism Hashimoto Thyroiditis; marked by cytotoxic anti-thyroid antibodies. Anti-thyroglobulin in 80-90%
How to treat hypothyroidism Thyroxine replacement
Levothyroxine facts T1/2 is 7 days, 6 weeks to get to equilibrium, dosage is based on ideal body weight. Okay to make up a dose if you miss one. Virtually no AEs
Adjust Levothyroxine in which patients? Elderly (>65), or angina patients; start slower and lower. In pregnant patients, increase dose by 50%
When should patients treated with levothyroxine be assessed? Assess response with TSH after 6weeks; re-assess at 6 months because of euthyroid state increases clearance of t4, then annually
What are the side effects of thyroxine overtreatment? osteoporosis, increased cardiac contractility, increased risk of atrial fibrillation, allergic reaction to dye in tablets
Describe the half life of T3 (Liothyronine) it is short, so patient feels the ups and downs of the drug
Desiccated thyroid is made from pigs and cows. Amount of T3 and T4 is variable
Goiter General term for enlargemet of the thyroid
Nontoxic goiter not caused by neoplastic process or inflammation. Two types: endemic - in more than 10% of pop. , Sporadic - genetic or environmental factors that do not affect the general population
Endemic Goiter Impaired thyroid hormone. Prevalence determined by iodine deficiency
Multinodular Goiter Sporadic, unknown etiology, multifactorial, some genetic connection
Multiple nodules as opposed to a single nodule suggests benign course
______% of the population have thyroid nodules on US 40-60%. Only 5% become palpable, of those 5% are malignant
Benign characteristics of thyroid nodules symptoms of hypo or hyperthyroidism, pain or tenderness over thyroid nodule, Family hx
Suspicious historical features of thyroid nodules recent changes in size, age <20, >70, Male, History of neck irradiation, Previous h/o thyroid cancer, recent changes in voice, breathing or swallowing (recurrent laryngeal nerve), family hx of thyroid malignancy.
Suspicious exam of thryoid nodules firm nodules with irregular shape, fixation to underlying tissues, regional adenopathy
Evaluation of Thyroid nodule TSH, US, FNA (no thyroid scan!)
Size cutoff for watching nodules 1.5 cm
Predictors of histological malignancy of thyroid nodule microcalcifications, blurred margins, size >10mm, hypoechoic, Vascularity (intranodular blood flow on multiple vascular images)
Benign Follicular Cell Tumors Follicular and Hurthle cell adenomas
Papillary Thyroid Carcinoma F:M 4;1, high survival rate, age: 30-50
Follicular Thyroid Carcinoma F:M 2:1, Age>50, more common to have distant metastases (lung and bone)
Medullary Thyroid Carcinoma F:M 1:1, Age>40, Associated with MEN type2, Rx: aggressive surgery
Thyroid cancer staging factors: Tumor size, Tumor characteristics, Metastases, Patient age
Treatment for Thyroid Carcinoma Thyroidectomy by experience surgeon. Papillary <1cm w/o invasion: rx - thyroxine. suppression and follow thyroglobulin (should be low and non) and exam annually.
Hyperthyroid with normal thyroid exam Graves dz or iatrogenic. Possilbe low lying thyroid, consider thyroid uptake scan, consider referral
Graves Dz Symmetric +/- bruit, Rx: anti-thyroid meds, endo referral
Toxic Multi-nodular goiter irregular contour, Rx: TMG - uptake, scan, ablation
Subacute thyroiditis tender, hard, Rx: aspirin
Silent thyroiditis non-tender, firm, Rx: follow
Most common malignant thyroid tumor Papillary Carcinoma; greatest incidence is in adults 40years old or younger, F>M. Least malignant of the thyroid cancers
Created by: ltm12