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Toronto Notes 2019
Thyroid
Endocrinology E23
Thyroid Biopsy
• fineneedleaspiration(FNA)forcytology
■ differentiates between benign and malignant disease
■ best done under U/S guidance
■ accuracy decreased if nodule is greater than 50% cystic, or if nodule located posteriorly in the gland
Table 17. Summary of Diagnostic Testing in Hyperthyroidism and Hypothyroidism
Drugs Affecting Thyroid Function
Thyroid 2010;20(7):763-770
• Lithiumplaysaninhibitoryroleinthyroid
hormone release, resulting in clinical hypothyroidism and goitre.
• Amiodarone-InducedHypothyroidism(AIH): Amiodarone, a class III anti-arrhythmic drug, contains 2 atoms of iodine per molecule and is structurally similar to thyroid hormones, and may exert antagonistic effects on TSH receptors. It is also shown to inhibit type I deiodinases resulting in low T3 and high T4 levels. Amiodarone-induced hypothyroidism occurs in 5-15% of patients
on amiodarone. AIH can also occur in people without pre-existing thyroid dysfunction.
• Amiodarone-Inducedthyrotoxicosis(AIT): occurs in 2-12% of patients on amiodarone. This may be due to either an increased iodine load in patients with previously autonomous thyroid (Graves’ disease, toxic multinodular goitre), or amiodarone-induced destructive thyroiditis.
Signs and Symptoms of HYPERthyroidism
Tremor
Heart rate up
Yawning (fatigued) Restlessness Oligomenorrhea/amenorrhea Intolerance to heat
Diarrhea
Irritability
Sweating
Muscle wasting/weight loss
TSH
Free T4 Antibodies RAIU
Radioisotope Thyroid Scan
Hyperthyroidism
Decreased in 1° hyperthyroidism Increased in 2° hyperthyroidism
Increased in 1° hyperthyroidism Increased in 2° hyperthyroidism
Graves': thyroid stimulating Ig (TSI)
Hypothyroidism
Increased in 1° hypothyroidism Decreased in 2° hypothyroidism
Decreased in 1° hypothyroidism Decreased in 2° hypothyroidism
Hashimoto’s: antithyroid peroxidase, thyroglobulin (TPOAb, TgAb)
Increased uptake
Graves'
Toxic multinodular goitre Toxic adenoma
Decreased uptake Subacute thyroiditis Recent iodine load Exogenous thyroid hormone
Graves': homogenous diffuse uptake
Multinodular goitre: heterogeneous uptake
Toxic adenoma: single intense area of uptake with suppression elsewhere
Thyrotoxicosis
Definition
• clinical,physiological,andbiochemicalfindingsinresponsetoelevatedthyroidhormone
Epidemiology
• 1%ofgeneralpopulationhavehyperthyroidism • F:M=5:1
Etiology and Pathophysiology
Table 18. Differential Diagnosis of Thyrotoxicosis
Disorder
HYPERTHYROIDISM Graves’ Disease Toxic Nodular Goitre Toxic Nodule
THYROIDITIS
Subacute, Silent, Postpartum
TSH
Decreased Decreased Decreased
Decreased
Free T4/T3
Increased Increased Increased
Increased
Thyroid Antibodies
TSI None None
Upto50%of cases (TSI, TPO, Tg)
None
None
None None
None
RAIU
Increased Increased Increased
Decreased (increases once entering hypothyroid phase, when TSH rises)
Decreased
Decreased
Increased Increased
Increased
DO NOT DO THIS TEST IN PREGNANCY
Other
Homogenous uptake on scan
Heterogeneous uptake on scan
Intense uptake in hot nodule on scan with no uptake in the rest of the gland
In classical subacute painful thyroiditis, ESR increased
Common Etiologies
Thyrotoxicosis
Graves’ Disease Toxic Nodular Goitre Toxic Nodule
Thyroiditis
Hypothyroidism
Hashimoto’s
Congenital
Iatrogenic (thionamides, radioactive iodine, or surgery)
Hypothyroid phase of thyroiditis
EXTRATHYROIDAL SOURCES OF THYROID HORMONE
Endogenous (struma ovariae, ovarian teratoma, metastatic follicular carcinoma)
Exogenous (drugs)
Decreased
Decreased
Increased
Increased (T4 would be decreased if taking T3)
Increased Increased
Increased
EXCESSIVE THYROID STIMULATION
Pituitary thyrotrophoma
Pituitary thyroid hormone receptor resistance
Increased hCG
(e.g. pregnancy)
Increased Increased
Decreased