Thyroid-function and pathology Flashcards
Function of thyroid hormone
-4B’s: brain maturation, bone growth, B-adrenergic effects (inc B receptors in heart), Basal metabolic rate inc (via inc Na/K-ATPase activity).
Regulation of thyroid hormone
TRH (hypothalmus) stimulates TSH(pituitary) which stimulates follicular cells.
Negative feedback by free T3, T4 to anterior pituitary
Wolff-Chaikoff effect: excess iodine temporarily inhibits thyroid peroxidase –> dec iodine organification –> dec T3/T4 production
Thyroxine-binding globulin
Binds most T3/T4 in blood, only free hormones active. Dec TBG in hepatic failure, steroids. Inc TBG in pregnancy or OCP use (estrogen inc TBG).
Source
Follicles of thyroid, most T3 is formed in target tissues
Hypothyroidism symptoms
- Cold intolerance
- Wt gain/dec appetite
- hypoactivity/lethargy/fatigue/weakness
- constipation
- dec reflexes
- Myxedema (facial/periorbital)
- Dry, cool skin with coarse, brittle hair.
- Bradiacardia, dyspnea on exertion
Labs: inc TSH, dec T3/T4, hypercholesterolemia
Hyperthyroidism symptoms
- Heat intolerance
- Weight loss/inc appetite
- hyperactivity
- Diarrhea
- hyper-reflexia
- Pretibial myxedema
- warm, moist skin and fine hair
- chest pain, palipitations, arrhythmias, inc number/sensitivity of B receptors
Labs: decreased TSH, inc T3/T4, hypocholesterolemia.
Hashimotos
AI disorder (anti-thyroid peroxidase, antimicrosomal and antithyroglobulin abs). Associated with HLA-DR5 and inc risk of non-hodgkins lymphoma.
May be hyperthyroid early in coursedue to throtoxicosis during follicular rupture. Histologic findings: Hurthle cells, lymphoid aggregate with germinal centers. Findings: moderately enlarged, nontender thyroid.
Congenital hypothyroidism (Cretinism)
Severe fetal hypothyroidism due to maternal hypothyroidism, thyroid agenesis, thyroid dysgnesis, iodine deficiency, dshormonogenetic goiter. Infants are screened at birth.
Findings (6 Ps): Pot belly, Puffy face, Protruding umbilicus, Pale, Protuberant tongue, Poor brain development.
Subacute thyroiditis (de Quervain)
Self-limited disease following a flu-like illness. May be hyperthyroid early in course followed by hypothyroid. Histology: granulomatous inflammation, focal destruction. Findings: inc ESR, jaw pain, early inflammation, very tender thyroid, fever.
Riedel Thyroiditis
Thyroid replaced by fibrous tissue. May extend into local structures, mimicking anaplastic carcinoma. Considered manifestation of IgG4 related sytemic disease. Findings: fixed, rock-hard, painless goiter.
Other causes of hypothyroid
Iodine deficiency, goitrogens, Wolff-Chaikoff effect (downregulation in response to inc iodine).
Graves disease
Autoantiboides (IgG) stimulate TSH receptors on thyroid (hyperthyroidism, diffuse goiter), retro-orbital fibroblasts (exopthalmos: proptosis, extraocular muscle swelling) and dermal fibroblasts (pretibial myxedema). Often presents during stress. Dec TSH, decreased/absent menstruation.
