Thyroid Flashcards
Increased uptake RAI
- Hyperthyroidism due to Graves, multinodular goiter or thyroid adenoma
- Goitre
- Early-stage of Hashimoto thyroiditis
- Iodine deficiency
- TSH-producing adenoma
- The recovery phase from subacute, silent, or postpartum thyroiditis
- Pregnancy
- Lithium carbonate therapy
- Withdrawal of antithyroid medication
- Rebound after the suppression of thyrotropin
- Congenital defects of thyroid hormone synthesis
- Thyroid cancer (papillary or follicular)
- Trophoblastic disease
- TH resistance
Decreased uptake RAI
- Primary hypothyroidism (for example in congenital hypothyroidism)
- Central hypothyroidism
- Destructive thyroiditis
–Subacute thyroiditis
–Silent thyroiditis
–Postpartum thyroiditis
–Palpation thyroiditis
-Excess iodine
-Dietary supplements
-Radiological contrast
-Medications
–Amiodarone
–Antithyroid drugs
–Perchlorate
–Thiocyanate
–Sulphonamides
–Sulphonylurea
–High-dose glucocorticosteroids
–Topical iodine
-Post-thyroidectomy
-External neck radiation
-Thyroid cancer (nodule more likely to be malignant if “cold” nodule) - Struma Ovarriii
Teratogenic effects of MMI
- cutis aplasia (classic)
- choanal aresia
- esophageal atresia
- omphalocele
- VSD
Reasons for false negative CH NBS
- Central hypothyroidism
- Prematurity (may have delayed TSH increase)
- Low birth weight
- Monozygotic twin (mixing of fetal blood)
- Dopamine therapy (rapidly decreases TSH release)
- Acute Illness
false positive CH NBS
Blood sample is drawn too early, prior to 24hrs of life
1 cause of hypothyroidism worldwide
iodide deficiency
most common thyroid dyshormonogenesis cause
organification defect
Hemangiomas effect on thyroid?
consumptive hypoT
type 3 deiodinase
can be severe hypo
hemangioma could be not visible - ex liver
Pendred syndrome
PDS gene
SLC26A4 gene
defect in transport of I to colloid
presentation: goitre, later childhood
10% have SNHL
causes of poor neurodevelopmental outcomes that are associated with CH
- Late diagnosis
- Late initiation of treatment
- Undertreatment
- Overtreatment
- Prolonged time taken to normalize of thyroid function (TSH)
- Poor attendance of clinic visits
Poor control during first year of life
Associated markers for poor neurodevelopmental outcomes, CH severity:
○ Initial T4
○ Initial TSH
○ Bone immaturity
§ Ie: absent knee epiphyses at term
○ Etiology (ie: thyroid agenesis)
○ Parental education
○ Rural setting
○ Access to NBS program
goal for tx of CH
TSH - upper half of the reference range during the first 3 years of treatment
characteristic of hasimoto
- Characterized by lymphocytic infiltration of the thyroid gland, which results in thyromegaly
neonatal signs of hypothyroidism
○ macroglossia
○ umbilical hernia
○ large anterior fontanelle with wide sutures
○ jaundice
○ cool to touch
○ hypotonia
○ delayed reflexes
Drugs that interfere w thyroid function - need to increase Synthroid
Inhibition of levothyroxine absorption (will need more!)
○ Iron
○ Calcium
○ Soy
○ PPI
○ Aluminum hydroxide
○ Colestyramine
○ Colestipol
○ Sucralfate
○ Raloxifene
Increased hepatic metabolism (will need more!)
○ Phenobarbitol
○ Phenytoin
○ Carbamazepine
○ Rifampin
○ TKI (Imatinib, axitinib, motesanib, vandetanib)
Rexinoids
Increased thyroxine binding globulin levels (will need more - more T4 bound to TBG so less is free)
○ Estrogen
○ Raloxifene
○ Tamoxifen
○ Methadone
○ Mitotane
Fluorouracil
Drugs that interfere w thyroid function - need to decrease Synthroid
Decrease hepatic metabolism (will need less!)
○ Metformin (not great evidence)
Inhibition of 5’ deiodinase
○ Propylthiouracil
○ Methimazole
○ Propranolol
○ Glucocorticoids
○ Iodide
Decreased thyroxine binding globulin levels (will need less!)
* Androgens
* Glucocorticoids
* Nicotinic acid
effect of amiodarone on TFT
- inhibiting TH entry into peripheral tissues
- inhibiting type I 5’-deiodinase activity which converts T4 to T3 and reverses T3 to T2. (This inhibition may continue months after amiodarone withdrawal.)
- inhibiting type II 5’-deiodinase which converts T4 to T3 in the pituitary
- failure to escape from the Wolff-Chaikoff effect
- precipitating or exacerbating preexisting organ-specific autoimmunity in susceptible individuals, such as those with autoimmune thyroiditis
dysregulating thyroid hormone synthesis, especially in patients with thyroid nodules or goiter.
effector lithium on thyroid function
- inhibits TH synthesis and secretion
- usually hypothyroid
- increased AITD
v rarely hyperthyroid
Cystinosis
- what is it
-features
Lysosomal storage dz
Photophobia
Renal problems
Hypothyroidism
Labs in hypoT
- Hypercholesterolemia (↑ LDL)
- Hyponatremia (increased total body water)
- Anemia (↓ erythropoietin, ↓ oxygen requirement)
- Elevated creatinine kinase and LDH (from skeletal muscle)
- Reduced GFR
- Elevated liver transaminases
Exam hypoT
- Reduced heart rate and decreased cardiac contractility
- Delayed relaxation phase of DTRs
- Dry skin (↓ sweat and sebaceous gland activity)
- Periorbital puffiness, non-pitting edema (hyaluronic acid)
Myxedema - exam
-Altered mentation
-Alopecia
-Bladder dystonia and distension
-Cardiovascular
–Elevated diastolic blood pressure—early
–Hypotension—late
–Bradycardia
-Delayed reflex relaxation
-Dry, cool, doughy skin
-Gastrointestinal
–Decreased motility
–Abdominal distension
–Paralytic ileus
–Fecal impaction
–Myxedema megacolon—late
-Hypoventilation
-Hypothermia
-Myxedematous face
–Generalized swelling
–Macroglossia
–Ptosis
–Periorbital edema
–Coarse, sparse hair
-Non-pitting edema
Myxedema labs
-Anemia
-Leukopenia
-Elevated CK
-Elevated creatinine
-Elevated transaminases
-Respiratory
-Hypercapnia
-Hypoxia
-Respiratory acidosis
-Hyperlipidemia
-Lytes & glucose:
–Hypoglycemia
–Hyponatremia
tx myxoedema coma
- ICU
- ABCDE
- Levothyroxine
- Steroids (until AI can be rules out)
=/- Abx if concern infection
why does TSH def happen AFTER starting GH tx?
Thought to be due to increased somatostatin secretion in response to pulsed doses of GH
Endo abnormalities in acquired hypoT
- Elevated prolactin
○ Due to TRH stimulation from the hypothalamus - Delayed puberty / irregular periods
○ Altered and blunted LH pulsatility
○ Elevated prolactin - Pseudoprecocious puberty (van Wyk-Grumbach syndrome)
- Decreased and impaired spontaneous GH secretion
○ Need TH for GH secretion!!!
(That’s why you need to check TFTs before GH stim!!)
TSHR mutations?
Activating somatic mutations - solitary or multiple hyperfunctioning adenomas
Activating germline mutation – congenital hyperthyroidism (mimics neonatal Graves)
Inactivating mutation - TSH resistance
- with uncompensated or compensated hypothyroidism
TSH resistance
TSHR
GNAS
TSHR: can be complete, mod or mild resistance
GNAS: PHP
TSH secreting adenoma
- pres
- lab
Pres: Mild thyrotoxicosis and goiter
May have other pit def
Lab: high fT4, T3, and normal or high TSH
Molar ratio of TSH α subunit: TSH >5.7 is usually diagnostic of the presence of a TSH-secreting pituitary adenoma
HyperT DDx
- Graves autoimmune hyperthyroidism
- Autonomously functioning (hot) nodule
- Toxic Multinodular goitre
- Hashitoxicosis
- Subacute (viral) thyroiditis
- Acute thyroiditis
- Familial non-autoimmune hyperthyroidism
- McCune-Albright syndrome
- TSH adenoma
- Thyroid hormone ingestion
- Ingestion of ground beef (inclusion of strap muscles)
- Struma ovarii
Mimicer: Thyroid hormone resistance (RTH), TBG d/o
Signs of GO
- Lid lag
- Corneal dryness
- Erythema
- Tearing
- Strabismus
- Vision loss
MMI s/e
- Minor adverse effects in up to 20% of patients
- Major side effects : 1%
- Allergic reaction
- Minor S/E
○ Rash
○ Arthritis
○ Myalgia
○ Neutropenia
○ Hypothroidism
○ Elevated LFTs
○ H/a - Major S/E
○ Hepatic necrosis, cholestatic jaundice
○ Stevens-Johnson syndrome
○ Vasculitis
○ Agranulocytosis
BBlockers for Graves
- Propranolol: non selective
– decreases T4->T3 conversion - Atenolol : cardio- selective
Mgmt GO
-Smoking cessation
-Referral to ophthalmologist
-Symptom relief (topical lubrication, etc)
-Rapid normalization of hyperthyroidism
–Avoid RAI
-Mild disease – head elevated at night, and diuretics to decrease periorbital edema
-Prednisone (after RAI) – 0.4mg/kg/d
–reducing the dose by 10 mg every 2 weeks, protects against exacerbation of ophthalmopathy following RAI
-Severe/acute disease
–High-dose corticosteroids
–Weekly pulse of high dose IV methylpred shown to be more effective and less
–If not effective or recurrence after steroids taper external X-ray therapy to retrobulbar area
-If vision is threatened - orbital decompression