Thyroid and Parathyroid Flashcards
Which cells are responsible for making Calcitonin?
C cells of the thyroid gland
(parafollicular cells)
Thyroid epithelial cells secrete _______, which is secreted into the lumen of the follicle.
Thyroglobulin
What are the actions of TSH (secreted by the pituitary)?
Increase iodide uptake
Increase activity of thyroid peroxidase
Stimulate synth of thyroglobulin
Determine rate of endocytosis
Increase proportion of T3
If 15% of T3 is secreted by the thyroid gland, where does the other 85% come from?
Converted from T4 by deiodinases
*drugs such as propanalol and glucocorticoids can inhibit deiodinases
Due to their effect on lipid metabolism, thyroid hormone levels are (directly/inversely) proportional to cholesterol and triglyceride levels.
Inversely
*high thyroid hormone = low cholesterol and triglycerides
T/F: Normal levels of thyroid hormone are needed for development of the fetal and neonatal brain?
TRUE
*hypothyroid patients will have decreased mental development
A 7 year old Irish Setter is presented for weight gain, lethargy and hair loss.
Your exam results are as follows:
T: 99.5F
HR: 55bpm
Auscultation: apex beat is weak
Cranial nerve reflexes normal. Bilateral ptosis. Drooping face. Hair loss is symmetrical and patchy.
What do you expect to find on the bloodwork for this patient?
Low T4 AND high TSH (both to confirm dx!!)
High cholesterol
*Lower body temp, bradycardia, weight gain, hair loss, and drooping face are suggestive of hypothyroid disease.
Labwork on the Irish Setter shows increased TSH and decreased T4, confirming primary hypothyroidism. What is the most likely cause?
Lymphocytic thyroiditis
*Lymphocytic destruction of the thyroid gland
You start the Irish Setter on thyroxine and wait 3 months to assess effectiveness. At what intervals should you measure serum T4 to assess the current dose?
Peak (4-6 hours after admin)
Trough (12 hours after admin)
*Monitor peaks and troughs every 3-6 months
What lab result would indicate secondary hypothyroidism?
Decreased TSH and decreased T4
*Pituitary not making TSH
Why do cats get hyperthyroidism so much now, when it was rare prior to 1979?
Polybrominated diphenyl esthers (PBDEs) found in furniture - environmental toxin
Less evidence for food based hypotheses: pop-top cans, giblets/fish/liver, soy, bisphenol-A
A DSH cat is presented for weight loss, hyperactivity, aggression, and urinating on the furniture. The cat has noteable loss of muscle mass and is difficult to work with. On paplation of the ventral neck you feel a lump. What blood test will you recommend?
TT4
*T4 should be high. In up to 10% of cats, T4 is normal due to concurrent euthyroid sick syndrome, which brings the T4 back down (into normal range).
Bloods on the hyperactive DSH show increased T4 levels, confirming hyperthyroid disease. What is the gold standard treatment?
I-131
*Definitive treatment - destroys surrounding tissues within 1mm
The owner of the hyperthyroid cat would rather medicate at home than try radiation. What do you prescribe?
Methimazole
*Can also use Carbimazole but be aware that the active metabolite is methimazole. Carbimazole will require a higher dose to achieve the appropriate level of methimazole in the blood.
What is a significant disadvantage to medically treating hyperthyroidism in cats?
Tumor will continue to grow and may become malignant.
Higher incidence of carcinoma was found in cats medically treated long term.
What are the main advantages and disadvantages to I-131 therapy for hyperthyroidism?
ADV: Kills abnormal cells in any location (ectopic tissue). Serious side effects rare. Cure rate 95%.
DISADV: Cat kept inside for 2 weeks post radiation, and owner can’t cuddle cat for 2 weeks. Waste management.
You take a blood pressure reading on the hyperthyroid cat and find that the cat is hypertensive. Is this expected to resolve with treatment of the thyroid disorder?
Nope. Give Amlodipine in cats with concurrent hypertension.
Hyperthyroid cats are predisposed to what heart condition?
HCM
*Hypertrophic L ventricle, dilated L atrium. Will see arrhythmias. conduction disturbances, or sinus tachycardia on ECG.
What disease are we likely to uncover after treating hyperthyroidism in cats?
Renal disease
What is the MST for cats being treated for hyperthyroid disease?
2-4 years
What happens when PTH binds to osteoblasts?
Increases the activity of osteoclasts and Ca and P are liberated from the bone.
How does PTH increase calcium levels via the kindey?
Blocks reabsorption of phosphate in the proximal tubule, increasing excretion.
This increases absorption of Calcium.
Also, stimulates the production of active Vit D
What facilitates intestinal absorption of Ca++ by stimulating expression of the proteins that transport Ca++ in the lumen?
Vitamin D
What cells secrete calcitonin?
C cells of the thyroid gland
(parafollicular cells)
A 5 year old Labrador presents during the Hills food recall and the owner is worried he might have been overdosed on Vit D. What blood test can you do to determine if the dog currently has hypercalcemia?
ionized calcium
An 8 year old Keeshound presents for lethargy and not eating. He’s been urinating in the house and drinking more. Initial labs show hypercalcemia, which is confirmed with an ionized calcium level. PTH level is also high. An ultrasound of the neck is performed, which shows an enlarged parathyroid gland. Based on the signalment and test results, what is the most likely cause of hypercalcemia in this patient?
Parathyroid adenoma
*Primary hyperparathyroidism. Usually single adenoma. Breeds: Keeshound, GSD, Norwegian Elkhound, Siamese cats.
In a dog with lymphoma, who may be treated with chemotherapy, what treatment for hypercalcemia would be inappropriate?
Glucocorticoids
*useful in treating hypercalcemia otherwise by decreasing calcium absorption, but will reduce absorption of chemotherapy drugs
What hypercalcemia treatment would be particularly useful in patients with multiple myeloma?
Bisphosphonates
*stops Ca++ from being released from the bone
What emergency hypercalcemia treatment has a short term effect and is useful in cases of Vit D toxicosis?
Calcitonin
What is the first step in emergency treatment of hypercalcemia?
Diuresis
*Furosemide when hydrated
A 7 year old toy poodle presents with a history of nervousness, tremors, stiff gait, aggressive behavior, and rubbing at his face. Temperature is 103F and you note an irregular heart beat on auscultation. Labs show a decrease in calcium so you check PTH level, which is also decreased. If the only surgical history on this patient is neuter at 6m, what is the likely cause of the lab results and clinical signs?
Lymphocytic parathyroiditis
*If there is a history of previous thyroidectomy, it would likely be that the parathyroid glands were removed during the surgery.
A Miniature Schnauzer comes in on emergency for a sudden onset of tremors. Labs are assessed and the calcium level is markedly low. What is the emergency treatment for this patient?
10% calcium gluconate IV (slows over 12-20 mins to avoid dysrrhythmias)
*Monitor ECG and temperature
The hypocalcemic Miniature Schnauzer has been stabilized and is ready to go home. What will the maintenance treatment be?
Calcitriol (vit D3) or Calcium supplements
What treatments are used to decrease P and increase Ca in patients with chronic kidney disease?
Phosphorus binder
Calcitriol
In what patients is nutritional secondary hyperparathyroidism usually seen?
Exotics
Growing animals being fed a raw or homemade diet
*Diets low in calcium stimulate PTH secretion
