121. Thyroid_parathyroid

Question 1

anatomical differences in dog vs cat thyroid glands

Answer 1

2 glandsdogs: communicate w ventral isthmuscats: lack isthmus, lack caudal thyroid artery

Question 2

components of the carotid sheath

Answer 2

–common carotid artery–internal jugular vein–vagosympathetic trunk

Question 3

blod supply to thyroid gland

Answer 3

cranial and caudal thyroid arteries (caudal is lacking in cats)cranial thyroid artery is the first branch of common carotid arterycaudal thyroid artery branches from brachiocephalic trunk

Question 4

number of parathyroid glands

Answer 4

2 on each gland (4 total)1. extra capsular PTG—cranial (blood supply from cranial thyroid artery)2. intra capsular PTG–caudal and embedded(blood supply from vessels surrounding the parenchyma)variations exist

Question 5

areas where ectopic thyroid tissue can be found

Answer 5

1. along trachea2. thoracic inlet3. mediastinal4. thoracic aorta(base of tongue to base of heart)ectopic parathyroid tissue is uncommon in dogs but up to 50% cats

Question 6

thyroid gland hormones

Answer 6

–requires iodine to produce thyroglobulin (stored in follicles): contains precursors for thyroid hormone synthesis–T4, T3 (lesser extent) released into blood which are larger bound to proteins–T4 major secretory product BUT T3 is the most active form–production of hormones stimulated by TSH release by pituitary/TRH release by hypothalamus

Question 7

parathyroid gland hormones

Answer 7

–PTH made, stored and secreted by chief cells of PTG–effects are to INCREASE Ca, DECREASE P (direct–bone, renal; indirect–GI)BONE: Ca, P resorption from increased osteoclastic activityRENAL: decrease excretion Ca, increase excretion P; activates vitamin D to calcitriol (1,25 dihydroxycholecalceferol)GI: calcitriol increases Ca and P absorption (INDIRECT)

Question 8

most physiologic form of calcium in the body

Answer 8

ionized Ca —most active

Question 9

where is calcitonin from and what is its function?

Answer 9

thyroid gland parafollicular cells (C cells)increases with increase Ca in order to LOWER Ca levelsdecreases bone resorptionNO effect on kidney, GI

Question 10

most functional thyroid tumors in cats are_____

Answer 10

BENIGN—adenoma, hyperplasia, goiterBILATERAL 70-90%one study said up to 25% could be carcinoma (70% metastatic rate)

Question 11

prevalence of coexisting renal disease in cats with hyperthyroidism

Answer 11

40%may need pretreatment with methimazole and recheck blood work to see if hyperthyroidism was masking underlying renal disease

Question 12

percentage of hyperthyroid cats that have hypokalemia

Answer 12

30%

Question 13

screening test for hyperthyroid cats

Answer 13

–PALPATE (90% have nodule)–total T4–elevated in 90% cats with hyperthyroidism–other tests: free T4, TSH stimulation test, T 3 suppression test–scintigraphy: confirms and localizes (technetium 99m)-not affected by methimazole tx bc radio nucleotide gets trap it is a not a function; will normally highlight thyroid, salivary glands, and gastric mucosa but intensity will be greater in thyroid

Question 14

considerations for anesthesia of a hyperthyroid cat

Answer 14

–avoid drugs that potentiate tachycardia/arrhythmias (ketamine, atropine)–beta antagonist if needed–supplement K if needed–ensure no previous renal insufficiency (pretreat with methimazole 2-3 weeks before sx)

Question 15

methods of thyroidectomy

Answer 15

–intracapsular–rate of recurrence is high, but preserves extra capsular PTG–modified intracapsular–extracapsular–no attempt to save PTG (may lead to hypoPTH)–modified extracapsular

Question 16

what is parathyroid autotransplantation

Answer 16

–left small or minced into small pieces–transplanted into a small incision on sternothyroideus/sternohyoideus muscle, then the muscle is closed–revascularized and functional in 7-21 days (need to treat for hypocalcemia in the meantime!)

Question 17

complications of thyroidectomy

Answer 17

–hemorrhage–dyspnea–laryngeal paralysis–megaesophagus (if both vagus injured)–horners–hypothyroidism (rare in cats)–hypoparathyroidism–hypocalcemia–recurrence of dz (hyperthyroidism or carcinoma)

Question 18

most serious complication of bilateral thyroidectomy

Answer 18

hypoPTH and resultant hypoCacats with ectopic PTH (up to 50%) is not enough to maintain normocalcemia78% dogs developed hypoCa with bilateral thyroidectomy/parathyroidectomy for carcinoma

Question 19

clinical signs of hypoCa

Answer 19

–restlessness–muscle twitching–facial pruritis–panting–tetany

Question 20

treatment for acute hypoCa

Answer 20

–Calcium gluconate 1 ml/kg IV slow with ECG or as a CRI in fluids–maintenance therapy with oral vitamin D and calcium; active form of vitamin D (calcitriol) can also be given orally hypoCa should resolve over 21 days, start taper over 8-16 weeks, maintain calcium in low normal range

Question 21

recurrence rate of hyperthyroidism in cats following bilateral thyroidectomy

Answer 21

10%

Question 22

what is the treatment of choice for hyperthyroid cats

Answer 22

radioactive iodine I-131permanent tx, make sure kidneys work(may need higher I 131 to treat carcinomas)

Question 23

behavior of canine thyroid tumors

Answer 23

90% detected clinically are malignant (papillary, follicular, compact, or anaplastic)40% have detectable mets at time of diagnosismost are nonfunctional (10% functional–hyperthyroid: almost always associated with malignancy)

Question 24

diagnostic approach for canine thyroid tumor

Answer 24

–PE (palpate cervical neck well)–cbc. chem. UA–coagulation panel–thyroid panel (<10% are functional but highly SP for malignancy)–thoracic imaging –cervical US +/- aspirate cytology (not often diagnostic) +/- biopsy (RISK HEMORRHAGE)–CT/MRI if indicated–scintigraphy if indicated

Question 25

prognosis/MST of thyroid carcinoma in dogs following surgical removal and prognostic factors

Answer 25

DEPENDS ON MOBILITY *, SIZE, STAGEMST 3 yr if freely movableMST 6-12 months if invasive

Question 26

metastasis and thyroid carcinoma

Answer 26

tumor size and bilateral disease are important factors< 23 cm cubed 15% met> 23-100 cm cubed 75% met> 100 cm cubed 100% metbilateral are 16x more likely to met

Question 27

treatment of choice for thyroid tumors that are nonresectable or incompletely excised

Answer 27

radioactive iodine, I-131MST with mets 365 dayMST with local disease 840 days

Question 28

what is euthyroid sick syndrome

Answer 28

decrease in thyroid tT4 concentration secondary to illness

Question 29

systemic effects of hypothyroidism on surgical patients

Answer 29

–cardiovascular effects: decr contraction, incr vascular R, decr CO–coagulation effects: decr factor VIII –wound healing effects: delay healing, incr risk infection (decreases humoral immune response)

Question 30

causes of hyperparathyroidism

Answer 30

1. primary : excessive production PTH from chief cells of PTG (adenoma 95%, solitary 50-90%): KEESHOUND (50x)2. secondary: renal or nutritional

Question 31

pathophysiology of primary hyperPTH

Answer 31

1. skeletal effects (fibrous osteodystrophy) from excessive calcium resorption from bone2. renal effects: Ca resorption eventually decreases renal function (Ca xP product dystrophic mineralization and vasoconstriction to decr renal blood flow)–>eventually causes hypercalciuresis: stones, UTI, PU/PD inability to respond to ADH and diabetes insipidus

Question 32

causes of hypercalcemia

Answer 32

G–granulomatous dzO–osteolytic diseases (OSA, osteomyelitis)S—spuriousH–hyperparathyroidism (primary)D–vitamin D toxicosis (rodenticide toxicity)A–Addisons (hypoadrenocorticism)R–renal secondary hyperPTH; renal failureN–neoplasia (LSA, AGASACA, MM, carcinomas), nutritional secondary hyperPTHI–iatrogenic, idiopathicT–trauma, hyperThermia

Question 33

expected PTH and Ca for primary hypoparathyroidism

Answer 33

low PTHlow Ca

Question 34

expected PTH and Ca for primary hyperPTH

Answer 34

hi or normal PTH (70% may be normal but still abN to see any PTH in the face of hyper Ca)hi Ca (increased ionized Ca)

Question 35

expected PTH and Ca for renal failure

Answer 35

hi or normal PTH (renal secondary hyperPTH)normal to hi Ca (total increased but not ionized)AZOTEMIC, hi P

Question 36

expected PTH and Ca for malignancy

Answer 36

low PTHhi Cahi parathyroid hormone related peptide

Question 37

preoperative mgmt of a hypercalcemic patient

Answer 37

1. fluid diuresis– NaCl2. loop diuretic—furosemide (watch K loss, may need to supplement)3. Calcitonin4. bisphosphonates5. GCC

Question 38

intraoperative detection of abN parathyroid glands

Answer 38

–methylene blue (heinz body anemia, ARF)–unilateral thyroparathyroidectomy and histopath–guillotine area found on US (partial thyroidectomy in the area of suspected abN PTG)

Question 39

re-testing PTH concentrations post op

Answer 39

if decreased by < 50% residual tissue likelyif decreased > 50% likely that all abN tissue removed

Question 40

how many PTG can safely be removed

Answer 40

3if all 4 removed likely need permanent Ca/Vit supplementation in dogs (unlike cats that have ectopic tissue)

Question 41

monitoring post op hyperPTH patient

Answer 41

–monitor Ca (total or ionized) 1-2 times a day for 5-7 days–calcitriol supplement–+/- oral Ca supplementGOAL: low normal calcium levels to stimulate other glands to work (total 8 mg/dL, ionized 0.8mmol/L)Gradual taper over 2-4 months; check calcium level prior to taper

Question 42

what group of hyperparathyroid patients have the greatest risk of developing post op hypocalcemia

Answer 42

patients with total serum calcium >14 mg/dl or has more than one PTG mass and potentially longer duration of hyperCavitamin D/calcitriol can be started pre-op and continued post op +/- oral calcium supplementation

Question 43

% of dogs developing clinically significant hypoCa post op

Answer 43

33% early as 12 hr or as late as 20 days

Question 44

resolution of hyperCa in post op hyperPTH patients

Answer 44

94% resolve 1 week post op

Question 45

recurrence of hyperCa and hyperPTH

Answer 45

8% within months to yearsKeeshounds

Question 46

alternative therapies to surgical removal of the PTG

Answer 46

–US guided intralesional ethanol ablation (caustic)–US guided heat ablation