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!Small Animal Medicine > Hyperthyroidism > Flashcards

Hyperthyroidism Flashcards

1
Q

Thyroid gland physiology

A

Follicular cells (thyrocytes)
Lumen filled with colloid
Parafollicular (C) cells (secrete calcitonin)

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2
Q

Production of the thyroid hormone

A

Na+/I- symporter transports Na ions across membrane with iodide ion (iodide trapping) → TSH released form pituitary and binds to TSH receptor stimulating the endocytosis of the colloid → Endocytosed vesicles fused with lysosomes of the follicular cell → thyroid hormones released

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3
Q

Thyroid hormones released

A

r-T3 (biologically inactive)
Triiodothyronine/ T3 (active)
Thyroxine (T4)

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4
Q

Function of thyroid glands

A

Catabolic on muscle and adipose tissue, stimulate erythropoiesis
Needed for normal skeletal/ neurologic maturation and regulate cholesterol synthesis/ degradation

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5
Q

Hyperthyroidism in cats

A

Most common endocrine dz of cats caused by neoplasia and hyperplasia (most benign)

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6
Q

Hyperplasia causing hyperthyroidism in cats

A

Adenomatous hyperplasia on one or both lobes
Nodules formed from <1 mm to >3mm

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7
Q

Hyperthyroidism in dogs

A

Rare
Thyroid carcinoma (10-20% functional)

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8
Q

CS of hyperthyroidism

A

WL with polyphagia
Hyperactivity and ↑ vocalization
PU/PD, V/D
Sudden blindness, heart murmur

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9
Q

Signalment of hyperthyroidism

A

Middle-aged to old cats (4-22y)

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10
Q

PE for a cat with hyperthyroidism

A

Palpate for thyroid nodule/ slip (not all will have)
Poor BCS, dull hair coat, dehydration, hyperactivity, tachycardia

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11
Q

Clin path associated with hyperthyroidism

A

↑ ALT, ALKP (return to normal @ euthyroid)

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12
Q

Dx hyperthyroidism

A

Palpation of enlarged node
Free T4 equilibirum dialysis: ↑ T4

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13
Q

Subclinical hyperthyroidism

A

Thyroid slip with no CS or consistent lab abnormalities (not relying on TSH mechanism)
Low TSH, normal T4 and fT4

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14
Q

Hyperthyroidism and Chr. Kidney Dz

A

Concurrent renal dysfunction common in untx cats
↓ GFR, ↑ BUN and creatinine, azotemia

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15
Q

Contribution of hyperthyroidism to CKD

A

Untx hyperthyroid cats develop proteinuria
High levels of retinol binding protein (tubular dysfunction and damage)
High urinary N-acetyl-beta-D-glucosaminidase

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16
Q

CKD in hyperthyroid cats

A

GFR falls once treated (1m)
Medical management b4 definitive tx: low dose methimazole

17
Q

Other dx for hyperthyroid

A

BP (hypertension)
ECG: Tall R waves
Thoracic rads: Cardiomegaly, pleural effusion
Echo: HCM
Pertechnetate scan (nuclear medicine scan)

18
Q

Tx the cardiovascular effects of hyperthyroid

A

Beta blockers (atenolol)
if tachycardic/ hypertensive

19
Q

Tx for hyperthyroidism

A

Methimazole: blocks thyroid hormone synthesis by stopping thyroid peroxidase
(reversible effects)

20
Q

Adverse effects of methimazole

A

GI most common
Blood dyscrasias (neutropenia and thrombocytopenia)
Facial excoriation
Hepatotoxicity (hep necrosis and degeneration)
Renal decompensation
Coagulation abnormalities
Acquired MG

21
Q

Monitoring methimazole therapy

A

CBC, Chem, UA and T4 @ 2-3w and 4-6w
T4 1.5-3.0 ug/dL

22
Q

Nutritional management of hyperthyroid

A

Dietary Hill’s y/d
A reduction of iodine as a substrate for thyroid hormone production

23
Q

Thyroidectomy

A

Unilateral or bilateral (usually both taken)
Extracapsular: high risk, cautery cr. thyroid artery
Inracapsular: recurrence, remove some capsule

24
Q

Complication of the thyroidectomy?

A

Secondary cardiomyopathy
Recurrent or incomplete removal
Hypoparathyroidism → post-op hypocalcemia

25
Q

Radioiodine therapy

A

Tx of choice if bilateral, ectopic thyroid carcinomas
Initial medical therapy trial to ensure renal stability
Isolated for 7-10d after tx

26
Q

I131 mechanism of action

A

Concentrated in thyroid gland where it will irradiate and destroy the hyperfunctioning tissue
Emits B-particles (travels short distances) and Y-radiation

27
Q

I131 adverse effects

A

Rare transient dysphagia and fever and voice change
Worsening renal dz
Hypothyroidism (with azotemia)

28
Q

I131 monitoring

A

T4 @ 4w and 3m post-tx

29
Q

Monitoring hyperthyroid prior to I131 tx

A

Thoracic rads within 30d of tx
CBC, Chemistry screen, diagnostic T4 by outside lab
UA with UPC

30
Q

After I131 tx

A

Patients released to owners according to strict federal regulations
Excrete small amounts of radioiodine release

!Small Animal Medicine (32 decks)

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