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sam dr green > FELINE HYPERTHYROIDISM > Flashcards

FELINE HYPERTHYROIDISM Flashcards

1
Q

LESIONS FOR FELINE HYPERTHYROIDISM

A
  • Thyroid adenoma or adenomatous hyperplasia ≥ 97% cases
    • 70% bilateral; 30% unilateral
  • Adenocarcinoma is rare (≤ 3% of cases)
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2
Q

CUASE FOR FRLINE HYPERTHYROIDISM

A

UNKNOWN

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3
Q

SIGN. FOR FELINE HYPERTHYROIDISM

A
  • No breed predisposition
    • Himalayan and Siamese may have decreased risk
  • No sex predilection
  • Older cats
    • 4 to 22 years (mean -13 years)
    • >95% are > 8 years of age at diagnosis
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4
Q

CS FOR FELINE HYPERTHYROIDISM

A
  • Weight loss (> 90%)
  • Polyphagia (60%)
  • Polydipsia and polyuria (45-50%)
  • Altered behavior (40%)
  • Gastrointestinal signs (40%)
  • Vomiting (usually), diarrhea, voluminous feces
  • Heat intolerance (5%)
  • Panting (normally rare in cats) may occur
  • Hair Loss
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5
Q

MOST COMMON CS OF HYPERTHYROIDISM

A
  • Weight Loss with Polyphagia
  • Most common signs in affected cats
    • Often mild but can be severe
    • Both can worsen gradually
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6
Q

CAUSES OF VOMITING IN A HYPERTHYROID CAT

A
  • Direct stimulation of CRTZ
  • Gastric distension / overeating
  • Increased GI motility
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7
Q

CAUSES OF DIARRHOEAR IN A HYPERTHYROID CAT

A
  • Increased GI motility
  • Gastrointestinal malabsorption
    • Voluminous Stool
    • Steatorrhea
    • Possible in pancreatic enzymes
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8
Q

CAUSES OF PU/PD IN FELINE HYPERTHYROIDISM

A
  • Increased
    • Renal Blood Flow
    • Glomerular Filtration Rate
  • 2to cardiovascular changes
  • No Specific Renal Pathology due to T4
  • Low Urine Specific Gravity
    • 2to Loss of Medullary Concentration Gradient
    • May be primary psychogenic polydipsia
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9
Q

DESCRIBE ALTERED BEHAVIOUR FOUND IN CATS WITH HYPERTHYROIDIMS

A
  • Restless, irritable and aggressive
  • 2°to increased adrenergic tone (humans)
  • Seizures (rare)
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10
Q

DESCRIBE APATHIC FORM OF FELINE HYPERTHYROIDISM

A
  • < 10-15% of hyperthyroid cats
    • Lethargy
    • Decreased activity
    • Decreased appetite or anorexia
    • Weakness
  • May be associated with co-morbid systemic disorders (e.g. heart failure, chronic renal failure)
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11
Q

PHYSICAL EXAM FINDINGS IN A CAT WITH HYPERTHYROIDISM

A
  • Palpable enlargement of thyroid gland (91%)
    • Lentil to lima bean sized ……
    • Slips under your finger
  • Thin (71%)
  • Cardiovascular abnormalities
    • Tachycardia (48%)
    • Systolic murmur (41%)
    • Gallop (12%)
  • Hyperactivity (48%)
  • Skin problems and poor hair coat (35-40%)
    • Unkempt appearance
    • Decreased or increased grooming –matting or loss of hair
    • Excessive shedding
    • Increased rate of nail growth
    • Thin skin, loss of subcutaneous fat, decreased elasticity (makes assessment of hydration difficult
  • Hair Loss
    • Bilateral endocrine alopecia not generally seen
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12
Q

WHAT MAY U FIND WHEN DOING ABDOMINAL PALPATION OF A HYPERTHYROID CAT

A
  • Small kidneys (26%)
    • CKD may co-exist with hyperthyroidism complicating diagnosis and treatment (more later)
  • Mild hyperthermia (14%)
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13
Q

chemistry findings for hyperthyroid cat

A
  • Mild to moderate increase in liver enzyme activities (ALT, ALP, AST) (60-90%)
  • Azotemia (25%) indicates need to carefully evaluate renal function because ↑T4 increases RBF and GFR and these changes (and muscle wasting) decrease creatinine (i.e. renal function “looks better than it is”)
  • Mild hyperphosphatemia (10-30%) due possibly to increased bone turnover
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14
Q

test for feline hyperthyroidism

A
  • Serum total T4
  • Serum free T4 (equilibrium dialysis)
  • T3 suppression test
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15
Q

very reliable screening test for hyperthyroidism

A
  • serum total t4
  • Sensitivity –91%
  • 1-2 μg/dL: normal
  • 2-5 μg/dL: suspicious
  • > 5 μg/dL: supports Dx
  • Normal in ≤ 10% of affected cats
  • Daily fluctuations in early disease
  • Non-thyroidal illness
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16
Q

serum free t4

A
  • Serum free T4 by equilibrium dialysis (fT4)
  • More sensitive (but less specific) than total T4
  • Normal: 15-48 pmol/L
  • Can be checked if total T4 is normal (fT4 is less often affected by non-thyroidal illness)
17
Q

imaging findings for feline hyperthyroidism

A
  • Thoracic radiographs: Variable cardiomegaly (50%)
  • Echocardiography: +/-ventricular hypertrophy
  • Electrocardiography
  • Sinus tachycardia (40%)
  • Increased R wave > 1.0 mV (20%)
  • Abnormalities resolve with treatment
  • CHF can occur secondary to hyperthyroidism
18
Q

Advantages of 99mTcO4 scintigraphy

A
  • Can identify bilateral versus unilateral disease
  • Can identify ectopic disease
  • Can identify metastatic dz
19
Q

3 possible tx for hyperthyroidism

A
  • Drugs: Methimazole (Tapazole)
  • Surgery: Thyroidectomy
  • Radiotherapy: Radioactive iodine (131I)
    • it replaced sx
20
Q

advantage of methimazole tx

A
  • Reversibly inhibits thyroid peroxidase
  • n.b good to do methimazole challenge before giving iodine tx to check for renal dz
  • Thyroid nodule will not get smaller (may actually get bigger)
21
Q

adverse effects of methimazole

A
  • Mild adverse effects in 10-15% of treated cats
  • Anorexia, vomiting, lethargy
  • Less common (potentially more serious) adverse effects
  • Cutaneous excoriations (2-3%): often pre-auricular
  • Hematologic changes (3-9%): eosinophilia, neutropenia, lymphocytosis, thrombocytopenia
  • Increased liver enzymes (2%)
  • IMHA (< 1%, but up to 50% develop positive ANA test)
  • Platelet dysfunction (rare)
22
Q

advantages of thyrodectomy

A
  • Not commonly used (availability of radioactive iodine)
  • Advantages:
  • Potentially curative
  • Available in private practice
23
Q

complications and disadvantages of thyrodectomy

A

Irreversible
Damage to parathyroid blood supply: transient or permanent hypocalcemia postoperatively (usually within 2-5 days)
Poor anesthetic risk: control thyrotoxicosis first with methimazole
Risk of Horner’s syndrome if damage to vagosympathetic trunk
Risk of change in meow/purring if recurrent laryngeal nerve damaged
Recurrence or development of disease in contralateral lobe
Clinical hypothyroidism postoperatively (bilateral removal)

24
Q

effectiveness of radioactive iodine

A
  • 131I dose can be estimated by severity of clinical signs, size of thyroid nodule, and serum total T4 –most affected cats require 3 to 5 mCi (larger doses for neoplasia)
  • Serum T4 decreases to normal over several days to weeks after treatment
  • 95% of treated cats are euthyroid within 3 months after a single treatment
25
Q

Complications of Hyperthyroidism and the kidneys

A
  • Hyperthyroidism increases RBF and GFR which decreases BUN and creatinine and makes the kidneys “look better than they are”
  • CRF is a non-thyroidal illness that can lower serum T4 and make the diagnosis difficult
  • Renal function may worsen after treatment when RBF and GFR return to pre-treatment levels
26
Q

complications of hyperthyroidism and hypertension

A

Hypertension doesn’t necessarily resolve with treatment of hyperthyroidism
May require treatment with a calcium channel blocker (amlodipine 0.625 to 1.25 mg/day)

27
Q

a cat prsents with Severe tachycardia, open-mouthed breathing, hypoxia, and a “panic-attack” mental status

A

thyroid storm

These cats may become aggressive and/or hysterical with handling

28
Q

tx for thyroid storm

A
  • Reduce stress!
    • Too much handling or restraint (blood draws, catheter placement, radiographs) will exacerbate catecholamine release, and can precipitate hypertensive event or a fatal cardiac arrhythmia
  • Oxygen and cage rest (oxygen cage, NOT oxygen mask)
  • Start a beta-blocking agent ASAP
    • Propranolol is drug of choice
    • Dose: 1 -2 mg/kg BID –TID
  • Start methimazole
29
Q

px for feline hyperthyroidism

A

Very good
Average survival is 2 years
Often die of some other geriatric disease

30
Q
A

sam dr green (10 decks)

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