FELINE HYPERTHYROIDISM Flashcards by evans monamati

LESIONS FOR FELINE HYPERTHYROIDISM

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

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CUASE FOR FRLINE HYPERTHYROIDISM

UNKNOWN

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SIGN. FOR FELINE HYPERTHYROIDISM

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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CS FOR FELINE HYPERTHYROIDISM

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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MOST COMMON CS OF HYPERTHYROIDISM

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

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CAUSES OF VOMITING IN A HYPERTHYROID CAT

Direct stimulation of CRTZ
Gastric distension / overeating
Increased GI motility

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CAUSES OF DIARRHOEAR IN A HYPERTHYROID CAT

Increased GI motility
Gastrointestinal malabsorption
- Voluminous Stool
- Steatorrhea
- Possible in pancreatic enzymes

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CAUSES OF PU/PD IN FELINE HYPERTHYROIDISM

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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DESCRIBE ALTERED BEHAVIOUR FOUND IN CATS WITH HYPERTHYROIDIMS

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

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DESCRIBE APATHIC FORM OF FELINE HYPERTHYROIDISM

< 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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PHYSICAL EXAM FINDINGS IN A CAT WITH HYPERTHYROIDISM

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

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

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chemistry findings for hyperthyroid cat

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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test for feline hyperthyroidism

Serum total T4
Serum free T4 (equilibrium dialysis)
T3 suppression test

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very reliable screening test for hyperthyroidism

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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serum free t4

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)


imaging findings for feline hyperthyroidism

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

Advantages of 99mTcO4 scintigraphy

Can identify bilateral versus unilateral disease
Can identify ectopic disease
Can identify metastatic dz

3 possible tx for hyperthyroidism

Drugs: Methimazole (Tapazole)
Surgery: Thyroidectomy
Radiotherapy: Radioactive iodine (131I)
- it replaced sx

advantage of methimazole tx

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)

adverse effects of methimazole

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)

advantages of thyrodectomy

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

complications and disadvantages of thyrodectomy

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)

effectiveness of radioactive iodine

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

Complications of Hyperthyroidism and the kidneys

* 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

complications of hyperthyroidism and hypertension

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)

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

thyroid storm These cats may become aggressive and/or hysterical with handling

tx for thyroid storm

* 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

px for feline hyperthyroidism

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

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FELINE HYPERTHYROIDISM Flashcards

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