Page 312 - Problem-Based Feline Medicine

304 PART 6 CAT WITH WEIGHT LOSS OR CHRONIC ILLNESS

Careful physical examination is essential for diag- exposure to allergens), genetic mutation, abnormal
nosis. Careful palpation of the ventral cervical region immune and/or hormonal responses.
is required to detect thyroid mass(es). Thorough ● 70% of the cats have both thyroid glands
abdominal palpation is essential to detect anterior affected.
abdominal pain (pancreatitis, hepatopathy), liver
1% of cases result from mild to moderately malig-
enlargement (diabetes-associated hepatopathy, hyper-
nant thyroid carcinoma.
adrenocorticism, lymphocytic cholangiohepatitis),
thickened bowel loops (inflammatory bowel disease, GIT signs may result from polyphagia, malabsorption
alimentary lymphosarcoma), mesenteric lym- or intestinal hypermotility.
phadenopathy (alimentary lymphosarcoma, occasion-
Polyuria/polydipsia may result from diuretic effects of
ally eosinophilic or suppurative inflammatory bowel
T4, increased renal blood flow, associated renal insuffi-
disease), ascites (lymphocytic cholangiohepatitis, pro-
ciency or compulsive polydipsia.
tein-losing nephropathy) or an enlarged uterus (late
pregnancy). General physical examination is impor- Cardiac effects result from a high output state, induced, in
tant to detect mild generalized lymphadenopathy part, by a demand for increased tissue perfusion to meet
(lymphosarcoma, lymphocytic cholangiohepatitis), an the needs of increased tissue metabolism. Cardiovascular
ill-kept coat (hyperthyroidism), a greasy coat (exocrine changes include left ventricular hypertrophy, left atrial
pancreatic insufficiency), alopecia and thin skin and ventricular dilation, increased myocardial contractil-
(hyperadrenocorticism), subcutaneous edema (pro- ity, and decreased peripheral vascular resistance. Other
tein-losing nephropathy), or extremities that appear contributors are the direct effect of thyroid hormones on
disproportionately enlarged (acromegaly). cardiac muscle and the nervous system.
Associated cardiac hypertrophy may cause congestive
DISEASES CAUSING SIGNS OF A THIN heart failure with tachycardia, a gallop rhythm, systolic
CAT WITH A GOOD APPETITE murmurs, dyspnea, apathy, hindlimb weakness due to
aortic thromboemboli or collapse.
HYPERTHYROIDISM*** Associated hypertension may be seen as ocular hemor-
rhage, or may cause clinical signs associated with cere-
Classical signs brovascular accidents, dementia and/or renal failure.
● Older cats (usually > 8 years). ● Up to 85% of cats with hyperthyroidism may develop
● Progressive weight loss, often with a systemic hypertension, either initially or even some
ravenous appetite. time after apparently successful treatment.
● May also show restlessness, a lack of
grooming, vomiting ± diarrhea, ± Clinical signs
polyuria/polydipsia.
Hyperthyroidism is the most common endocrinopa-
thy in cats; affecting ~1 in 300 pet cats.
Pathogenesis
It is seen mainly in older cats (>8 years of age); it is
99% of cases of hyperthyroidism result from benign occasionally seen in cats as young as 4 years, and has
nodular hyperplasia/adenoma. even been documented in an 8-month-old kitten.
● Disease results from autonomous secretion of thyrox-
There is no sex or breed predisposition, but Siamese
ine (T4) and triiodothyroxinine (T3). Negative feed-
cats appear to be under-represented.
back on the pituitary suppresses release of thyroid-
stimulating hormone (TSH) and normal thyroid Most cats have a history of weight loss and polyphagia.
tissue atrophies.
Weight loss usually occurs over several months.
● Cause is unknown but may involve diet (iodine
content, frequent changes, food additives), environ- 10–20% of cats will present with signs of inappetence
mental causes (in cat litter, toxins, pollution, with weight loss.