Page 445 - Problem-Based Feline Medicine

21 – THE YELLOW CAT OR CAT WITH ELEVATED LIVER ENZYMES 437

● Ultrasonography is useful in detecting involvement Weight loss, polyphagia and unkempt haircoat are com-
of multiple hepatic lobes and in obtaining a guided mon.
core biopsy of lesions.
Vomiting and small bowel diarrhea may be observed.
Definitive diagnosis requires histologic evaluation of
A reduced appetite is seen in about one in ten cats with
liver biopsy specimens.
hyperthyroidism.
Panting and respiratory distress are observed with con-
Differential diagnosis comitant cardiac disease.
It is important to distinguish benign from malignant Seen primarily in middle-aged and older cats.
hepatic tumors, as treatment and prognosis are widely
Physical examination is suggestive.
divergent. Differentiation may only be made by histo-
● Palpable thyroid gland enlargement is evident in
logic interpretation of hepatic biopsy specimens.
90% of cats if the examiner is experienced.
● Patchy alopecia/unkempt haircoat, overgrown toe
Treatment nails are often present.
● Reduced muscle mass; most cats are thin.
Surgical resection (lobectomy) of benign hepatocellu-
lar or biliary tumors is recommended. Cardiac auscultation may reveal cardiac disturbances.
● Tachycardia (>240 bpm), murmurs and/or a gallop
Chemotherapy is not useful for treatment of malignant
rhythm suggest cardiac manifestations of thyrotoxi-
neoplasia.
cosis.
Prognosis Diagnosis

The prognosis for cats with benign tumors after resection
Increased liver enzyme (ALT, ALP) activities are seen
is good. Most cats are disease free at least 1 year later.
in > 75% of hyperthyroid cats.
The prognosis for malignant neoplasia is poor.
Closely assess renal parameters (BUN, creatinine, uri-
nalysis) as concomitant renal disease may be present.
HYPERTHYROIDISM
Demonstration of elevated basal serum thyroxine (T )
4
concentration provides definitive diagnosis.
Classical signs
● Suspicious cats with a “borderline” T value should
4
● Rarely seen in cats < 8 years of age. be retested.
● Weight loss, polyphagia and unthrifty ● Increased free T may be observed in some cats
4
appearance predominate. with high normal total T concentrations.
4
● Polyuria/polydipsia +/- vomiting/diarrhea ● Alternatively, performance of a T suppression test
3
may be seen. may discriminate between normal and mildly
hyperthyroid cats.
See main reference, page 304 (The Cat With Weight
Perform thoracic radiography, electrocardiography
Loss and a Good Appetite).
(ECG), +/− echocardiography to rule out cardiac disease.
Clinical signs
Clinical signs result from overproduction/secretion of FELINE LEUKEMIA VIRUS
thyroid hormones. Malignant thyroid tumors are rare.
See page 424 under pre-hepatic causes for jaundice and
More than 70% of hyperthyroid cats have bilateral thy- page 432 for hepatic causes for jaundice (e.g. lympho-
roid adenomas or adenomatous hyperplasia. sarcoma).