Page 355 - Problem-Based Feline Medicine

18 – THE THIN, INAPPETENT CAT 347

As tachycardia (with or without cardiac failure) is often roidism) and methimazole (10–15 mg/day PO
present, cardiac disease should be placed high on the divided q 8–12 hours for 2–3 weeks, then 7.5–10
differential diagnosis list. mg/day PO divided q 12 hours to maintain euthy-
roidism) are the drugs of choice for both short-
For cats with polydipsia and polyuria in addition to
and long-term medical management of hyperthy-
inappetence and weight loss, the main differential diag-
roidism. Transdermally absorbed methimazole
noses would include chronic renal failure and diabetes
may be obtained from a compounding pharmacist,
mellitus.
and may be useful if the owners are unable to give
oral medication.
Treatment – Exact dosage should be adjusted on the basis of
basal total T concentrations.
Hyperthyroid cats may be treated by surgical thy- 4
– Failure of efficacy is usually due to poor com-
131
roidectomy or radioactive iodine ( I), which are
pliance.
curative, or alternatively the condition may be con-
– Adverse effects appear to be less common with
trolled using antithyroid therapy.
carbimazole than methimazole and usually occur
The ideal form of treatment for each case will depend in the first 3 months of therapy.
on a number of factors: – Transient vomiting, anorexia and lethargy have
● Age of the cat. been reported, and usually resolve without with-
● Presence of concurrent disease, particularly chronic drawal of the drug.
renal failure or cardiovascular disease. – Serious hematological adverse effects may
● Availability of appropriate nuclear medicine facilities. occur, and so routine monitoring is required.
● Owner’s wishes, including ability to medicate cat – Hepatopathy and self-induced facial excoriation
and cost. may rarely occur.
● Other medical therapies may be considered includ-
Cats with apathetic hyperthyroidism frequently
ing atenolol (to reduce the cardiac effects of hyper-
have concurrent disease, and it is essential that this
thyroidism), stable iodine (preoperatively to
is thoroughly investigated and considered prior to
reduce gland vascularity) and ipodate.
embarking on therapy.
● Cardiac disease may preclude safe anesthesia and Surgical thyroidectomy is curative when it is possi-
surgical thyroidectomy. ble to remove all abnormal thyroid tissue.
● Glomerular filtration rate declines with resolution ● Medical stabilization, ideally for 3 weeks pre-
of the hyperthyroid state. Therefore, any cat sus- operatively significantly reduces the anesthetic
pected of having underlying renal disease (azotemia, and surgical complications.
creatinine and urea concentrations in the upper part of ● The most common complication is post-operative
the reference range, or lack of urine-concentrating hypoparathyroidism, although Horner’s syndrome
ability) should be treated with antithyroid medication and laryngeal paralysis may also occur.
until it can be determined if induction of euthy-
Radioactive iodine therapy is the treatment of
roidism would have detrimental effects.
choice for most hyperthyroid cats when suitable
Medical therapy for hyperthyroidism is used in the facilities for treatment are available.
short term to stabilize a hyperthyroid cat prior to ● This is the treatment of choice for cats with hyper-
surgical thyroidectomy, as trial therapy assesses the thyroidism induced by thyroid carcinoma.
effect on renal function prior to curative treatment, ● Complications include the induction of permanent
or for long-term management if surgery or radioio- hypothyroidism and incomplete ablation requiring
dine therapy are not suitable. an additional treatment.
● Medical management merely blocks thyroid hor- ● The principal disadvantage is a period of isola-
mone synthesis and so requires continuous life-long tion is required to comply with local radiation
treatment. safety regulations. This makes treatment of inter-
● Carbimazole (5 mg PO q 8 hours for 2–3 weeks, current disease difficult or impossible during this
then 5 mg PO q 12 hours to maintain euthy- time.