Page 331 - Problem-Based Feline Medicine

17 – THE CAT WITH WEIGHT LOSS AND A GOOD APPETITE 323

● They therefore develop polyuria, polydipsia and ● Ultrasonography and, where available, computed
polyphagia. tomography (CT) or magnetic resonance imaging
● They may either gain or lose weight. (MRI) can also be used to detect organomegaly. CT
and MRI may be used to determine the location and
While all organs undergo growth and hypertrophy,
extent of the tumor within the brain.
hepatomegaly and renomegaly are the easiest to detect
on palpation. Enlargement of the abdominal organs
Differential diagnosis
often results in a pot-bellied appearance.
Organ enlargement may lead to organ failure. The clin- Differential diagnoses include most of the other causes
ical signs will therefore reflect the particular organ sys- of weight loss with a good appetite. However, since all
tems that have been affected; e.g. cardiac hypertrophy cats with acromegaly develop diabetes with polyuria
and eventual congestive heart failure, liver failure and polydipsia, other causes of diabetes, hypera-
and/or kidney failure. drenocorticism, hyperthyroidism and renal insuffi-
ciency are the most important differentials.
Concurrent hypertension may result in clinical signs,
typically ocular hemorrhages, sudden blindness and/or
Treatment
neurological signs.
Acromegaly can be treated three ways; surgery,
Only rarely do neurological signs result from the pitu-
external-beam radiotherapy or medically.
itary tumor compressing and invading the hypothalmus.
● Surgical excision of the growth hormone-secret-
ing tumor is usually a rapid and effective treatment
Diagnosis for affected humans. However, the procedure has
Acromegaly should be considered in any large-sized rarely been performed in cats, and mapping of the
cat which develops insulin-resistant or unstable tumor is essential prior to considering surgery.
diabetes. ● In humans, external-beam radiotherapy is often
● Hyperglycemia and glycosuria will be present, but effective, although clinical improvement may be
ketosis is rare. slow to develop. The few cats that have been treated
● Affected cats may also show azotemia, hypercho- in this way have shown variable results. Treatment
lesterolemia, hyperphosphatemia, hyperproteine- requires repeated anesthetics and suitable facilities
mia, erythrocytosis and mildly raised liver are limited.
enzymes. ● Although they require frequent administration and
usually cause side-effects, somatostatin analogs
Comparing the cat to a previous photograph of itself
(e.g. octreotide) and dopamine agonists (e.g.
can be helpful in confirming the disproportionate
bromocriptine) are sometimes used in the treatment
enlargement and thickening of its head.
of humans with acromegaly. Unfortunately, limited
A definitive diagnosis can be made by measuring trials with octreotide in acromegalic cats have not
growth hormone levels (where available) or insulin- been promising, and dopamine agonists have not
like growth factor-1 (IGF-1) assay, which gives similar yet been evaluated in this species.
results. Unfortunately, the degree of elevation does not
Temporary management consists of trying to treat
always correlate with the clinical signs, and IGF-1 will
the diabetes and any other concurrent or related dis-
also be increased in most cats treated long-term with
eases (e.g. hypertension, heart failure, renal disease).
insulin.
● Control of the diabetes can usually be achieved by
The presence of acromegaly can be confirmed by eval- giving extremely high doses of exogenous insulin
uating the growth hormone response to a glucose (20–130 IU/day), sometimes in various combina-
suppression test. tions of short-, intermediate- or long-acting insulin.
Other tests can be used to gain supportive evidence. However, because the severity of the insulin resist-
● Radiography may show organomegaly, increased ance can fluctuate, the dose should not exceed
interdental spaces, hyperostosis of the skull and/or 12–15 IU/injection so the risk of iatrogenic hypo-
degenerative arthritis. glycemia is reduced.