Page 263 - Problem-Based Feline Medicine

15 – THE CAT WITH POLYURIA AND POLYDIPSIA 255

the hormone. These anabolic actions are mediated by Diagnosis
insulin-like growth factor-1, a growth factor synthe-
Diagnosis is based on clinical signs and increased
sized in the liver and also locally in the growth plate of
plasma concentrations of insulin-like growth factor-
bones. The effects of excess growth hormone are
1 (> 1200 U/L).
chronic and insidious.
Growth hormone concentrations can be measured
Acute catabolic actions of growth hormones result in
with an assay developed for dogs, available at some
fat breakdown (lipolysis) and glycolysis. Hyperglycemia
research laboratories. Demonstration of persistently
results from increased gluconeogenesis in the liver and
elevated GH concentrations, which do not increase
decreased glucose uptake into tissues as a result of
with stimulation from GHRH or clonidine, support the
insulin resistance. Long term, the marked insulin resist-
diagnosis, but is not readily available to most practi-
ance results in diabetes mellitus.
tioners.
Insulin resistance may be extreme with insulin doses
A pituitary mass on CT or MRI scan supports the
between 20–130 U/day required to control blood glucose.
diagnosis, and is useful for monitoring response to irra-
Clinical signs diation therapy.
Cats are typically middle aged to elderly, with a pre-
dominance of males. Differential diagnosis
All cats reported have diabetes mellitus, and in most Other causes of poorly controlled insulin-resistant
cats, their diabetes is poorly controlled and insulin- diabetes need to be distinguished from acromegaly.
resistant. Normal doses of insulin produce no or mini- When insulin resistance is extreme and insulin dose
mal decrease in glucose concentration, and in many exceeds 20–30 U/cat/injection without causing hypo-
cats, very large doses of insulin are required to produce glycemia, the likely cause is acromegaly. Most other
an acceptable glucose-lowering effect. causes of insulin resistance produce less extreme
insulin resistance and very high doses of insulin pro-
Polyphagia, polyuria and polydipsia are associated
duce severe hypoglycemia.
with poorly controlled diabetes.
Hyperadrenocorticism causes poorly controlled
Typically, there is weight gain despite poorly con-
insulin-resistant diabetes. Typically, insulin doses
trolled diabetes, although sometimes weight loss is
required to control hyperglycemia are much lower
present.
than for acromegaly. In contrast to acromegaly, cats
A large, blocky or coarse body is typical, and cats with hyperadrenocorticism have weight loss. Other
often have coarse facial features. General coarsening of signs suggestive of hyperadrenocorticism are a poor
body type is evident when the cat is compared to pic- hair coat and fragile skin, which may tear with
tures taken several years before. restraint for blood sampling or insulin injection. Many
have a potbelly (may also be present in acromegaly)
Acromegalic cats often have thickened enlarged
and hepatomegaly.
tongues, sometimes widely spaced teeth and a thick-
ened soft palate. Displacement of lower canine teeth Other causes of apparent insulin resistance such as
forward (prognathia inferior) may occur. excessive insulin dose resulting in rebound hyper-
glycaemia or use of an insulin of insufficient dura-
Cardiomegaly is often evident on radiographs and
tion of action result in poorly controlled diabetes, but
occasionally congestive heart failure occurs resulting in
clinical signs of acromegaly are absent.
dyspnea.
Degenerative arthritis may occur resulting in stiffness
on rising and walking. Periosteal reaction is evident Treatment
around the joints on radiographs.
Cobalt radiation has been used successfully, and may
Renal failure occurs in some cats. result in resolution of the diabetes in some cats.