Page 244 - Problem-Based Feline Medicine

236 PART 4 CAT WITH URINARY TRACT SIGNS

● It occurs mainly from erythropoietin deficiency, but Pathogenesis
other factors contribute, such as decreased red cell
Most diabetic cats appear to have type 2 diabetes mel-
lifespan.
litus, previously called adult-onset diabetes or non-
Proteinuria is typically mild to moderate (1.5–2 times insulin-dependent diabetes.
increase in protein excretion occurs). ● Type 2 diabetes is characterized by decreased
insulin secretion, insulin resistance and amyloid
Radiographs of kidneys may show small irregular kid-
deposition in the pancreatic islets.
neys; size may be normal or increased in some cats
especially if renal failure is due to amyloid, neoplasia Risk factors include old age, male gender, obesity,
or polycystic kidneys. physical inactivity, confinement indoors, Burmese breed
(in Australia, New Zealand and UK), and repeated or
Ultrasound examination frequently shows small
long-acting steroid or megestrol acetate administration.
hyperechoic kidneys.
At diagnosis, endogenous insulin secretion is usually
very low.
Differential diagnoses ● This is probably because of the combined effects of:
– Impaired insulin secretion associated with the
Pre-renal azotemia. This occurs secondary to dehy-
beta cell defect causing type 2 diabetes.
dration or circulatory collapse; azotemia results from
– Amyloid deposition in the islets which replaces
reduced renal blood flow; typically urine specific
beta cells.
gravity is ≥ 1.035, in contrast to renal failure where SG
– Suppression of insulin secretion by glucose toxicity.
is < 1.035.
Glucose toxicity is defined as suppression of insulin
Pre-renal azotemia together with concomitant pri-
secretion by persistently (> 24 h duration) high
mary disease that affects renal concentrating ability
blood glucose.
can mimic renal failure, e.g. a dehydrated cat with central
● Suppression of insulin secretion by glucose toxicity
or nephrogenic diabetes insipidus may have azotemia
is initially functional and reversible, later it
with a urine specific gravity < 1.035.
results in structural changes in beta cells. With
time (weeks) changes become irreversible, and
Treatment beta cells are lost.
Some cats (5–20%) have other specific types of dia-
See main reference on page 336 for details.
betes. Their diabetes results from another disease
Correct dehydration, reduce uremia, and improve qual- process causing decreased insulin secretion or impaired
ity of life. insulin action (insulin resistance).
● Pancreatic neoplasia is a significant cause of dia-
betes in cats referred to specialists, accounting for
as many as 18% of cases recorded at referral insti-
DIABETES MELLITUS***
tutions in USA.
● Pancreatitis is commonly associated with feline
Classical signs
diabetes (50% of diabetic cats have pancreatitis
● Older than 6 years of age, most > 8 years of lesions at necropsy).
age. – In most cats, pancreatitis is not severe enough to
● Moderate to marked PU/PD, usually of 2–8 cause diabetes alone, but probably contributes to
weeks duration. loss of beta cells.
● Weight loss, but may be normal weight, ● Hyperadrenocorticism and growth hormone-
obese or underweight. producing tumors (acromegaly) are rare causes of
● Polyphagia or inappetence. other specific types of diabetes associated with
insulin resistance.