Page 75 - Clinical Small Animal Internal Medicine
P. 75
43
VetBooks.ir
6
Feline Acromegaly
David S. Bruyette, DVM, DACVIM (SAIM)
Anivive Lifesciences, Long Beach, CA, USA
Etiology/Pathophysiology examined the incidence of acromegaly in the diabetic cat
and Epidemiology population. A recent study in the United Kingdom meas
ured IGF‐1 levels in variably controlled diabetic cats. Of
Feline acromegaly is a disease characterized by excessive the 184 cases, 59 (32%) had markedly increased IGF‐1
growth hormone secretion leading to a wide array of concentrations. Eighteen of these 59 cats underwent pitu
clinical signs caused by the hormones’ effects on multi itary imaging, confirming a diagnosis of acromegaly in
ple organ systems. These effects can be divided into two 17/18 (94%). A second study examined 225 cats with vari
major classes. The first are the catabolic actions of ably controlled diabetes and 40 (17.8 %) had markedly
growth hormone that include insulin antagonism, lipoly high IGF‐1 concentrations. In the largest study to date, of
sis, and gluconeogenesis with the net effect of promoting 1222 cats with diabetes, 323 (26.4 %) had IGF‐1 suggesting
hyperglycemia. The second are the slow anabolic (or acromegaly and 90% had a pituitary mass upon imaging
hypertrophic) effects of growth hormone, which are (CT or MRI). This suggests that 18–32% of diabetic cats
mediated by insulin‐like growth factors. Growth hor may have concurrent acromegaly and acromegaly may be
mone stimulates production of insulin‐like growth fac one of the most important predisposing factors to feline
tors in several different tissues. Insulin‐like growth diabetes through the induction of insulin resistance.
factor‐1 (IGF‐1), which is produced in the liver, is thought
to be the key factor that facilitates the anabolic effects of
growth hormone that are responsible for the characte Etiology
ristic appearance of acromegalic people, dogs, and cats. Acromegaly in humans is usually sporadic, but up to 20% of
Growth hormone is produced in the pars distalis (ante familial isolated pituitary adenomas are caused by germline
rior pituitary), specifically by acidophilic cells, called sequence variants of the aryl‐hydrocarbon‐receptor inter
somatotrophs. The release of growth hormone is regu acting protein (AIP) gene. The AIP gene is associated with
lated by many factors, the most important of which is xenobiotic metabolizing enzymes and endocrine disrupt
growth hormone‐releasing hormone (GHRH) produced ing chemicals in the environment, such as bisphenol A and
by the hypothalamus. Recently, another hormone, ghrelin, PBDEs, have been linked to both feline acromegaly and
has also been identified as a potent stimulator of growth hyperthyroidism. Feline acromegaly has similarities to
hormone release. Ghrelin is produced by the stomach and human acromegalic families with AIP mutations. A recent
released following ingestion of a meal. study sequenced the feline AIP gene, to identify sequence
Release of growth hormone is inhibited by the hypo variants and compare the AIP gene sequence between
thalamic hormone somatostatin as well as by growth feline acromegalic and control cats, and in acromegalic sib
hormone and IGF‐1 via negative feedback. Feline acro lings. A single nonsynonymous single‐nucleotide polymor
megaly is typically the result of a functional adenoma of phism (SNP) was identified in exon 1 (AIP:c.9T > G) of two
the pituitary that releases growth hormone despite nega acromegalic cats and none of the control cats, as well as
tive feedback resulting in excessive growth hormone both members of one sibling pair. The region of this SNP is
production and release. considered essential for the interaction of the AIP protein
Feline acromegaly, thought to be an uncommon disease with its receptor. This sequence variant has not previously
until recently, is likely underdiagnosed. Three studies have been reported in humans. Two additional synonymous
Clinical Small Animal Internal Medicine Volume I, First Edition. Edited by David S. Bruyette.
© 2020 John Wiley & Sons, Inc. Published 2020 by John Wiley & Sons, Inc.
Companion website: www.wiley.com/go/bruyette/clinical
