Page 780 - Small Animal Internal Medicine, 6th Edition

752 PART VI Endocrine Disorders

may also be found. Renal failure is a potential sequela of diabetic cats in which the poor control was not caused by
acromegaly and, if present, will be associated with azotemia, acromegaly and in cats with acromegaly that do not have
VetBooks.ir isosthenuria, and proteinuria. concurrent diabetes mellitus. In the nondiabetic cats, acro-
megaly is usually suspected based on the presence of a large
Diagnosis
abnormalities.
Clinical suspicion for acromegaly is based on the identifica- cat with prognathia inferior, organomegaly, and cardiac
tion of conformational alterations (e.g., increased body size, Interpretation of serum IGF-1 test results should always
large head, prognathia inferior, organomegaly) associated take into consideration the status of control of the diabetic
with acromegaly and a stable or progressive increase in body state, the presence and severity of insulin resistance, and the
weight in a cat with insulin-resistant diabetes mellitus. Mea- index of suspicion for acromegaly based on review of the
surement of serum IGF-1 concentrations provides further history, physical examination, and results of routine blood
evidence for the diagnosis of acromegaly. Measurement of and urine tests and diagnostic imaging. Identification of an
serum IGF-1 is commercially available (e.g., the Diagnostic increased serum IGF-1 concentration in a poorly controlled
Center for Population and Animal Health, Michigan State diabetic cat with insulin resistance and clinical features sug-
University, East Lansing, Mich; www.dcpah.msu.edu). Con- gestive of acromegaly supports the diagnosis and provides
centrations are usually increased in acromegalic cats, but justification for CT or MR imaging of the pituitary gland. A
values may be in the reference range in the early stages of pituitary mass documented by CT or MR scanning (see Fig.
the disease (Fig. 46.7). Repeat measurements performed 3 to 46.5) adds further evidence for the diagnosis and is indicated
6 months later usually reveal an increase in serum IGF-1 if whenever the client is considering radiation treatment. It is
acromegaly is present. This increase in serum IGF-1 typically usually necessary to administer a positive contrast agent for
coincides with development and growth of the pituitary visualization of a pituitary mass when CT or MR imaging is
somatotropic adenoma. Serum IGF-1 concentrations are used.
lower in newly diagnosed untreated diabetic cats, compared A definitive diagnosis of acromegaly requires documenta-
with healthy cats, and serum IGF-1 concentrations increase tion of an increased baseline serum GH concentration. Base-
after initiation of insulin treatment. Fortunately, most cats line serum GH concentration in cats with acromegaly
are diabetic and being treated with insulin at the time acro- typically exceeds 10 ng/mL (reference range varies with the
megaly is diagnosed. Increased serum IGF-1 concentrations laboratory but is typically < 7.2-7.9 ng/mL in cats). Unfortu-
have been identified in a small number of poorly controlled nately, a commercial GH assay is not currently available for
cats in the United States.

300
ACROMEGALY VERSUS
Serum insulin-like growth factor-l (nmol/L) 200 * a Hyperadrenocorticism and acromegaly are uncommon dis-
HYPERADRENOCORTICISM
250
orders that occur in older cats, have a strong association
with diabetes mellitus, can cause severe insulin resistance,
and are often caused by a functional pituitary macrotumor.
150
Clinical signs related to poorly controlled diabetes mellitus
are common in cats with hyperadrenocorticism and acro-
100
megaly. Additional clinical signs differ dramatically between
50
ing disease that results in progressive weight loss leading
*
to cachexia and dermal and epidermal atrophy causing
*
0
extremely fragile, thin, and easily torn and ulcerated skin
Healthy Well-controlled Poorly controlled Diabetics with the two disorders. Hyperadrenocorticism is a debilitat-
diabetics diabetics acromegaly (i.e., feline fragile skin syndrome). In contrast, conforma-
tional changes caused by the anabolic actions of chronic
FIG 46.7 IGF-1 secretion dominate the clinical picture in acromegaly,
Box plots of serum concentrations of insulin-like growth
factor 1 (IGF-1) in 38 healthy cats, 15 well-controlled most notably an increase in body size, prognathia inferior,
diabetic cats, 40 poorly controlled diabetic cats, and 19 and weight gain despite poorly regulated diabetes mellitus.
poorly controlled diabetic cats with acromegaly. For each Feline fragile skin syndrome does not occur with acromeg-
box plot, T-bars represent the main body of data, which in aly. With both disorders most of the abnormalities identified
most instances is equal to the range. Each box represents on routine blood and urine tests are caused by concurrent
the interquartile range (twenty-fifth to seventy-fifth percentile). poorly controlled diabetes mellitus. Abdominal ultrasound
The horizontal bar in each box is the median. Asterisks may reveal mild bilateral adrenomegaly with both disor-
represent outlying data points. a, P < 0.0001, compared
with healthy cats and well-controlled and poorly controlled ders. Ultimately, differentiation between the two diseases
diabetic cats. (From Berg RIM, et al.: Serum insulin-like is based on results of tests of the pituitary-adrenocortical
growth factor-I concentration in cats with diabetes mellitus axis (see Chapter 50) and serum GH and/or IGF-1
and acromegaly, J Vet Intern Med 21:892, 2007.) concentrations.