Page 588 - Withrow and MacEwen's Small Animal Clinical Oncology, 6th Edition

566 PART IV Specific Malignancies in the Small Animal Patient

Adrenal-dependent hypercortisolism (ADH) refers to disease including both functional or nonfunctional adrenocortical tumors
of the adrenal cortex, including neoplasia, dysplasia, or hyperpla- and pheochromocytomas. 16,19–23 Thus ultrasound findings must
always be interpreted concurrently with clinical findings and
sia, and is discussed in the section on adrenal gland tumors.
VetBooks.ir Clinical Findings and Diagnostic Evaluation in endocrine test results. Abdominal CT is used less commonly than
ultrasonography to evaluate the adrenals, but CT findings may
Dogs also assist in the discrimination between PDH and ADH. 24,25
This technique also demonstrates overlap between adrenal volume
Most dogs with PDH are older than 9 years of age, and female in dogs with PDH and dogs with nonadrenal disease and also
dogs are slightly overrepresented. Breed predispositions have been confirms that dogs with PDH can have nodular adrenal lesions. 25
noted in dachshunds, terrier breeds, German shepherd dogs, and Although 80% to 85% of dogs with spontaneous HAC have
poodle breeds. The onset of canine Cushing’s syndrome is often PDH and the great majority of cases of PDH are the result of the
slow, and the signs can progress slowly. Affected dogs are often presence of a pituitary tumor, canine patients do not often show
not considered by their owners to be sick; they have a good appe- clinical signs directly referable to the local effects of the tumor.
tite and do not show signs such as vomiting, diarrhea, coughing, Most patients initially are presented for veterinary care because of
or weight loss. Because spontaneous HAC typically affects elderly the typical clinical signs of HAC, particularly once they affect the
dogs, the signs initially may be attributed to normal aging. The quality of life of the patient or the owner. Pituitary tumors may
progress of the disorder is generally insidious, but eventually the be detected by CT, dynamic CT, 26,27 MRI, 4,6,28–32 or dynamic
4,6
owners of affected dogs seek veterinary care because of frustra- MRI ; however, these techniques are not routinely performed
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tion with signs such as polyuria, polydipsia, panting, and exercise in all dogs diagnosed with PDH. In most cases the diagnosis is
intolerance. based on the presence of typical clinical signs and clinicopatho-
The clinical signs in dogs with HAC are the result of the glu- logic changes of hypercortisolemia, together with the results of
coneogenic, catabolic, immunosuppressive, and anti inflamma- endocrine testing.
tory effects of excessive circulating glucocorticoids. These signs As noted previously, brain imaging is not performed in most
include polyuria, polydipsia, polyphagia, abdominal enlargement, dogs with PDH, and most receive treatment to address adre-
lethargy, panting, exercise intolerance, muscle weakness, alopecia, nal hyperfunction rather than the pituitary tumor itself. This is
calcinosis cutis, thinning of the skin, poor wound healing, muscle most likely because brain imaging and pituitary surgery or radia-
wasting, decreased bone density, and reproductive abnormalities. tion therapy (RT) is not affordable or accessible to many clients.
Dogs with HAC are also predisposed to diabetes mellitus and Although medical therapy for PDH has a long history of success-
are more susceptible to infection, particularly urinary tract infec- ful use, it is important to note that the pituitary lesion in dogs
tions. More serious disorders associated with canine HAC include with PDH will progress over time. In a study of 13 dogs that
hypertension and proteinuria. Although uncommon, pulmonary underwent MRI evaluation of the brain at the time of diagnosis of
thromboembolism is another potentially life-threatening compli- PDH and before medical therapy was instituted, eight of the dogs
cation of HAC. had a visible pituitary mass and none of the dogs had clinical signs
The most commonly used screening tests for HAC are the low- of neurologic disease. Four of the dogs showed enlargement of
31
dose dexamethasone suppression test (LDDST) and the ACTH the pituitary tumor on MRI 1 year later, and a pituitary tumor
stimulation test. For patients with typical clinical signs of HAC also was detected in two dogs that did not have a visible mass on
and positive results on a screening test, further testing is often the initial MRI. Two of the 13 dogs had developed neurologic
necessary to differentiate between pituitary- and adrenal-depen- signs at the time of the 1-year follow-up MRI. In a study evaluat-
dent disease. Differentiation tests that are commonly used include ing diagnostic imaging findings in 157 dogs with PDH with and
the high-dose dexamethasone suppression test (HDDST) and the without neurologic signs, central nervous system (CNS)–specific
measurement of endogenous ACTH levels. The interested reader signs such as circling, seizures, and ataxia were neither sensitive nor
should consult the many excellent resources that provide further specific for predicting the presence of a pituitary macrotumor.
6
detail on the clinical and clinicopathologic findings in dogs with However, signs such as lethargy, mental dullness, and decreased
HAC, in addition to extensive discussion of the pros and cons of appetite were highly specific for detection of a pituitary macrotu-
the different screening and differentiation tests. 9,10,12 mor but not highly sensitive. Other studies also have documented
The results of imaging studies, including ultrasonography, that mentation and appetite changes are the most common signs
computed tomography (CT), or magnetic resonance imaging associated with pituitary tumors. 5,34
(MRI), may assist in distinguishing between PDH and ADH. When considering brain imaging in dogs with PDH, several
Abdominal ultrasonography should not be used as a screening test factors should be taken into account: 40% to 50% of dogs with
for HAC, and it should also not be used as the sole mechanism for PDH have tumors that are not visible on CT or MRI, and these
discriminating between PDH and ADH; however, it can provide dogs are unlikely to develop neurologic signs associated with the
useful information. 13–17 The adrenals of patients with PDH are tumor; 15% to 25% of dogs with PDH are at risk for the devel-
often bilaterally enlarged with increased thickness; they typically opment of neurologic signs as the result o the presence of an
14
maintain a normal shape and are homogeneous in echogenicity. enlarging tumor, and these signs typically develop within 6 to 18
However, there can be overlap between adrenal gland measure- months of the diagnosis of PDH; brain imaging may be helpful
ments in normal dogs, dogs with nonadrenal disease, and dogs in predicting dogs likely to develop neurologic signs in patients
with HAC. Adrenal gland asymmetry may also be detected in with PDH that initially have no signs directly attributable to
35
dogs with PDH because of nodular hyperplasia. In some cases the tumor ; and if RT is being considered, early treatment will
this appearance can be confused with adrenal neoplasia. To further likely improve the prognosis. 5,36 One approach that has been
complicate the diagnostic accuracy of abdominal ultrasonogra- suggested is that CT or MRI should be considered at the time of
phy, a small percentage of patients with HAC may have concur- diagnosis of PDH, with medical therapy alone recommended if
18
rent PDH and ADH. Bilateral adrenal tumors may also occur, no mass is seen. If a pituitary mass is detected but is less than 8