Page 590 - Withrow and MacEwen's Small Animal Clinical Oncology, 6th Edition

568 PART IV Specific Malignancies in the Small Animal Patient

In a prospective study of 150 dogs treated with transsphenoidal treatment of pituitary tumors are beneficial. Five of 14 dogs with
hypophysectomy for PDH, the 1-, 2-, 3-, and 4-year estimated PDH in this study were reported to show resolution of clinical
signs of HAC, together with at least one normal ACTH stimula-
survival rates were 84%, 76%, 72%, and 68%, respectively.
VetBooks.ir Twelve dogs died postoperatively, and 127 went into remission, tion test result after completion of RT. A recent nonrandomized
5
observational study compared two coarse fractionated radia-
of which 32 later experienced a recurrence of disease. Complica-
tions included central diabetes insipidus in 53% of dogs under- tion protocols for canine pituitary macrotumors and found that
going remission and incomplete hypophysectomy in nine dogs. dogs treated with 10 fractions of 3.8 Gy/fraction on a Monday/
The overall success rate of transsphenoidal hypophysectomy was Wednesday/Friday protocol had a longer ST than dogs treated
determined to be 65% in this study. Reported complications once weekly to a total dose of 38 Gy. 64
54
of transsphenoidal hypophysectomy include hemorrhage, electro- Most of the reports that document the use of RT for the treat-
lyte imbalance, postoperative neurologic deficits, decreased tear ment of pituitary tumors in dogs provide little detailed informa-
production, thromboembolic disease, recurrence of PDH, and tion about the progress of the clinical syndrome of HAC in these
perioperative death. 54,56 However, the overall outcome of this patients. Therefore, although RT appears effective in controlling
procedure is favorable, resulting in rapid resolution of disease and neurologic signs and increasing survival, it is difficult to predict
5
a long period of remission or complete resolution in patients that the endocrinologic outcome of RT for dogs with PDH. Current
survive the perioperative period. 53,56 and future developments in the use of RT for the management of
Although most of the publications on the surgical manage- canine PDH likely will include the more widespread use of stereo-
ment of canine pituitary tumors originated in Europe, this tech- tactic RT (SRT; see Chapter 13).
nique is becoming more widely available in the United States. A
recent publication documented the outcome of transsphenoidal Feline Pituitary-Dependent
surgery using a high-definition video telescope, and this approach Hyperadrenocorticism
is now available at Washington State University Veterinary Teach-
ing Hospital. In this case series of 26 dogs with PDH, the overall As noted previously, approximately 80% to 85% of cases of HAC
mortality associated with the surgery was 19%; however, the five in the cat are the result of pituitary disease. 66–68 Most of these
deaths occurred in the first 10 dogs treated, with no mortality in cats will have a pituitary adenoma that secretes excessive ACTH;
69
55
the subsequent 16 dogs. This serves as a reminder that transs- however, pituitary carcinoma has been reported, and cases have
phenoidal hypophysectomy is a specialized procedure with a steep been described of cats with pituitary tumors that secrete other
learning curve. A successful outcome is most likely with careful hormones in addition to ACTH. 70–72 Cushing’s syndrome is
patient selection and a coordinated approach from a team of spe- considerably less common in cats than in dogs, and in general
2
cialists in surgery, medicine, neurology, and critical care. affected cats are much more “sick” than their canine counterparts.
The mean age of cats with PDH is approximately 10 years. Feline
Radiation Therapy HAC is commonly associated with insulin-resistant diabetes mel-
Several reports have been published on the successful use of litus, with signs of polyuria, polydipsia, polyphagia, and weight
radiation in the treatment of canine PDH. 5,36,61–65 Dow and col- loss. Cats with HAC often have a potbellied appearance as a result
leagues treated six dogs with functional pituitary macrotumors; of hepatomegaly and muscle weakness, and they frequently have
the dogs were given 40 Gy in 10 equal fractions. The MST was thin, fragile skin that tears and bruises easily. The clinician should
743 days; neurologic signs resolved in all the dogs; and ACTH lev- keep this in mind when examining these cats and performing
els remained high for at least 1 year after therapy. Cobalt 60 RT diagnostic tests, because it is easy to cause significant, debilitat-
61
was used to treat six dogs with PDH caused by a pituitary tumor ing skin damage. Additional clinical signs include lethargy, gen-
that was detectable on MRI; tumor size was significantly reduced eralized muscle atrophy, weakness, alopecia, and an unkempt hair
in all cases, but clinical signs of PDH were adequately controlled coat (Fig. 26.1).
62
only in one dog. The effects of megavoltage irradiation on pitu- On routine laboratory testing, increased alkaline phosphatase
itary tumors was evaluated in 24 dogs with neurologic signs; 10 activity is much less frequently detected in cats with HAC com-
dogs experienced complete remission of neurologic signs, and pared to dogs. Cats may have increased alanine aminotransferase
another 10 dogs achieved partial remission; 4 dogs died, either activity, hypercholesterolemia, azotemia, and a minimally concen-
36
during radiation therapy or shortly thereafter. As in previous trated urine. Hyperglycemia and glycosuria are expected in cats
studies a correlation was noted between relative tumor size and with concurrent diabetes mellitus. No consistent complete blood
the severity of neurologic signs in dogs with pituitary tumors. A count (CBC) changes have been reported in cats with HAC. Tests
correlation between tumor size and remission of neurologic signs used to screen for spontaneous HAC in cats include the urine
also was noted after pituitary irradiation, which suggests that early cortisol:creatinine ratio, ACTH stimulation test, and LDDST.
treatment of these tumors should improve the prognosis, although It is important to note that the details of these protocols differ
36
control of ACTH secretion was unlikely. A retrospective study between dogs and cats; readers are directed to more complete ref-
of RT for the treatment of pituitary masses demonstrated signifi- erences for further information. 66–68 The HDDST, endogenous
cantly improved STs and control of neurologic signs in 19 dogs ACTH concentrations, and abdominal ultrasound examination
that received RT compared to 27 untreated control dogs with may be used to assist in differentiation of PDH from ADH in
pituitary masses. The mean ST in the treated group was 1405 the cat. 73
5
days, compared to 551 days in the nonirradiated group. The 1-, Because PDH is relatively uncommon in the cat, there have
2-, and 3-year estimated survival rates were 93%, 87%, and 55% historically been few case series and case reports on which to
for the irradiated dogs and 45%, 32%, and 25% for the nonirradi- base treatment recommendations. However, recent years have
ated dogs, respectively. yielded some additional information about the management of
Treated dogs with smaller tumors lived longer than those this condition. Direct treatment of the pituitary tumor has been
with larger tumors; again, this suggests that early diagnosis and reported with either surgical hypophysectomy or RT. 52,66,70,74–76