Page 919 - Small Animal Internal Medicine, 6th Edition

CHAPTER 50 Disorders of the Adrenal Gland 891

TABLE 50.6
VetBooks.ir Adrenal Tumors Reported in Dogs and Cats TESTS TO ESTABLISH

HORMONE SECRETED SPECIES CLINICAL SYNDROME DIAGNOSIS

Nonfunctional None Dog,* Cat — Diagnosis by exclusion
adrenal tumor histopathology
Functional Cortisol Dog,* Cat Hyperadrenocorticism Urine C:C ratio
adrenocortical Cushing’s syndrome Low-dose dexamethasone
tumor suppression test
+
Aldosterone Cat,* Dog Hyperaldosteronism Serum K and Na +
Conn’s syndrome Baseline plasma aldosterone
Progesterone Cat,* Dog Mimics Serum progesterone
hyperadrenocorticism
Steroid hormone precursors
17-OH-progesterone Dog, Cat Mimics ACTH stimulation test—
hyperadrenocorticism measures steroid hormone
precursors
Desoxycorticosterone Dog Mimics ACTH stimulation test—measures
hyperaldosteronism steroid hormone precursors
Functional Norepinephrine Dog,* Cat Pheochromocytoma Urine normetanephrine to
adrenomedullary Epinephrine creatinine ratio; Plasma free
tumor normetanephrine concentration
ACTH, Adrenocorticotropic hormone.
*Species most commonly affected.

relies on histologic evaluation of the surgically excised protocol for the management of hypertension in dogs with
adrenal mass. pheochromocytoma includes preoperative phenoxybenza-
mine and intraoperative phentolamine. The initial dosage
Treatment of phenoxybenzamine is 0.5 mg/kg q12h. Unfortunately,
A period of medical therapy intended to reverse the effects many dogs with pheochromocytoma have episodic clinical
of excessive adrenergic stimulation, followed by surgical signs and hypertension, making it difficult to adjust dosage
removal of the tumor, is the treatment of choice for pheo- on the basis of improvement in clinical signs and blood
chromocytoma. The success of chemotherapy and radiation pressure. In addition, this dosage is often ineffective in pre-
therapy in humans with pheochromocytoma has been venting severe hypertension during surgery. Therefore we
limited, and results of chemotherapy or radiation therapy for gradually increase the phenoxybenzamine dosage every 3
the treatment of pheochromocytoma in dogs or cats have not to 4 days until clinical signs of hypotension (e.g., lethargy,
been reported. Mitotane and trilostane are ineffective for weakness, syncope), adverse drug reactions (e.g., vomiting),
tumors arising from the adrenal medulla and are not recom- or a maximum dosage of 2 mg/kg q12h is attained. Surgery
mended. Long-term medical therapy is primarily designed is recommended 1 to 2 weeks later either by laparotomy or
to control excessive catecholamine secretion. laparoscopic adrenalectomy. The drug should be continued
Potentially life-threatening complications are common until the time of surgery. Complications may occur despite
during the perioperative period, especially during induc- prior treatment with α-adrenergic blocking drugs; close
tion of anesthesia and manipulation of the tumor during monitoring of the dog during the perioperative period is
surgery. The most worrisome complications include episodes critical for a successful outcome after adrenalectomy. (See
of acute, severe hypertension (systolic arterial blood pressure Suggested Readings for more information on the periopera-
> 300 mm Hg), episodes of severe tachycardia (heart rate tive and surgical management of dogs with a pheochromo-
> 250 beats/min) and arrhythmias, and hemorrhage. Pre- cytoma.) In a study by Herrera et al. (2008), the significant
operative α-adrenergic blockade using phenoxybenzamine prognostic indicators for survival after adrenalectomy for
helps control potentially life-threatening fluctuations of blood pheochromocytoma included lack of intraoperative arrhyth-
pressure and heart rate during anesthesia and surgery. The mias, decreased surgical time, younger age, and pretreat-
dose and frequency of phenoxybenzamine administration ment with phenoxybenzamine.
and the duration of therapy required to adequately achieve Medical management with α-adrenergic blockade is rec-
desired effects have not been defined for dogs. Our current ommended whenever pheochromocytoma is suspected and