Page 918 - Small Animal Internal Medicine, 6th Edition

890 PART VI Endocrine Disorders

TABLE 50.5 catecholamine excess, dogs with an unexpected adrenal mass
identified by abdominal ultrasound, and dogs that develop
VetBooks.ir Clinical Signs and Physical Examination Findings unexpected problems with systemic hypertension, nasal or
retinal hemorrhage, or cardiac arrhythmia during anesthe-
Associated With Pheochromocytoma in Dogs
PHYSICAL EXAMINATION sia. Pheochromocytoma may also be an unexpected or inci-
dental finding at necropsy or may cause sudden collapse and
CLINICAL SIGNS FINDINGS death from a sudden, massive, and sustained release of cat-
echolamines by the tumor.
Intermittent weakness* No identifiable
Intermittent collapsing abnormalities* No consistent abnormalities are identified in the CBC,
episodes* Panting, tachypnea* serum biochemistry panel, or urinalysis that would raise
Intermittent panting* Weakness* suspicion for pheochromocytoma. Many abnormalities
Intermittent tachypnea* Tachycardia* identified in results of routine blood and urine tests are
Intermittent anxious Cardiac arrhythmias caused by concurrent disorders that are commonly present
behavior* Weak pulses in dogs with pheochromocytoma or are nonspecific find-
Polyuria, polydipsia Pale mucous membranes ings affiliated with hypertension. A history of acute or epi-
Lethargy Muscle wasting* sodic collapse, identification of appropriate respiratory and
Inappetence Findings from systemic cardiac abnormalities during physical examination, docu-
Vomiting hypertension: mentation of systemic hypertension, and identification of
Diarrhea Nasal hemorrhage
Weight loss Oral hemorrhage an adrenal mass by abdominal ultrasonography are most
Abdominal distention Retinal hemorrhage helpful in establishing a tentative diagnosis of pheochro-
Rear limb edema Retinal detachment mocytoma. Systemic hypertension may be sustained or epi-
Lethargy sodic. Failure to document systemic hypertension in a dog
Abdominal pain with appropriate clinical signs does not rule out a diagnosis
Palpable abdominal mass of pheochromocytoma.
Ascites Ultrasound identification of an adrenal mass with a
Rear limb edema normal-size contralateral adrenal gland is perhaps the most
important clue for pheochromocytoma. Pheochromocytoma
*Common signs and physical examination findings. is one of several differentials for an adrenal mass (Table 50.6;
see also the discussion of incidental adrenal mass). Pheo-
Clinical signs and physical examination findings develop chromocytomas cannot be distinguished from other tumors
as a result of the space-occupying nature of the tumor and in the adrenal gland on the basis of sonographic appearance,
its metastatic lesions, as a result of excessive secretion of although identification of hypoechoic foci within the tumor
catecholamines, or as a result of spontaneous hemorrhage is suggestive of pheochromocytoma. Regardless, the primary
from the tumor into the retroperitoneal cavity (Table 50.5). differential diagnosis for an adrenal mass is ADH. Many of
The most common clinical signs and physical examination the clinical signs (e.g., panting, weakness) and blood pres-
abnormalities involve the respiratory, cardiovascular, and sure alterations seen in dogs with hyperadrenocorticism
musculoskeletal systems and include generalized weakness, (common) are similar to those observed in dogs with pheo-
anorexia, weight loss, episodic collapse, agitation, nervous chromocytoma (uncommon). In addition, both pheochro-
behavior, excessive panting, tachypnea, and tachycardia. mocytoma and adrenocortical carcinoma invade adjacent
Excess catecholamine secretion may also cause severe sys- structures and cause tumor thrombi in the phrenicoabdomi-
temic hypertension, resulting in nasal and retinal hemor- nal vein and caudal vena cava. It is important to rule out
rhage, retinal detachment, acute blindness and epistaxis. ADH before focusing on pheochromocytoma in a dog with
Catecholamine secretion by a pheochromocytoma typically an adrenal mass.
is episodic and random, not sustained. Therefore clinical Measurement of urinary catecholamine concentrations
signs tend to be paroxysmal and usually are not evident at is being used with increased frequency to aid in the diag-
the time the dog is examined; the physical examination often nosis of pheochromocytomas. Urine normetanephrine-
does not provide clues to the presence of a pheochromocy- to-creatinine ratios and plasma-free normetanephrine can
toma because a catecholamine surge usually is not happening strengthen the tentative diagnosis of pheochromocytoma,
at the time the dog is examined. Because clinical signs and but do not provide a definitive diagnosis. Urine normeta-
physical examination findings are often vague, nonspecific, nephrine ratio or plasma free-normetanephrine concentra-
and easily associated with other disorders, pheochromocy- tions greater than or equal to four times the upper limit
toma often is not considered a possible differential diagnosis of the reference range increase the probability of a pheo-
until an adrenal mass is identified on abdominal ultrasound. chromocytoma to nearly 100%; with smaller increases a
pheochromocytoma may or may not be present. Proper
Diagnosis sample handling and species specific reference ranges are
Pheochromocytoma should be on the list of differential diag- critical for accurate results and interpretation. The antemor-
noses for dogs presenting with clinical signs suggestive of tem definitive diagnosis of a pheochromocytoma ultimately