Page 265 - Problem-Based Feline Medicine

15 – THE CAT WITH POLYURIA AND POLYDIPSIA 257

Clinical signs are mainly of hypokalemia including
PHEOCHROMOCYTOMA
muscle weakness, ventroflexion of the neck, inappe-
tence and weight loss, or of hypertension and include
Classical signs
blindness from hypertensive retinopathy. Other signs
include ataxia, abdominal enlargement and polyuria ● Polyuria, polydipsia.
and/or polydipsia with two of the five reported feline ● Signs of systemic hypertension (blindness,
cases also having diabetes mellitus. dyspnea from heart failure).

Diagnosis
Pathogenesis
Serum creatinine kinase activity is increased reflecting
Pheochromocytoma is a rare tumor, that develops
hypokalemic myopathy.
from the medullary region of the adrenal gland, or
Urine specific gravity is usually dilute. occasionally as an extra-adrenal mass.
A presumptive diagnosis is based on finding persistent Functional tumors may produce adrenaline (epineph-
hypokalemia despite supplementing with high doses rine), noradrenaline (norepinephrine) and occasion-
of potassium, and intractable hypertension in an eld- ally other hormones such as dopamine.
erly cat. The finding of an adrenal mass and increased
Signs result from either elevated catecholamine con-
aldosterone concentrations help confirm the diagnosis.
centrations or from a mass effect of the tumor, metas-
tasis or local invasion.
Differential diagnosis
Excessive catecholamine concentrations may produce
Pheochromocytoma may also cause hypertension in severe hypertension and associated signs such as reti-
an elderly cat and be associated with an adrenal mass. nal hemorrhage and detachment.
Other causes of hypertension in elderly cats including Polyuria and polydipsia may result directly from the
hyperthyroidism and renal disease need to be ruled excessive catecholamine concentrations, hypertensive
out. renal damage or from insulin resistance. In diabetic cats
with unexplained insulin resistance, pheochromocy-
toma is a rare potential cause.
Treatment
Clinical signs can be improved or resolved with potas-
Clinical signs
sium supplementation and antihypertensive
therapy. Affected cats are typically old, ranging from 10–20
● Use potassium gluconate solution, tablets or pow- years.
der (4–10 mmol (mEq)/cat PO q 24 h in divided
doses. See treatment of hypokalemia in The Cat Clinical signs are vague and diagnosis pre-mortem is
With Generalized Weakness (page 946) and The rare. Signs include polyuria and/or polydipsia. In dia-
Cat With Neck Ventroflexion (page 895). betic cats, pheochromocytoma may result in poor
● Use amlodipine (0.625 mg or 1/4 of a 2.5 mg glycemic control associated with insulin resistance.
tablet, PO q 24 h) for hypertension. Some cats with Sudden blindness with evidence of retinal hemorrhage
severe hypertension may require doses as high as and detachment has been reported as well as congestive
1.25 mg PO q 12 h. Titrate dosage carefully, based heart failure.
upon blood pressure determinations.
● Trilostane has been used in humans with hyperal-
dosteronism, but its use has not been reported in Differential diagnosis
cats.
Primary hyperaldosteronism may also cause hyper-
Long-term resolution involves surgical removal of the tension in an elderly cat and be associated with an adre-
adrenal mass. nal mass. Typically there is hypokalemia, which is