Page 122 - Clinical Small Animal Internal Medicine

90 Section 2 Endocrine Disease

hypokalemia and/or hypertension, determining whether
VetBooks.ir hyperaldosteronism is primary (PHA) or secondary
(hyperreninemic hyperaldosteronism) can be a diagnos-
tic challenge.

Epidemiology
Primary hyperaldosteronism is rare. However, because
several of the diagnostic findings associated with PHA
are also associated with chronic kidney disease, PHA is
likely underdiagnosed.

Figure 11.1 A 13‐year‐old male neutered domestic shorthair
Signalment presented for acute blindness due to severe hypertension
Middle‐aged to older cats are predisposed (median age (>250 mmHg, as measured by Doppler). Note the mydriasis with
complete bullous retinal detachment and retinal hemorrhages.
13 years; range 5–20 years), but there does not appear to Source: Photo courtesy of Martin Coster, DVM, MS, DACVO.
be a sex or breed predisposition.

mydriasis (Figure 11.1). Subclinical retinal lesions are
History and Clinical Signs
often identified in cats with myopathy, as well.
The most common clinical signs are associated with
hypokalemia and systemic arterial hypertension; polyu- Diagnosis
ria, polydipsia, weight loss, and a palpable abdominal
mass may also be noted (Box 11.1). Hypokalemic myopa- The diagnostic evaluation of a cat for PHA includes blood
thy can be acute or chronic in onset and clinical signs can pressure measurement, complete blood count, serum
be mild or severe. Affected cats often have cervical ven- biochemistry, urinalysis, imaging, and specific hormone
troflexion, a plantigrade stance, difficulty jumping, and/ testing. Cats with idiopathic adrenal hyperplasia are more
or severe weakness. Forelimb stiffness followed by acute likely to be hypertensive, with a median systolic blood
collapse and dysphagia have also been reported. Whereas pressure of 210 mmHg (range, 185–270 mmHg) in one
most cats with PHA caused by adrenocortical tumors study. Median systolic BP in cats with neoplasia was
present for hypokalemic myopathy, fewer of the cats 185 mmHg (range, 160–250 mmHg) in another study.
with idiopathic adrenal hyperplasia display this clinical Hypertension is often difficult to control in cats with
feature. PHA, and PHA should be suspected in cats with refrac-
Ocular changes due to hypertension are more com- tory hypertension.
mon with idiopathic adrenal hyperplasia, and may The CBC does not usually reveal any significant abnor-
include retinal detachment and sub‐ and intraretinal and malities in patients with PHA. Moderate to severe
intravitreal hemorrhages. Cats with these lesions usually hypokalemia is often evident on the serum biochemistry
present for acute‐onset blindness, hyphema, and/or profile, although not all cats with PHA are hypokalemic.
Significant signs of hypokalemic myopathy are not usu-
ally obvious until potassium concentrations decrease to
less than 2.5 mmol/L, but this is variable. Creatine kinase
Box 11.1 Clinical findings in cats is markedly increased in cases of hypokalemic myopathy.
with hyperaldosteronism Hypernatremia is uncommon, likely because of dilution
from volume expansion.
Due to hypokalemia: Some cats with PHA are also mildly to moderately
Cervical ventroflexion azotemic, and often develop progressive renal disease as
Plantigrade stance a consequence of PHA. This is more common in cats with
Difficulty jumping idiopathic adrenal hyperplasia. Determining whether
Weakness
Due to hypertension (systolic BP >180 mmHg): hyperaldosteronism is a consequence of chronic kidney
disease, or vice versa, can be difficult and relies on meas-
Ocular changes urement of plasma renin activity, which is not readily
Acute blindness available in the US. Interestingly, phosphorus concentra-
Hyphema tion is often at the lower end of the reference range and
Mydriasis
Polyuria/polydipsia does not become increased with progressive azotemia in
cats with PHA. The reason for this is unclear but may be