A 13-year-old 10.3-lb (4.68-kg) spayed female domestic shorthaired cat was presented to the VCA West Los Angeles Animal Hospital
for progressive and unresolving lethargy over the course of two to three days and one episode of vomiting. The owner reported
that the cat recently showed an inability or unwillingness to jump onto elevated surfaces and described signs consistent with
a plantigrade hindlimb stance that was episodic in nature. The cat was otherwise healthy with no preexisting conditions and
was receiving no medications. It lived in a household as the sole pet and was indoor-only, and there was no known exposure
to or ingestion of toxins.
On physical examination, the cat was quiet, alert, and responsive, with a body condition score of 5/9. The cat's vital signs
were normal (temperature = 101.4 F [38.6 C]; heart rate = 140 beats/min; respiratory rate = 30 breaths/min), and the cat appeared
to be mildly dehydrated with tacky mucous membranes. A grade II/VI left systolic parasternal heart murmur was detected on
thoracic auscultation. Musculoskeletal examination revealed cervical ventroflexion and generalized weakness.
In-house and laboratory diagnostics were performed, and selected results are shown in Table A. A thoracic radiographic examination revealed mild cardiomegaly with normal pulmonary parenchyma and vasculature. After the
initial in-house blood analysis and thoracic radiographic examination, the differential diagnoses included hyperthyroidism,
hypokalemic nephropathy, pyelonephritis, primary hyperaldosteronism, and cardiomyopathy.
The cat was hospitalized and initially started on lactated Ringer's solution with 40 mEq/L of potassium chloride at a maintenance
rate of 50 ml/kg/day. The next morning, samples were collected for outside evaluation, and the results are presented in Table B. Potassium concentrations were monitored every six hours, and the potassium chloride supplementation in intravenous fluid
was adjusted accordingly. Oral potassium gluconate supplementation (2 mEq every eight hours) and amoxicillin trihydrate-clavulanate
potassium (13.75 mg/kg every 12 hours) were instituted.
The cat's blood pressure was measured by using a Doppler monitor every six hours for 24 hours. A mean systolic value, calculated
from at least three consecutive measurements, was reported. Over 24 hours, the cat's blood pressure ranged from a mean systolic
of 180 to 195 mm Hg. Retinal examination revealed bilateral tortuous vessels and mild focal hemorrhage of the right eye. The
cat was started on amlodipine (0.625 mg orally every 24 hours).
After analysis of the commercial laboratory data (Table B), hyperthyroidism appeared to be unlikely, so abdominal ultrasonography was recommended in addition to measurement of plasma