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.
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 aldosterone concentration.
Definitive diagnosis and treatment
An abdominal ultrasonographic examination revealed an enlarged right adrenal gland measuring 1.23 x 1.48 cm. The left adrenal gland was visualized and measured 3.2 mm (normal width) in a dorsoventral plane. The kidney size and architecture appeared normal, with no evidence of renal pelvic or ureteral dilatation. The liver, spleen, gastrointestinal tract, and urinary bladder appeared normal ultrasonographically. No enlarged mesenteric lymph nodes were seen, and the remainder of the study findings were unremarkable.
Spironolactone (1.5 mg/kg orally every 12 hours) was added to the treatment plan. The dose of potassium gluconate was increased to 4 mEq given orally every eight hours because the potassium concentration was rechecked and remained below the reference range. Serial recheck electrolyte profiles revealed progressively increasing potassium concentrations. The cat's generalized weakness improved along with resolution of the cervical ventroflexion. The resting plasma aldosterone concentration (PAC) was > 3,864 pmol/L (reference range = 194 to 388 pmol/L). This value, along with the ultrasonographic findings and interpretation of minimum database diagnostics excluding other differentials for hypokalemia and hypertension, confirmed a diagnosis of hyperaldosteronism.
Surgical excision of the adrenal mass was recommended to the owners, but it was declined because of financial considerations. Medical management was implemented. The cat was discharged with amlodipine (0.625 mg orally every 24 hours), spironolactone (6.25 mg orally every 12 hours), amoxicillin trihydrate-clavulanate potassium (62.5 mg total orally every 12 hours for seven days) and potassium gluconate (6 mEq orally every 12 hours).
An initial recheck evaluation 10 days after discharge revealed a potassium concentration of 4.13 mEq/L and a systolic blood pressure of 130 mm Hg. The cat's owner reported improvement in the cat's weakness and lethargy, as well as return of usual jumping behaviors and normal gait and stance. A urine culture sample collected by cystocentesis was repeated after the antibiotics were discontinued, and the results were negative for growth.
Subsequent evaluations were performed every two months, and the cat remained normotensive with normal potassium concentrations. At the time of this manuscript, 19 months after diagnosis, the cat is reported to be doing well.