Case REPORT
Horse or zebra? A case of feline hyperaldosteronism Grace Kaemper BVSc
(dist.)
Introduction
Hyperaldosteronism is the most common adrenal endocrine disease in cats (Kooista 2020). The true frequency is difficult to determine, as it is generally regarded to be underdiagnosed (Schulman 2010). This case study examines the presenting signs, diagnosis, and treatment of feline hyperaldosteronism; and proposes that this not uncommon endocrine disease should be routinely put on differential diagnosis lists when presented with hypertensive or hypokalaemic cats, rather than considered a ‘zebra’.
Case history
A 12-year-old female spayed domestic short hair cat presented for acute onset of blindness. The cat had mildly increased water intake, but there were no other significant historical findings.
Clinical findings
On physical exam, there was bilateral mydriasis, and menace and pupillary light reflexes were absent. There was no pain on ocular retropulsion. Ophthalmoscopic examination revealed regions of retinal haemorrhage. Systemic arterial blood pressure was measured as 280 mmHg using a Doppler flow detector, therefore hypertensive retinopathy was diagnosed. The physical exam was otherwise within normal limits. An in-house biochemistry renal panel (Kidney Profile Plus; Abaxis, Griesheim, Germany) revealed moderate hypokalaemia of 2.8 (reference range 3.7–5.8) mmol/L, and mild elevations in the concentration of urea and content of tCO2. The concentration of creatinine was within normal limits, as were other electrolytes.
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Hypertensive retinopathy and hypokalaemia were the key clinical findings. Hypertension can be idiopathic but is more commonly secondary to another pathology (Acierno et al. 2018). In cats, the most common causes are hyperthyroidism, chronic kidney disease, hyperaldosteronism, protein losing nephropathy, and less commonly diabetes mellitus (Acierno et al. 2018). The combination of hypertension and hypokalaemia made hyperaldosteronism the most likely differential.
Further diagnostic findings
Hyperthyroidism was ruled out by a normal concentration of free thyroxine (T4) (T4/Cholesterol Test; Abaxis) in serum. In-house urinalysis collected by cystocentesis showed a urine specific gravity of 1.043, negative glucose, 2+ protein and an inactive sediment; thereby ruling out chronic kidney disease, protein-losing nephropathy and diabetes mellitus. Although there was moderate proteinuria, this was most likely secondary to hypertension rather than the cause. An aldosterone assay was run on frozen serum resulting in a concentration of 1,430 pmol/L. A study by Yu et al. (1998) found the median plasma aldosterone concentration of healthy cats was 161 pmol/L. As the upper value set by the laboratory for healthy domestic cats was 700 pmol/L, this result confirmed the diagnosis of primary hyperaldosteronism.
Treatment
While waiting for the results of the aldosterone assay, symptomatic treatment with 0.65 mg/cat amlodipine (Amodip 1.25 mg; CEVA Animal Health Pty Ltd, Glenorie, Australia) once daily and oral potassium gluconate supplementation at 0.5 mEq/kg (Kaminox 2 mEq/2mL; VetPlus Ltd, Docklands, UK) were initiated. The amlodipine dose was increased to 1.25 mg/cat once daily after 1 week due to
insufficient response. Two weeks after starting treatment, the diagnosis of hyperaldosteronism was confirmed, and spironolactone (Spiractin 25mg; Mylan New Zealand Ltd, Auckland, NZ) was initiated at a dose of 2 mg/kg twice daily. At this point, systolic blood pressure had decreased to a mean of 148 mmHg, which fell within the ideal range. However shortly after beginning treatment with spironolactone, the cat developed acute forelimb pain and lethargy due to hypokalaemic myopathy. Persistent hypokalaemia of 3.2 mmol/L was confirmed despite oral supplementation. Intravenous potassium supplementation was provided with 10 mEq/L potassium chloride (Biomed Ltd, Auckland, NZ) and Metabolase (Ethical Agents Ltd, Auckland, NZ) added into a constant rate infusion of 0.9% NaCl at 9 mL/hour. Treatment was unsuccessful and the cat entered cardiac arrest.
Discussion
Hyperaldosteronism is the most common adrenal endocrine disease in cats (Kooistra 2020). However, the true frequency is difficult to determine, as it is generally regarded to be underdiagnosed (Schulman 2010). Lo et al. (2014) estimate that primary adrenal tumours make up 0.2% of all neoplasms in cats. Many studies argue that hyperaldosteronism should be considered as a differential when middle-aged to older cats present with either hypertension or hypokalaemia (Ash 2005, Kooistra 2020). One proposed reason for underdiagnosis is that chronic kidney disease is blamed for hypertension and hypokalaemia, and no further diagnostics are performed (Javardi et al. 2005). In reality, hyperaldosteronism can accelerate the progression of CKD and the two diseases are present concurrently in a proportion of azotaemic cats (Javardi et al. 2005). Aldosterone is secreted from the zona glomerulosa in the adrenal cortex. In a healthy animal, its release is regulated by
Companion Quarterly: Official Newsletter of the Companion Animal Veterinarians Branch of the NZVA | Volume 33 No 1 | March 2022
