Systemic hypertension has been recognised with increasing frequency in small animal practice over the past 20 years. Although there is still some debate regarding optimal cut-off values, risk categories suggested within the ACVIM consensus statement have been widely adopted (Table 1).¹

Table 1. Risk categories associated with systemic hypertension in dogs and cats¹

Consequences of uncontrolled hypertension can be severe. End-organ damage most commonly involves the eye, brain, kidney, or heart and consequences include blindness, cerebrovascular events, hypertensive encephalopathy, myocardial hypertrophy, and progressive kidney disease. Whilst hypertension can be controlled medically, assessment for the underlying cause is critical. There are numerous potential causes of hypertension including kidney disease, obesity, pain, stress, and certain drugs.

Essential hypertension is less clearly defined in dogs or cats. Other causes primarily relate to the endocrine system and include hypo- and hyperthyroidism, hyperadrenocorticism, phaeochromocytoma, primary hyperaldosteronism, and diabetes mellitus. Hypertension has been reported in from 5 to 22% of hyperthyroid cats. In most cases the hypertension is mild and probably stress related. If severe and associated with clinical consequences, other causes of hypertension, such as renal disease, should be investigated. Although suggested to occur in hypothyroidism, evidence is limited. Hyperadrenocorticism is commonly associated with mild to severe hypertension in dogs. However, despite this, clinical signs associated with hypertension are rarely reported.¹ As such dogs are not usually presented primarily with hypertension, but rather the clinical signs of hyperadrenocorticism predominate.

Severe hypertension is more often a feature of phaeochromocytoma in dogs. Given that this may often be the sole presenting complaint, other than vague and non-specific signs, investigation for phaeochromocytoma is indicated in all older animals presenting with hypertension. Demonstration of an adrenal mass together with increased urinary normetanephrine to creatinine ratio or plasma free metanephrine concentration appear the most promising for its diagnosis.²

Primary hyperaldosteronism (Conn’s syndrome) is caused by the excessive autonomous secretion of mineralocorticoids. It is rare in dogs and may be an underdiagnosed condition in cats. Most cases are due to the presence of an adrenocortical carcinoma or adenoma although adrenal hyperplasia has also been described. Clinical signs relate to systemic hypertension, hypokalaemia, or both. Muscle weakness, including cervical ventroflexion, and sudden onset blindness are most commonly reported. Adrenal ultrasonography will reveal an adrenal mass in most cases and circulating aldosterone concentrations, either alone or after ACTH stimulation, are high. Although demonstration of decreased renin activity is required for definitive diagnosis, this assay is not widely available.

The identification of an adrenal mass and increased aldosterone concentration in an animal with consistent clinical signs is considered sufficient to confirm the diagnosis.

Hypertension is common in humans with diabetes mellitus and is considered one of the most important co-morbidities. There are variable reports regarding the prevalence of hypertension in dogs with diabetes mellitus. Up to 50% have been shown to be hypertensive. However, associated clinical features are rarely reported. Hypertension in diabetic cats is uncommon.

References

1.  LeBlanc NL, Stepien RL, Bentley E. Ocular lesions associated with systemic hypertension in dogs: 65 cases. J Am Vet Med Assoc. 2011;238;915–921.

2.  Salesov E, Boretti FS, Sieber-Ruckstuhl NS, et al. Urinary and plasma catecholamines and metanephrines in dogs with pheochromocytoma, hypercortisolism, nonadrenal disease and in healthy dogs. J Vet Intern Med. 2015;29;597-602.