Hypertension (high blood pressure) affects up to 20% of cats with kidney disease and 25% of cats with hyperthyroidism. It is called the "silent killer" because it causes progressive organ damage -- particularly to the eyes, brain, heart, and kidneys -- often without obvious symptoms until a crisis occurs.
Causes
- Secondary to kidney disease: The most common cause (~65% of cases)
- Secondary to hyperthyroidism: ~25% of hyperthyroid cats develop hypertension
- Idiopathic (primary): No underlying cause found (~15-20%)
- Other: Pheochromocytoma (adrenal tumor), hyperaldosteronism (rare)
Target Organ Damage
| Organ | Damage | Symptoms |
|---|---|---|
| Eyes | Retinal detachment, bleeding | Sudden blindness, dilated pupils (most common presentation) |
| Brain | Hemorrhage, edema | Seizures, disorientation, head tilt, circling |
| Heart | Left ventricular hypertrophy | Heart murmur, eventually heart failure |
| Kidneys | Accelerated kidney damage | Worsening CKD values, protein in urine |
Diagnosis
- Doppler blood pressure measurement: Most common method in cats
- Normal: Systolic below 140 mmHg
- Pre-hypertensive: 140-159 mmHg (monitor closely)
- Hypertensive: 160-179 mmHg (treat, low organ damage risk)
- Severely hypertensive: 180+ mmHg (treat urgently, high organ damage risk)
- Multiple measurements needed (stress can artificially elevate BP in cats)
Treatment
- Amlodipine (Norvasc): First-line treatment -- calcium channel blocker. Very effective in cats.
- Starting dose: typically 0.625mg (1/4 of 2.5mg tablet) once daily
- Recheck blood pressure in 1-2 weeks, adjust dose as needed
- Most cats achieve good control with amlodipine alone
- Treat underlying cause: Manage kidney disease, treat hyperthyroidism
Monitoring
- Blood pressure check every 3-6 months for at-risk cats (CKD, hyperthyroid)
- Fundic exam (eye exam) to check for retinal changes
- If on treatment: recheck BP 1-2 weeks after dose changes, then every 3-6 months
Frequently Asked Questions
Can a cat recover vision after hypertensive blindness?
Partial recovery is possible if blood pressure is controlled within 24-48 hours of retinal detachment. The sooner treatment begins, the better the chance. Complete retinal detachment lasting more than a few days is usually permanent. This is why screening blood pressure in senior cats and cats with kidney disease is so important -- catching hypertension before it damages the eyes prevents this devastating complication. Blind cats can live excellent quality lives, but prevention is always preferred.
