Today we are going to discuss two cases of cats with blood in their eyes. After veterinary investigation both were diagnosed with a rare but likely underreported disease – but that wasn’t immediately apparent.

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Let’s Meet the Cats

Arthur was an 11-year-old, male neutered DSH cat who presented to his local vet after a short history of wobbliness, bumping into things, a lack of weight gain and redness of the eye. He hadn’t been seen by his vets for a few years but had otherwise been healthy. He lived with his brother who had no problems.

Tinkerbelle is a 13-year-old female neutered DSH cat who first presented to her local vet after she became lethargic, stopped eating and had one red eye. She was seen a month earlier due to drinking excessively for at least a week, but no cause was identified. She had been seen regularly for annual vaccinations before this. 

Arthur’s Case

On examination by the vet, Arthur was underweight and ‘looked old’. Both his eyes showed hyphaemia, or blood in the front chamber of the eye. On closer examination, his retinas were detached, resulting in lack of vision. Concerned about his blood pressure, the vet used a blood pressure cuff to check – this identified hypertension (high blood pressure).

Further blood testing showed normal kidney, liver and thyroid function, but a slightly low potassium level (hypokalaemia). At this stage, treatment for hypertension of unknown origin was started with amlodipine tablets.

Tinkerbelle’s Case

On first examination, Tinkerbelle was quite lethargic and also had hyphaemia of the left eye. Her right eye was normal, and both retinas were intact; though her left pupil was large and unresponsive to light. Her left eye was blind. But she has retained vision in her right eye. Her blood pressure was high, and her potassium was also slightly low. Her kidneys appeared to be under some strain but were functioning. It was decided to also start amlodipine to try and reduce her blood pressure and protect her kidneys. 

Causes of Hypertension

Hypertension, or high blood pressure (systolic pressure above 150mmHg), is commonly seen in cats and should not be ignored. Hypertension can cause damage to organs such as: damage to the eyes (blindness, retinal detachment, bleeding); central nervous system (disorientation, seizures); kidneys (increased urination, protein loss, kidney disease); and the heart (heart disease and heart failure).

Hypertension can be primary and caused by excitement or fear, or secondary. Secondary hypertension can be caused by pain, heart disease, kidney disease, hyperadrenocorticism (although this is very rare in cats), hyperthyroidism, diabetes mellitus, hyperaldosteronism, certain drugs, and a rare cancer called phaeochromocytoma.

Maintaining normal blood pressure is critical to prevent irreversible organ damage, so treatment with drugs like amlodipine is essential. Treating any underlying disease is also important. Regular monitoring must be performed to ensure the blood pressure does not go too high or low. 

Arthur’s Complications

Arthur initially did very well on amlodipine for treatment of hypertension of unknown origin, though remained permanently blind. However, a few months later, the owner noticed he was urinating on his bedding and gazing into space again. His blood pressure was under control, but there was now evidence of kidney disease, which was likely the cause of his urination problem. His potassium had also dropped lower, to the point where it was recommended he received a potassium supplement in his food. 

The vet was quite concerned with these sudden changes, especially since his blood pressure was under control, so advised further investigation. An ultrasound of his abdomen was performed, which showed a suspected enlarged left adrenal gland. The vet recommended a special blood test to measure his aldosterone level – the result showed high aldosterone. 

Arthur’s final diagnosis was primary hyperaldosteronism, or Conn’s disease. To manage this disease, amlodipine was continued, potassium was supplemented, and his kidney disease was managed with a prescription diet. Arthur did very well on this treatment for a few months, but was sadly put to sleep later on for unrelated reasons. 

Tinkerbelle’s Outcome

For almost a year now, Tinkerbelle has been managed very well with amlodipine and potassium supplementation. Her vision remains intact in her right eye. Her kidney parameters are stable, so although her kidneys are having to work hard and are vulnerable to future damage, she currently does not have chronic kidney disease. She is on a prescription renal diet regardless, to reduce any strain on her kidneys. 

Her vet sees her every 3 months to check her blood pressure and potassium level, and every 6 months to check her kidney function. Since she is stable, her owner isn’t wanting to investigate further, so she does not have a conclusive diagnosis. However, like Arthur, Conn’s disease is likely. 

Conn’s Disease

Normal Aldosterone Function

Primary hyperaldosteronism, or Conn’s disease, is a disease caused by a tumour of the adrenal glands. The adrenal glands are little organs situated on top of each kidney. They have many functions, including production of aldosterone. 

When the kidneys detect reduced blood flow, they release hormones that stimulate the release of aldosterone.  Aldosterone acts on the kidneys, causing them to absorb more sodium and less potassium from the urine – this causes more water to be reabsorbed into the bloodstream, raising blood pressure. In short, aldosterone release raises blood pressure.

Hyperaldosteronism 

Normally this system works in balance to maintain normal blood pressure. However, sometimes the aldosterone-producing tissue of the adrenal gland can become cancerous, resulting in uncontrolled overproduction of aldosterone. This ultimately leads to high blood pressure and low potassium. 

The symptoms of Conn’s disease are primarily associated with hypertension, and both Arthur and Tinkerbelle showed some of them. Other common symptoms are generalised weakness, lethargy, muscle wastage and neck weakness due to low potassium.

Diagnosis of Conn’s Disease

Diagnosing Conn’s disease can be difficult. To start, a full clinical exam should be performed to identify symptoms of hypertension, such as blindness or blood in the anterior chamber, like both Arthur and Tinkerbelle had. Blood pressure should always be measured when this is seen – note that blood pressure can sometimes be normal in some cases of Conn’s disease. 

Full blood testing should next be performed. This can identify other causes of hypertension, such as hyperthyroidism, as well as any potential damage. Kidney disease is often seen, and because kidney disease can cause hypertension it is often the presumed diagnosis. But remember that kidney disease may be a symptom of hypertension, not necessarily the cause. Other changes may include alkalosis (low blood pH), high creatine kinase due to muscle breakdown, and anaemia due to kidney disease. Low potassium is often seen, but not always. Sodium is usually normal. Urine testing can confirm if there is kidney disease.

This information is often enough to start treatment, but further investigation may be necessary to confirm the diagnosis. Imaging the adrenal glands via ultrasonography, CT or MRI may reveal a unilateral enlarged adrenal gland. This can be sampled to confirm the presence of a tumour. Advanced blood tests can be performed to identify high aldosterone, low renin, and high aldosterone-renin ratios. A cat can also be injected with the drug fludrocortisone – if the aldosterone level fails to reduce in response, hyperaldosteronism is likely. 

Cost issues

These tests can be expensive, and although sometimes a presumptive diagnosis is sufficient, it is often best to be sure what the condition is before starting treatment.  

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Treating Conn’s Disease

The priority for the treatment of Conn’s disease is increasing blood potassium and reducing blood pressure.

If the potassium is dangerously low (<3mmol/l), it can lead to collapse, heart failure and even death. In these cases, intravenous potassium should be supplemented until the levels are normal. Once normal, these can be maintained in the long-term with an oral potassium supplement. The drug spironolactone can also help as it inhibits aldosterone. 

Management of clinical hypertension requires anti-hypertensive drugs such as amlodipine. ACE-inhibitor drugs are not effective, as the renin they act upon will generally be low anyway. Caution must be used to avoid hypotension (low blood pressure). 

It is also important to manage blindness, kidney disease, heart disease and any other secondary disease. Kidney disease in particular should be addressed, as if left unchecked it can worsen hypertension. 

The only permanent treatment for Conn’s disease is surgical removal of the enlarged adrenal gland. This is a complex procedure and not without risk, but it can have a positive outcome if surgery is successful. It is only practical in cases where the mass has not already spread to other parts of the body (metastasised).

Prognosis

For many animals, medication alone is enough to stabilise the condition and improve their quality of life. Since Conn’s disease is caused by a tumour, the tumour may grow over time, and medication may need to be adjusted. Regular check-ups with a vet are crucial.

Ultimately, the outcome depends on how quickly the disease is diagnosed and how much damage to organs has already been done. If too much damage has occurred and the cat’s quality of life is reduced, euthanasia on welfare grounds is a sensible option. The long-term outlook for patients who are stable is unknown, given how little information there is on this strange disease. 

Further Reading