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Mrs H
by Di Rees BVetMed MRCVS

(A hyperthyroid cat having a hypokalaemic crisis)

A couple of weeks ago, my own cat, Mrs H, had to be admitted to our Nailsea practice for emergency treatment.

I acquired Mrs H 8 years ago.  She was a stray adult cat who was living rough on a trading estate.   She soon made herself at home with me, and is a very home-loving and affectionate cat.

She was diagnosed with hyperthyroidism about three years ago.  This is a common condition which affects older cats and is normally caused by a benign growth in the thyroid gland. As a result of this, extra thyroid hormone is produced.  Common signs of hyperthyroidism are:

     - Increased appetite
     - Weight loss
     - Increased thirst
     - Increased heart rate
     - Diarrhoea
     - Behavioural changes such as restlessness or agitation.

Treatment is in the form of tablets (for the rest of the cat’s life), or in some cases the over-active gland can be removed surgically once the level of thyroid hormone has been brought down to normal levels with tablets. 

Mrs H responded to well to oral treatment.  We monitored her weight and heart rate as well as routine blood samples to check her thyroid levels were normal.

Mrs H had been doing extremely well until I got up one morning to find that she had been sick overnight.  I couldn’t find any obvious abnormalities when I examined her, so I assumed that she had a stomach upset.  I did not offer her any food that day in order to rest her digestive tract and allow it to recover.

The following day I was relieved to see that she hadn’t produced any more vomit, so I offered her a small amount of chicken.  However, it was quite clear that she was not at all interested in this and more worryingly, she was obviously becoming quite weak.

The veterinary nurses took a blood sample from her jugular vein, and some tests were quickly run on our in-house analyser.  The tests revealed that the levels of potassium in her blood were dangerously low.

Potassium is a mineral which has to be kept within certain levels in the blood-stream. Either too much or too little can be life-threatening.  We needed to restore her level to normal quickly and safely.  We set up an intravenous drip of saline, to which was added a carefully calculated dose of potassium chloride.  This was administered via an infusion pump at a set rate over a period of 12 hours.

Fortunately Mrs H responded extremely well to her drip.  Within a few hours was looking noticeably stronger and had started to eat some freshly-cooked chicken. I took her home later that evening, and since then I am very pleased to be able to say that she hasn’t looked back. However, in future I will need to monitor her potassium levels as well as her thyroid levels.

Hypokalaemia is the term used to describe low levels of potassium in the blood-stream.  There are several conditions which can increase the risk of this condition occurring for example kidney disease, vomiting and diarrhoea, and hyperthyroidism.  Signs of Hypokalaemia are:

     - Lethargy
     - Muscle pain
     - Muscle weakness
     - Crouched gait
     - Neck is flexed downwards.

The condition can be life-threatening if it causes weakness of the respiratory muscles so prompt diagnosis and treatment is vital. 

As the condition is normally secondary to an underlying disease process we must always try to find out why a particular animal has become hypokalaemic.  In Mrs H’s case, it was probably related to her over-active thyroid problem.

Most affected animals will need to continue with some sort of potassium supplement to reduce the risk of another crisis at some point in the future.  This can be in the form of tablets or medicine. Prescription diets for cats with kidney problems can be very useful as they contain higher levels of potassium than normal cat food.

Mrs H now enjoys Hills feline k/d diet and has to put up with having two potassium tablets daily, in addition to her daily anti-thyroid medication.  I try to tell her that it’s all for her own good, but I don’t think she believes me!