A decent number of people are asking why their cat is shaking his/her back legs when walking. I’d like to try and answer this question because I have seen this myself with my cat. My late lady cat did it occasionally and on every occasion it was because there was something on her paw that probably irritated her slightly.
Or, she was simply irritated and this emotion was expressed by shaking her hind leg. I have also seen my current cat do this when he has had enough food and wants to stop. On this ocassions it is body language saying ‘I’ve had enough of that’.
So, for example she may have stepped in some water which annoyed her or something else; it could be anything or nothing – perhaps she didn’t like the food offered. Something may have become lodged in between her toes for example. Therefore, perhaps the most obvious and most common reasons why a cat shakes her back leg or legs is because (a) she has stepped into something or something is stuck to her leg or paw or (b) it is body language saying ‘that’s enough’ while walking away. These are the innocent, non-health related reasons and probably accounts for 95% of the cases.
What about the potential health reasons for this? It seems to me that the most likely reason would be neurological. You could argue that 90% of the time the cause will be to do with the nerves which control the leg muscles of the cat. When we talk of neurological problems which results in what could be described as twitching, poisoning comes readily to my mind.
So, for example, an adverse reaction to an insecticide in one of the commercial flea and tick treatments may cause a cat to twitch her ears or flick her paws (paw flicking). This is considered a mild reaction by a cat who is sensitive to pyrethroids. The domestic cat is sensitive to this toxic insecticide. A flea treatment spot-on product may cause such a reaction including vomiting, diarrhea and mild depression together with perhaps salivation.
On another cat website a contributor states that she gave her cat flea drops and in the morning she noted that her cat was shaking her back leg and then a little later shaking both legs and then later than that she seemed to be shaking all over. This appears to be a neurological disorder linked directly to the application of flea treatment.
Some cat owners may describe tremors in the legs of a cat as a cat shaking her legs. Leg tremors are involuntary and the movements are repetitive. There are many possible causes one of which is a nervous system disease or ingesting something toxic which is a poisoning. Another cause is, therefore, a side-effect to certain drugs. A tremor may also be a symptom of kidney failure. Or the tremors may be a result of injury causing nerve damage.
In addition, it may be caused by inflammation which I would suggest might affect the nerves in the cat’s legs. Another possible cause might be low levels of glucose in the blood which is hypoglycaemia.
Other causes as suggested by cat owners but not vets are: A tick carrying disease called ehrlichia, an anxiety disorder, a pinched nerve or dietary deficiencies (convert to raw food diet but be careful).
If a cat has been shaking her legs all her life and she is a young cat then we could probably conclude that she has a congenital condition meaning that it is an inherited health condition.
I hope this helps. The most likely causes have been specified.