Thank you again,
Now as I am sure you are aware, the mystery of what makes a cat have incessantly itchy skin can be a real challenge to get to the bottom of. It is because itchiness and hair pulling in cats can be caused by a number of things (just as it can with people).
The most common triggers for these conditions are either stress based or allergy based. In Cat's case if there have been no changes to his environment and you are seeing him do this, then traditional externally induced anxiety is less likely here. Still, especially since he is older, we do have to keep in mind that we can see this as a secondary sign in cats with internal issues (ie hormonal diseases like hyperthyroidism among others). Therefore, you do want to keep a wee eye out for any increases in his thirst, urination, or change in appetite. I am glad that he has a good appetite, but I would also say we need to make sure it is one that isn't overly voracious (since issues like diabetes or hyperthyroidism will make them overly hungry) and that he is either gaining or maintaining weight appropriately to what he is eating. If there is any doubt on that, then it'd be prudent to consider following up with his vet about a potential geriatric blood screen to make sure the coat/skin signs are a mild early stage hint of something brewing.
Otherwise, in Cat's case, we'd need to be thinking about skin irritation due to allergies. And just like in people, allergies can be to literally anything in their kitty world. This includes food, parasites (like fleas), pollens, and anything that they essentially come into contact with.
Now with your additional history, if there has been no diet additions in the past 2 months or so, then hopefully dietary allergies can be ruled out here. As well, if he is targeting his back/flanks, rather then belly, tail, or feet; this makes contact allergies (ie to laundry or carpet powders less likely). Therefore, we'd need to consider environmental allergies (pollen and flea saliva).
Environmental allergies can arise due to a range of agents. They can be caused by particular pollens and therefore be seasonal. Other cats can show skin reactions of the nature to indoor allergens like dust mites. Furthermore, while you do regularly treat him for fleas, his target areas suggest that we cannot completely rule a flea bite out in his case This is because the hair pulling areas actually suggest that the irritant is affecting these locations specifically; as opposed to a diffuse food allergy that would make a cat itch everywhere such that they they'd just go for the easy to reach places like the belly or tail.
In that case, fleas can act as a focal irritants. And the problem with wee kitties with sensitivities to fleas that they aren't allergic to the fleas themselves. They are allergic to its saliva. So, all it takes is one flea having a nibble to start things off (it could have even bit him and died from the Frontline but still have left its saliva to cause the irritation). The body releases histamines and the allergic response takes over. This is itchy and sore, so our cats may itch, scratch and pull out tufts of hair. They scratch which can irritate the skin even more, and its a vicious cycle (they itch b/c its itchy, but its itchier because they itched, if you know what I mean). As well, as they are causing damage to the skin from scratching, they will open the door for bacterial infection (which makes it even itchier). If it is flea saliva induced, the flea that may have bitten him to start off the last cycle is probably long since dead. Now cats caught in this kind of allergic response often respond well to religious monthly flea treatment but sometimes they need additional short term medications to help break the itchiness cycle.
Therefore, in his case, you can try to soothe the itch and at the same time rule out allergic skin disease (flea saliva induced or environmental allergen), by treating him with an anti-histamine. Anti-histamines can settle allergic skin reactions in early stages or mild cases since the skin irritation is an allergic response. Typically in these cases, we will use Piriton for these wee ones (ie 2-4mg or 1/2 - 1 tablet of a 4mg Piriton tablet up to twice daily). Do note that while anti-histamines will break that itchiness cycle and give his skin the chance it needs to settle, it can make kitties drowsy. Therefore, we always keep the dose low and if he were to be drowsy on this, then we'd reduce the dose to once daily for him. And of course, this medication shouldn't be used if your kitty has any pre-existing conditions or are on any other medication without speaking to your vet. That all said, if you treat him with this and he doesn't settle or his irritation is very severe, then he may require a short course of a steroids to allay the allergic skin response and associated itchiness.
Overall, his signs suggest a more focal skin irritation rather then one affecting the whole body. No matter if the trigger is a pollen or incidental inoculation with flea saliva, your approach here needs to be to settle the irritation for him. Therefore, do consider using antihistamines at this stage. If he is willing to be bathed (though most cats aren't), you can also consider using an emollient shampoo ((ie Episoothe, or oatmeal based ones) to soothe his skin. If he continues to pull hair, then you may also have to consider using a buster collar or baby t-shirt (with an elasticated waist) to protect his skin. And if you are seeing any increase in thirst, urination or a lack of weight gain to match his appetite; then we do have to also consider internal health issues may be causing his hair pulling as a side effect. So, do try the above but do also monitor cat closely at this stage.
I hope this information is helpful.
If you need any additional information, do not hesitate to ask!
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