Hello, I am Dr. B, a licensed veterinarian and I would like to help you with Pickle today.
Now if Pickle is losing hair on her hind quarters and has scabbing at the neck, these are all hallmarks of an itchy cat who is overgrooming. As I am sure you already know too well, the mystery of what makes a cat incessantly itch, chew, or pull out hair can be a real challenge to get to the bottom of. This is because feline itchiness and hair loss can be caused by a number of things. The most common reasons are either stress based (less likely here since she has scabbing at the neck) or allergy based. To make it even more difficult for us, allergies can be to literally anything in their kitty world. This includes food, parasites (specifically flea saliva not the fleas), pollens, and anything that they essentially come into contact with.
If she had improved when at your friends, it is a case of determining what changes may have been in place there. It may require you channeling your inner Sherlock Holmes but you want to consider what differences there are between households (food, carpet or laundry powders, flea exposure, plant exposure, etc) as this can shed light on the trigger for her allergic signs.
For example, if she had been on a different diet, then you might consider a diet trial (for 4-6 weeks) at your home with the diet she was fed. If the diet was unchanged, then we can put those type of allergies lower on our list with Pickle.
As well, it would be ideal to discuss with your friend what chemicals/powders/etc. are used in their household. It is possible that Pickle may just have an allergy to something used within the household. Furthermore, it would worth knowing if she was totally indoors at your friend's house while she was there. The reason is because if she was in more, then perhaps she was less exposed to an outside allergen that she meets regularly when outside at home. Or it is possible (though hard for us to control) that there is a particular pollen source that is high in your garden but not your friend's.
You haven't mentioned any flea control, but I would say that we do have to consider that perhaps Pickle is exposed more (especially if she goes outside and you have more local cats in your neighborhood) to them at your house. As I noted before, cats are not actually allergic to the flea. They are allergic to its saliva. So, all it takes is one flea having a nibble of her outside to start things off. The body releases histamines and the allergic response takes over. This is itchy and sore, so our cats may itch, scratch and some will even start pulling 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). So, if we are trying to be thorough in ruling out her allergic trigger, it would be worth making sure you are using a good quality monthly flea medication (ie Advantage II, Advocate, Frontline Plus, etc). I would warn that we are seeing some flea resistance to the grocery store brands and even plain Frontline; therefore we do want to make sure we are using something we know works so that we can officially ensure that her signs are not a flea allgery dermatitis.
Finally, while it is ideal to try to find the allergen and remove it from the environment, this is sometimes not possible. In those cases, where we have a cat who is itching all the time from allergies, we will often use anti-histamines like Bendryl (Diphenhydramine) to help give them some relief. (Benadryl- LINK). A low dose (ie. 0.25mg per pound of his body weight twice daily) can just be enough to break that itchiness cycle, and give her skin the chance in needs to settle. We like to keep the dose low in kitties, as they can have drowsiness with this medication (just like people). And since you are in the UK, I will especially note that you do need to make sure that any Benadryl you use has Diphenhydramine (since some of the UK preparations use other drugs). Otherwise, you can use Piriton (chlorphenamine) at a dose of 2mg (1/2 a tablet) twice daily. 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
Overall, allergic skin disease in the cat can be a big challenge to manage. That said, if her signs settled at your friend's house then this does confirm that the allergen trigger that is causing her signs is something in your environment. Therefore, with good detective work, you should be able to narrow down causes and potentially adapt your household environment to lower her allergic reactions and settle her skin.
I hope this information is helpful.
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