I'm a Zyrtec enthusiast too. It does not completely remove itching, but mine would be very bad if I didn't take it, because it's a common symptom of another disease, Polycythemia Vera. I take one time release Zyrtec, generic of course, every night. The non-generic is way too expensive, and I do fine with the generic. I am so profoundly grateful for my pcp for looking this up on the internet to find me an anti-histimine I can take even though i also have Porphyria. I had thought there were no anti-histimines I could tolerate. It does not make me sleepy.
People with PV also get itch from the shower, but I am atypical and I do not get itch from the shower.
I also use a humidifier on dry days, at night, one I got from the Gaiam catalog, which has silver in it to stop mold forming the the water. This also helps dry-skin itch. I use Earth Sciences body lotion to help with dryness as well. I use the Earth Sciences body lotion with SPF 15 so it does double duty.
Hope you quell the itch. i didn't know it was an MS thing. I never had it before my PV diagnosis, although I had dry skin all my life.