I do hope it is something that can be quickly sorted.
This is of course one of the problems with SM, the symptoms are also those of many much less serious problems.
I would agree that shampooing with malaseb would be a good first step. It may solve the itch, and your worries.
I think the advice to insure your cavalier, if you have not already done so, is one that should be taken on board by everyone buying a cavalier
Cavaliers......Faith, The Ginger Tank and Woody.
Japanese Chins.... Dandy, Benny, Bridgette and Hana.
Remembered with love......... Tommy Tuppence and Fonzi