How To Treat Severe Itchy Arms And Legs?

My 101 year old mother is suffering from extreme itching on her arms, legs (especially shins and ankles where a red rash appears). She especially experiences this extreme itching at night and in bed at the nursing home. She has been prescribed a topical steroid cream along with cetaphil, takes claitan in the am and must have both 50 mg of benedryl and zanax at night if she is screaming for help (not every night). She is on seroquel (12/5 mg. 3 x day) and medicaine for gout and high blood pressure --to many to name at this point. She has dementia (for which she was prescribed the seroquel this past winter). She has seen a dermatoligist and recently her primary care doc ordered blood tests to see what might be going on. She's had skin itching for several years, but this is very bad. At one time when she was in the ASstd. Living unit, they suspected scabies, but ruled that out. Several years ago she had a bad case of poison ivy.
Any suggestions will be helpful.
thank you.