I;ve heard visas can be applied for and granted to those with certain medical conditions, asthmatics, arthritics etc, unable to endure cold climates. Is this so? Would help my mother who suffers from arthritis. And where's the list. Thanks.

If your mom is 50+ she can simply apply for a non-O visa (retirement visa)

I have never heard of a medical visa myself.

Although there is a visa available for medical treatment (non immigrant O) believe you are talking about the old retirement provisions from several decades ago when normal retirement age was 60 and special provisions were available. When change was made to age 50 believe they were removed (although can not recall the exact provisions).

sounds more like extension of visa for medical reasons......visa 'cus can't handle cold weather .........

As has been stated, those provisions are gone. Instead is now the regular visa and extension of stay based on retirement, for which one needs to be over 50.

If she is 50+ years old and has a pension of 65,000 baht a onth or 800,000 baht in a bank account she can apply for a non-O visa and ghet yearly extensions of stay.

If she wants to stay here for medical reasons, do check what the consequences will be for her medical insurence. A new insurence in Thailand will almost certainly mean that any existing condition will not be covered. That means she might need to pay for herself for any help that she requires.