http://tinyurl.com/ds2lz
How is polymyalgia rheumatica treated?

The treatment of polymyalgia rheumatica is directed toward reducing
inflammation. While some patients with mild symptoms can improve with
nonsteroid antiinflammatory drugs, such as aspirin or ibuprofen (Motrin,
Advil), most patients respond best to low doses of cortisone medications,
such as prednisone or prednisolone. Not infrequently, a single day's
cortisone medication eases many of the symptoms! In fact, the rapid,
gratifying results with low dose cortisone medications is characteristic of
polymyalgia rheumatica.
The dose of prednisone is gradually reduced while the doctor monitors the
symptoms and normalization of the blood ESR. Reactivation of symptoms can
require periodic adjustments in the prednisone dosage. Most patients are
able to completely wean from prednisone within several years. Some patients
require longer term treatment. Occasionally, patients have a recurrence
years after the symptoms have resolved. The ideal prednisone dosing regimen
continues to be sought by researchers.

***** My .02
MTX is a cytotoxic drug so I'm including that info.
If I had PMR, I would not take MTX for it.  I'd want a muscle relaxer, a
pain medication that covered my pain and an anti-inflammatory.  I looked at
several sites and none mentioned using dmards for PMR.  Is that all your
mother has?  Could she have RA or another autoimmune disease?
Your mother should not be suffering.  Find a doctor who will treat her pain.
You can have 2 separate doctors... one for pain and one for PMR.  Some
doctors are scared of pain meds or just plain ignorant.

Here's the answer re: the anti-cancer drugs
What are cytotoxics?
Cytotoxic or immunosuppressive drugs suppress immune function.  They can
suppress any arm of the immune system, like T cells or B cells, they can
suppress transplanted organ rejection, the making of antibodies, or the
attack of certain cells, viruses or tumours.  The use of cytotoxic drugs is
called chemotherapy.
Cytotoxics kill or inhibit the action of the immune system.  This can result
in death of cells or the interruption of the synthesis of antibody.  Certain
cells of the immune system manufacture antibodies, so if we turn off the
manufacture of the antibodies, the damage done to the body, as a result of
immune complexes, ceases.

What cytotoxics are used to treat lupus?
Cyclophosphamide (Cytoxan) - best used intravenously.
Chlorambucil (Leukeran) - much better tolerated than oral Cytoxan, long term
use (more than 2 years) makes it a potent carcinogen.
Azathioprine (Imuran) - has modest effects on serious lupus, but has the
advantage of reducing steroid requirements.
Methotrexate (Rheumatrex) - works within weeks, & is taken only once a week.
Decreases joint inflammation, but can make lupus patients more sensitive to
ultraviolet light.  Has little effect on organ-threatening disease. Must be
used carefully in patients with kidney impairment.

What symptoms of lupus can cytotoxics be used to treat?
Cytotoxics are very strong drugs, & usually only used to treat lupus when
absolutely necessary.  They are used on patients who have major organ
involvement, severe muscle inflammation, or intractable arthritis.
What are the side effects of cytotoxics?
Cyclophosphamide - hair loss, nausea, vomiting, possible infertility, can
result in the cessation of bone marrow function, resulting in anaemia, & low
levels of white blood cells & platelets.
Chlorambucil - occasional skin rashes, nausea, vomiting, diarrhoea, bone
marrow suppression(as with cyclophosphamide), increased production of
fibrous tissue in the lungs is a rare but serious problem.
Azathioprine - skin rashes, diarrhoea, nausea, vomiting(occasionally),
occasionally results in cessation of bone marrow function (as with
cyclophosphamide).
Methotrexate - nausea, vomiting, diarrhoea, anaemia, bone marrow
suppression(as with cyclophosphamide), liver damage.