Hi SLS,
I know this is frustrating.  It sounds as if the areas where you are losing your muscle strength is also where you are experiencing atrophy.  That is probably because you are not using those muscles as much as you once did, and atrophy occurs naturally as we age.  I have the same problem with my legs and even my toes!

Recommended treatment includes moist heat and whirlpools, but the heat makes our MS worse.  Of course exercise is a treatment, but it is so difficult to move actively which is why we have the problem in the first place.  I am sorry I could not find many tips in this area. 

My occupational therapist did recommend some exercise activities with my hands.  Perhaps your doctor could arrange a therapist to provide specific recommendations.
This is particularly frustrating for those of us who were very energetic at one time.  Please let me know how you are doing.  Good luck.