Yep, here I am revisiting the big D issue again. Do I really have MG?

I was diagnosed, more or less, a year ago. I don't think the neurologist was willing to actually use the word "diagnosis." What he said was that myasthenia is numbers one through four on the list of possibilities. That was evidently good enough for my regular neurologist, who has been treating me for MG (with Imuran, Mestinon, and IVIg) ever since. Other tests ruled out everything else anyone could think of.

The reasons I was so hard to diagnose were: I'm seronegative; my first two SFEMGs were inconclusive (third was clearly abnormal); I don't have significant eye involvement; and my most severe, most troublesome symptom at first was weakness in my side muscles that made me tilt from side to side, from the waist up, as I walked. In the beginning, this looked like a balance problem or ataxia.

Now, a year later, I think I'm a bit more "typical." The side-to-side tilting is pretty much gone. Now I tend to fall forward from the waist up if anything upsets my stride. My legs also get weak so that I sometimes slowly collapse into a squatting position--slowly, so that it looks like I'm doing it on purpose. The weakness in my arms bothers me every day. Weakness in my neck, which makes it very tiring to hold up my head, comes and goes, a few weeks at a time. I had weakness in my fingers for about a month, but that's much improved now, too. I had trouble swallowing back in February, but not since then.

I am pretty convinced I have myasthenia. What else could it be? Are there any other similar diseases in which the muscle weakness shifts around like this? I haven't had that side-to-side tilting for months now. I no longer find myself arching my back to stop from falling backwards, either. I'm pretty strong in the morning, except on a really bad day, and weak in the late afternoons and evenings. I zip up and down the stairs in the beginning of the day, but sometimes at night my husband has to carry/drag me up to bed. I can pick up heavy things--I just can't hold them for long. My eyes are still good. Mestinon doesn't help me at all, as far as I can tell, but I can take a lot of it without much effect besides a bit of twitching. I've been on Imuran for nine months with no response. I've had three courses of IVIg: the first helped a bit, the second helped tremendously, and the third didn't help much.

So, what do you guys think? If you were me, would you be confident you had MG? Can anyone think of any other disease that behaves this way?

By the way, I have seven siblings, and seven children, and 29 nieces and nephews on my side of the family, and none of them has anything neurological going on. I'm 45, and have had symptoms, looking back, for almost three years.

Abby