Positive Antibodies Normal SFEMG, Dr says this rules out MG
 

Hello! I'm hoping for some input here before I go back to the neuromuscular doctor next week. It's a long story but here's the short version! I've been going back and forth to the Cleveland Clinic since Nov. after some really weird things happened to me in June 2018. They've diagnosed me with POTS after extensive testing (an autonomic nervous system dysfunction) but in the process of seeing a neuromuscular dr, he happened to test me for Lambert Eaton Syndrome. That blood test also tested for MG which came back for positive MG antibodies (ACh Receptor Bind Ab). The lab stated this in the interpretation: This antibody profile, in an appropriate clinical and electrophysiological context, is consistent with autoimmune myasthenia gravis. The dr was quite surprised and said I didn't present for that and that's not what I had seen him for and so I sent him messages thru MyChart explaining symptoms that I felt did relate that he was not aware of. He did go ahead and order a single fiber EMG which I had about 3 weeks ago at the Cleveland Clinic. It was normal and he says this now rules out MG. I have repeatedly questioned why then would I have positive antibodies. Anyway, I've since read that people can have positive antibodies and a normal EMG and a normal SFEMG and still be diagnosed with MG and/or respond well to treatment. I see this dr again on 6/27 (my 6th trip up there). Does anyone here have any thoughts on this situation and having positive antibodies? I'm terribly afraid that this is going to be missed. Why would I have the positive antibodies? I feel that I have most all the symptoms as well. When I first read about MG, it was like I was reading about myself. Thank you in advance for any help and information anyone could provide.

Hi Smirleygirl

Welcome to NeuroTalk :).

Elevated levels of anti-AChR antibodies are usually strongly diagnostic of MG.

However elevated levels of these antibodies can also occur in people with Lambert Eaton Syndrome; this is a "false-positive" result as far as diagnosis of MG is concerned. These antibodies are not associated with POTS.

Maybe this is what applies to you.

Best wishes.

Hi, thank you for the response. The Lambert Eaton blood tests were negative. The lab's interpretation stated that the positive antibodies were consistent with myasthenia gravis.

2nd opinion
 

Are you able to get a second opinion from a different neurologist not affiliated with the current neurologist? Especially one that “specializes” in MG, and has a good number of MG patients.

It’s my understanding that positive ACHR means you tested positive for MG. The quantitative number result does not indicate the severity of the disease, just that you tested positive for it.

Lisa

Hi, thank you for your input. Yes, I guess that's what I'm going to have to do if the doctor argues against MG at my appt next week. Sadly, this was all at the Cleveland Clinic in their neuromuscular dept so you would think it would be top notch. He's saying that with the normal SFEMG, I don't have it even though I have positive antibodies and symptoms and he's the one who ordered the blood test! I just wanted to confirm that my thought process was correct that positive means positive!

There are also a few things that can cause a false negative on the sfemg - it relies heavily on the technician's skill and experience, and with MG, the muscles will perform more normally if they're cold. I can't find the study but the difference of a few degrees cooler can easily tip you from positive to negative. Also maybe it was just a good day for you or they tested the wrong muscles.

I hope the appointment went well