Hi, nice to meet you ! I am new here & just read your post & thought I should respond. I have been diagnosed with MG for just about a month now & have had muscle pain (no knots tho) for years and was not on any medicine until now, which is mestinon (making me sick tho) which is prescribed specifically for MG & if it is working that good for you, I would be thinking that is likely what you have, plus your symptoms sound dead on to MG . Is it a deep muscle pain? Mine is and is in my upper thighs, lower calves, arms not so bad; but for sure a bad pain that lets you know it is there, like I ran a hundred miles non-stop. Plus it being a rare disease, they simply might not know that it DOES cause pain in some of us. I looked up the very same thing because I happened to read it "doesn't cause muscle pain" & was shocked. I looked on other sights & some did complain with having muscle pain. Have they done a muscle biopsy on you? That is the only way they found mine after nearly 15 or more years of suffering. And now I can't seem to be able to take any of the medicines that even help. I feel like it was all a waste of time and money. But yes, I would concur it most certainly causes muscle pain, at least for me and some of us from the sounds of it. It is probably not called the Snow-Flake disease for not, it makes each of us feel and re-act differently to the disease.

Hi me again! Here is an interesting site on pain & MG.https://www.drugs.com/answers/myasthenia-gravis-i-was-diagnosed-with-mg-approx-251914.html. I thought this might help you.

Am wondering how a muscle biopsy diagnosed MG? I have never heard of that. I was tested for two antibodies and had EMGs - all negative. I have seen multiple neuros - most just once... because once one test is negative it seems no follow up is needed. One neuro I saw in 5/16 suggested a muscle biopsy but referred me to a larger practice. But they just did an EMG and sent me on my way. My pain is a deep muscle pain that increases with use. Usually my neck and arms - just from being upright and using my arms. But my legs too if I walk a lot. Before mestinon my diaphram used to ache - i guess just from breathing. I do have a history of chronic pain but it was different and caused by spine issues.

I am not sure, but this is what I found on the web on muscle biopsies:

Why might I need a muscle biopsy?
You may need a muscle biopsy to assess your musculoskeletal system for abnormalities. Various disease processes can cause muscle weakness or pain. These conditions may be related to problems with your nervous system, connective tissue, vascular system, or musculoskeletal system.

A muscle biopsy helps determine the source of the disease process. This ensures the proper treatment.

Your doctor may do a muscle biopsy diagnose neuromuscular disorders, infections that affect your muscle, and other abnormalities in your muscle tissue. These are some conditions diagnosed by muscle biopsy:

Muscular dystrophy (MD). A broad term that describes a genetic (inherited) disorder of the muscles. Muscular dystrophy affects skeletal muscles and other organ systems. When the muscles break down, fatty deposits replace them over time. There are many different types of muscular dystrophy.
Duchenne muscular dystrophy (DMD). The most common form of muscular dystrophy. DMD usually affects only males.
Becker muscular dystrophy. Similar to Duchenne muscular dystrophy (DMD), but usually more mild and symptoms start later in life.
Trichinosis. An infection caused by a parasite that lives in raw meat. Symptoms may include muscle pain.
Toxoplasmosis. An infection caused by a parasite that invades the tissue and can damage the central nervous system, especially in infants.
Myasthenia gravis (MG). A complex, autoimmune disorder in which antibodies destroy neuromuscular connections. This causes problems with the nerves that communicate with muscles. MG affects the voluntary muscles of the body, especially your eyes, mouth, throat, and limbs.
Polymyositis. A chronic disease involving skeletal muscles.
Dermatomyositis. A collagen disorder that causes inflammation to the skin, muscles, and subcutaneous tissue, often resulting in weakened muscles.
Amyotrophic lateral sclerosis (ALS). Also known as Lou Gehrig disease, ALS is a disease that attacks the nerves signaling voluntary muscle movement, eventually causing paralysis.
Friedreich ataxia. An inherited, genetic disorder that involves balance and coordination.
There may be other reasons for your healthcare provider to recommend a muscle biopsy.

Let me read thru my muscle biopsy report & see if I can find how they diagnosed it thru a muscle biopsy. They put me on Mestinon & it is making me very sick at the moment & he wants me to take a medicine that one should not take if you have had cancer & I had breast cancer & a left breat mastectomy last year; so I am terrified to take that one. I am really sick & depressed at the moment.

Great post Meng -- yes, a lot of us do have pain from our MG, usually because we are straining to hold our heads up. For me, the first symptoms were in my feet and ankles. I've always had weak ankles, but they started to really deteriorate about a month before the double vision started. Now they ache all the time, especially during humid days. Today is dry, and my ankles feel great. Odd how this disease is sometimes. ~joe

Absolutely it completely makes sense our muscles would hurt because they are weak and we are straining them. I often had muscle pain especially before i was on routine mestinon. Ive had symptoms for few years still no exact diagnoses but I'm on the 6th neurologist and this one listens and believes it is MG even with seronegative results. Just keep going to new neurologist until you find one that listens.

I think you definitely need to take more Mestinon. My Rx is 60mg every 4 hours.