Hand cramps happen in MG when the disease is worse or you have used the hands a lot. I agree. Check with your neuro.

Locking up of fingers can be "trigger finger." That is treated with a steroid shot and therapy or finger devices. An orthopedic clinic can help with that.

If you are concerned about potassium or magnesium levels, better to be tested first to see. Too much or too little of those can cause MG to become worse. FYI

Annie