Re: what is the difference between myotonic dystrophy and congenita please
Peter, that's good news that you have myotonia congenita and not myotonic muscular dystropny. MMD is progressive and involves many systems and organs including the heart, liver and GI tract. The only thing we have in common with it is the stiffness of the muscles.
The usual dose for myotonia congenita seems to be 200-300 mg of mexiletine three times a day. But you do need to have your heart monitored closely. Depending on your particular mutation or mutations, you may respond better to another medication like Diamox, Dilantin or Quinine Sulfate.
If you have some symptoms of fast heart rate you might want to cut out all foods containing caffeine like coffee, tea, soft drinks with caffeine, etc. That can make a big difference. Adrenaline makes myotonia much worse which is why stress affects us.
Did you get your testing at Dr. Lehmann-Horn's lab in Ulm?
Re: what is the difference between myotonic dystrophy and congenita please
Peter, are you sure it wasn't paramyotonia congenita? That is a different ion channel disorder and can cause more weakness. It could also explain why the mexiletine isn't affecting you much.
Myotonia congenita is usually fairly symmetrical, so if you did feel some weakness, it would probably be pretty equal on both sides. Were you ever in an accident that injured your back? That would be a more likely reason for you to have the weakness in one leg. Also lesions in your brain or spine from viral infections in the past can do that. If you haven't already done so, I would ask your neurologist to do an MRI to see if there are some herniated discs that might be causing the problem.