Sorry to pry, but may I ask which neuro-muscular disease you're referring to? A bit fascinated by the inability of many doctors to make proper diagnoses when dealing with neurological issues.
No worries. It's no big secret for me. Most people don't know what it is; I even got a blank stare from an ER doctor once when I was taken in during an extremely bad episode.
It is extremely rare and occurs in only about 1 in 1 million people.
https://en.m.wikipedia.org/wiki/Stiff_person_syndrome
For this particular illness, 6 years is the average amount of time it takes to diagnose. Just to help put it in perspective.