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.
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.