It's unclear whether or not ALS (any form) is an autoimmune disease.
Autoimmune diseases are typically associated with autoantibody production. These are in evidence in (-- at least some forms of --) ALS, but in an unusual way that makes their role highly uncertain. They are potentially beneficial. See:
https://pubmed.ncbi.nlm.nih.gov/25344935/
What's the common factor - are they all autoimmune diseases?
Would the "inverse vaccine" approach discussed here recently help?