Hi Maggi, well I am seronegative GMG & have (last checked a 4 mm cerebellar tonsillar ectopia, 5 is what most DR. go by for CM, that are not top Chiari Specialist. But size O Chiari is controversial just like seronegative MG) when it was first found noted too small to measure, so it is growing. And yes, I have symptoms for Chiari that do not go with MG. I personally know 4 people that have had surgery for their Chiari (no MG). These are not just found at autopsy they just are not told to people that have them. Even if the brain is very herniated into the spinal column. I have a 2 Dr's confirm mine is an Arnold Chiari even at 4 mm with no treatment suggested. 1 of these is my current MG specialist but he is not a Chiari specialist. Sending this link to you also about Chiari... I have many of the Chiari Comorbidities also that are list on this site...... Hugs and Best wishes!! ❄️Sally Farrier...Myasthenia-Gravis.com (team member). https://chiaribridges.org/