I recently had my Chiari discovered during a Brain MRI, the doctor thought I had MS because I complained of right arm and neck pain/numbness/pressure. I have a 8 mm Chiari with a syrinx and I am still combating family practioners who tell me that my 8mm is "mild" and my syrinx is typical of people in the military after a certain period of time. I have been given a large collection of medicine: Percocet, Treximet, Medorl, Naproxen, muscle relaxer...the list goes on and on. I know have fatigue, leg stiffness, left hand joint pain, memory issues and blurry vision. Yesterday I started having mild pain when I swallow but I truly do not understand why so many doctors are dismissive. I see the neurosurgeon in May so I will update everyone after that.
The 8mm is maybe "mild" on paper, but there is no hard correlation between the mm and the sevirity of symptoms. 2mm can be severe and 10mm can be cmpletely asymptomaic. The larger the herniation, the more likely it will cause some problems, but you can't say it is or it isn't symptomatic by only looking on how many mm you have. By the way, the 5mm "rule" is nowhere close to a perfect definition.
Where is your syrinx located? I recently watched a lecture about Chiari on this youtube channel which has tons of great info. The doctor said, it looks like Chiari related syrinxes are most likely to be located in cervical spine and if I remember correctly they are thick in shape, as opposed to Chiari unrelated ones that are located lower in the spine and are usually skinny.
Chiari unrelated syrinx can form due to a severe injury, disruption in csf flow, or there can be an idiopathic syringomyelia without any logical explanation.