Our surgeon considers Marfans-associated scoliosis as AIS. Others on the group have been told Chiari/SM is also considered AIS.

In both these cases, it has been shown that they differ in some important aspect from the great run of AIS. For example, if you take the topic of bracing in Marfans, we can find the following in the referred literature (recall normal caveats about this):

Physicians should understand that most patients with Marfan syndrome who have a curve of more than 25 and a Risser sign of 2 or less will reach the surgical range, even with brace treatment.
Now that is certainly NOT the case with straight AIS where bracing certainly has NOT been universally disproven. Also some straight AIS curves stop on their own, even at high angles, and apparently that is not the case in Marfans. So lumping Marfans in with AIS results in a false conclusion that bracing has been disproven in AIS and that AIS curves never stop on their own at any angle.

W.R.T. Chiari/SM, it is my understanding that instant reductions in structural curves without touching the vertebra as in fusion, stabling, tethering, etc. can occur with draining the syrinx. There is no similar phenomenon of instant reduction to my knowledge in straight AIS. So lumping Chiari/SM in with AIS results in the false conclusion that instant reductions in structural curves without touching the vertebra occur in AIS.

What am I missing? This is certainly not my field but logic still applies.