How to get PEX for PANS kiddo with weird autoimmunity? (and request for sympathy)

[wisdom_seeker]

TLDR:  What auto-antibodies have you seen in PANS kids that insurance didn't dismiss? 
            We'd like a list of antibody tests or other evidence that can help get PEX authorized for a non-PANDAS kid.

Details:

My DS20 is pretty disabled due to MCAS and PANS symptoms, and his MD really wants to reboot his immune system due to his very high levels of auto-antibodies and dysregulated immune system.  Because of his persistent high mycotoxins and persistently high IgEs, treatment with PEX --> IVIG + Rituximab makes more sense than IVIG -> Rituximab to us and at least some of his MDs. 

The problem is how to demonstrate medical necessity to insurance, since he's not at death's door, and doesn't have PANDAS. The autoantibodies found so far (some at 4-14x upper threshold) aren't the old "standard" ones, and he has very high IgE (1200-2300),  so his MDs are guessing he's got other autoantibodies as well. 

I'd like to get him thoroughly tested for auto-antibodies before we reduce his IgGs more with steroids or invalidate tests by doing IVIG.   So what tests have you found useful?

Asking for sympathy / blowing off steam:

His MDs can't argue for PEX under the PANDAS dx, for even when Cam-K II was seriously high at ~184, the Cunningham strep-specific Aabs were BELOW normal threshold, and his ASOs have always been 0.  So Kiddo has either never had strep or he doesn't react.   

And silly me -- I  missed the 2nd "easiest" time to justify PEX a year ago when he had lost 15% of body weight due to gastroparesis/MCAS (after the last major mold exposure we didn't know about).  But at that point I wasn't thinking about PEX -- his anxiety was sky-high, he couldn't think, was getting scolded by his Pedi for not taking weight gain as a serious enough goal (he was trying!), he was given antipsychotics by a neurologist, and was threatened with a "behavioral eating disorders program".  I wasn't forcing him too eat, so he never wound up in the ER.  Instead his allergist gave him a tentative MCAS dx, nobody was talking autoimmunity as the mechanism, and so I jumped at the mast-cell stabilizer compounded drug -- instead of first investigating why he had mast cell activation, and making sure he threw up and had an ER visit to document the severity 🙄.).     

Or maybe he needs to stop taking the non-FDA-approved med for gastroparesis, and lose 10% of his body weight again -- shouldn't take too long 🙃(I'm kidding, but definitely frustrated by the catch-22. )