MCAS is not well understood and is probably not adequately diagnosed, since many of the symptoms are quite vague and could be attributable to many other things. I think the relationship between MCAS and mold toxicity is fascinating, and well worth further investigation. I wrote about the severity of mold toxicity here are while back, so for anyone suffering from MCAS, looking into mold exposure would be a good idea. I have also had a handful of patients with Lyme disease who also had MCAS. I have never used Low Dose Naltrexone in my patients who have presented with MCAS but given it is immune modulating, anti-inflammatory and is frequently used to balance auto-immune processes, it would seem to be worth a therapeutic trial.