Now again, the evidence for the antiserotonin-connection isn't particularly high and also very old (1992 & 1995 by one group, 2001 by another). For instance an article from 2008 summing this up, authored amongst others by "one of our experts" Daniel Clauw, said it's praps even less clear than the tender points, which they at that time were still defending a bit. They reviewed evidence for 15 sets of biomarkers and came to the conclusion: "Of the objective tests, those that hold the most promise as biomarkers are probably tests that directly assess elements of neural function, such as functional neuroimaging, ERPs, and DNIC."
"Antiserotonin antibody noted to be increased in three cross-sectional studies by two different groups.
Stringent controls necessary prior to determining utility. Longitudinal studies needed."
Not sure if that's interesting for
@miamisunset - it says "Autonomic reactivity: Lower heart rate variability noted in three cross-sectional studies by two different groups. May predispose to condition. Longitudinal studies needed"
That study is called "Biology and therapy of fibromyalgia. Evidence-based biomarkers for fibromyalgia syndrome" (2008).
The second highest autoantibodies ("71%") next to the ones for serotonin ("73%") are gangliosides: "Gangliosides may be an important aspect of FM autoimmunity. They’re believed to be involved in small-fiber neuropathy."
A more recent article (2019) quoting this and quoted by verywellhealth is: Neuroimmunology: What Role for Autoimmunity, Neuroinflammation, and Small Fiber Neuropathy in Fibromyalgia, Chronic Fatigue Syndrome, and Adverse Events after Human Papillomavirus Vaccination?
What confuses any clear conclusions for me is that antiserotonin antibodies might reduce the serotonin released by mast cells, or more generally serotonin can be high in mast cell disorders, of which I have MCAS.