I’m so sorry this is happening to you.

I have small fiber neuropathy as well, believed to be triggered by a viral infection because I had a horrible cold (underwhelming, I know, but I was really sick) two weeks before onset of symptoms. And that started a cascade of other issues and diagnoses, including an autoimmune arthritis.

Yes, small fiber neuropathy can affect heart rate. The small fiber nerves influence sensation, temperate, and pressure in sensory neuropathy. But small fiber nerves also run your autonomic processes: heart rate, digestion, breathing, etc. I have both small fiber sensory and autonomic neuropathy. So I don’t think it’s a matter of believing whether or not it can; it’s one iteration of small fiber neuropathy.

I don’t have links to research to back this up, but it’s my understanding viral infections are a known trigger for several neurological conditions, including small fiber neuropathy.

Just like with other autoimmune conditions, something acts as a trigger (we don’t always know what) that flips a switch in the immune system, whether it’s an environmental factor, chronic stress, covid, etc. It’s one reason for those of us who’ve long had chronic pain/illness/fatigue, that long covid exists and has similar consequences and treatments doesn’t feel surprising, at least it wasn’t for me and seemingly with others on my care team.

Are you seeing a neurologist in addition to the person you’re seeing for MCAS?