Possible. Many people have flare-ups when they get infection UTI, upper respiratory while others have flare-ups when they are immune suppressed. I fall in the later category as I can get as sick as hell and my MS is fine but stress and lack of sleep will put me down every time.

Thank you for clarifying this! May I pose the question from a different view? I was diagnosed with tenosynovitis 2 weeks ago and am struggling with a flare up for a week now, no infections. It occurred to me last night, could the painful tenosynovitis now be what triggered my MS flare up?

Possible but likely not as myelin is the target of the immune system in MS and those other conditions likely have a different target of the immune system.