At what degree of lymphopenia do you switch/discontinue dimethyl fumarate in patients with multiple sclerosis?

I do not check the JC index status for my patients on fumarates. While I do not have recent data, to my knowledge, there are only a handful of PML cases attributed to fumarates used in MS. Even when including fumarates used in treating psoriasis, the PML numbers are small. Since the prognostic value...

Personally, I watch for absolute lymphocyte counts of 500-800/mm3 or less that are persistent for more than six months. I pay more attention to that point and consider rechecking labs sooner (quarterly instead of every six months) when a patient drops below 1000/mm3.

I also like to make note of a pat...