How do you differentiate erythrodermic mycosis fungoides and Sezary syndrome - is it primarily based on the burden of blood involvement of malignant cells?

You are correct: Sezary and erythrodermic MF are not the same things, and Sezary is erythroderma (defined as 80% BSA or more) right from the start. But our current definition of Sezary also requires Stage B2 blood involvement, and specifically that the sum of CD4+ CD7- and CD4+CD26 - cells is > 1000...

Rather than the 1K marker which is often not reported on flow cytometry reports, there are 'proxy' percentages.

>30% of the LYMPHOCYTES (not of all the WBC) CD4+CD26- cells

OR

>40% of the LYMPHOCYTES (not all the WBC) CD4%CD7- cells

OR

CD4:CD8>10 with phenotypically abnormal cells (loss of other ea...