VANCOUVER (FRONTLINE MEDICAL NEWS) The risk of dimethyl fumarate lymphopenia – and perhaps progressive multifocal leukoencephalopathy – is greatest in patients 60 years or older and those with baseline absolute lymphocyte counts below 2 x 109/L, according to a review of 206 patients with relapsing-remitting or progressive multiple sclerosis from the University of Rochester (N.Y.).

A total of 87 patients (42%), all of whom were on dimethyl fumarate (DMF; Tecfidera) for at least 3 months, developed lymphopenia with an absolute lymphocyte count (ALC) below 0.91 x 109/L. That’s not a surprise; lymphopenia is a well-known side effect of the drug, and the rates in Rochester were similar to what was reported in clinical trials. The greatest concern with DMF lymphopenia is subsequent progressive multifocal leukoencephalopathy (PML); a handful of cases have been reported in lymphopenic patients, none in the University of Rochester review .

What was surprising was that in the 34 patients aged 60 years or older, 24 (71%) developed lymphopenia, versus 62 (36%) of the 172 under 60 years old (P = .0005). Meanwhile, of 93 patients with baseline ALCs below 2 x 109/L, 49 (53%) became lymphopenic, versus 34 of 104 patients (33%) who started DMF with higher lymphocyte counts (P = .0006). A total of nine patients in the study did not have a baseline ALC available.

“If I had a patient who was 70 years old with a low baseline lymphocyte count, [these findings] would weigh into my decisions about choosing” this medication. “Age and baseline ALC may guide future selection of patients for DMF therapy,” neurologist and investigator Dr. Jessica Robb said at the annual meeting of the American Academy of Neurology.

Also, because higher grade lymphopenia didn’t resolve in most cases until the drug was stopped, “if I had a patient who developed more severe grade 3 or 4 lymphopenia, I would probably have a lower threshold for” discontinuation. “I would probably think about changing medication more quickly rather than leaving them on [DMF] and hoping that their lymphopenia resolves,” Dr. Robb said.

The Rochester findings are in line with a 2015 report from Washington University, St. Louis, that also indicated a higher risk of moderate to severe lymphopenia in older patients and those with lower baseline ALCs, as well as recent natalizumab (Tysabri) users. Grade 2 or worse lymphopenia “is unlikely to resolve while on the drug,” the St. Louis investigators concluded ( Mult Scler J Exp Transl Clin. 2015 Jan-Dec;1:2055217315596994 ).

Taken together, the two studies are important because there’s otherwise not much else in the medical literature identifying DMF lymphopenia risk factors. Lymphopenia and PML are also concerns with other multiple sclerosis (MS) agents.

“The increased prevalence of lymphopenia in older patients and in patients with a lower baseline ALC suggests a failure of lymphopoiesis triggered by DMF therapy. Indeed, lymphopoiesis declines with age due to thymic involution and decreased production of naive lymphocytes. … Whether these consequences of normal aging could be amplified by DMF is an avenue for future study,” the St. Louis team said.

“The significance of increased risk for lymphopenia in patients recently exposed to natalizumab is not immediately obvious. … Natalizumab is known to expand circulating leukocytes, including progenitor cells. If in turn, DMF causes lymphocyte apoptosis or arrest of differentiation, then patients sequentially exposed to natalizumab and DMF might have a larger number of circulating lymphocytes vulnerable to DMF effects than other patients,” they said.

Food and Drug Administration labeling for DMF recommends lymphocyte counts at baseline, 6 months, and every 6-12 months thereafter. However, European regulators recently recommended lymphocyte counts at baseline and every 3 months to catch problems early, as well as baseline MRIs as references for possible PML.

Standard, 240-mg twice-daily dosing was used at the University of Rochester, and the mean age in the study was 49 years. The majority of patients were women, and the mean duration of MS was 11 years. Almost three-quarters of the patients were new to immunosuppression, and none of the patients developed serious infections.

The University of Rochester team noted a higher rate of grade 1 lymphopenia than reported in clinical trials (18% vs. 10%). Twelve patients (6%) discontinued DMF because of lymphopenia.

Dr. Robb and the other investigators had no relevant disclosures.