The following article is part of conference coverage from the 2019 Annual Meeting of the Consortium of Multiple Sclerosis Centers , in Seattle, Washington. MPR‘s staff will be reporting breaking news associated with research conducted by leading experts in neurology. Check back for the latest news from CMSC 2019.

SEATTLE – Individuals with multiple sclerosis undergoing dimethyl fumarate therapy may be vulnerable to herpes simplex encephalitis and grade 3 lymphocytopenia. This research was recently presented at the 33rd Annual Meeting of the Consortium of Multiple Sclerosis Centers, held May 28 to June 1, 2019, in Seattle, Washington.

In this case review, the study researchers followed an individual treated with dimethyl fumarate for 39 months. Data were systematically collected and collated. The individual developed herpes simplex encephalitis and grade 3 lymphopenia, at which point treatment was switched to teriflunomide.

The individual’s lymphocyte counts persisted for 25 months in the high grade 2 range (above 700). At 32 months, the cumulative lymphocyte count was significantly abnormal at 506, by which point the individual had remained clinically stable for the duration of the study. At the 36-month mark, clinical stability continued with an improved lymphocyte count of 609. However, the lymphocyte count decreased to 482 at 39 months, leading to the clinical decision to switch from dimethyl fumarate to teriflunomide. The individual was clinically stable throughout this time and through the 42-month follow-up period. Two days after follow-up, the individual showed symptoms including seizures, non-normal mental state, and a brain magnetic resonance image that suggested herpes simplex encephalitis. This diagnosis was confirmed through a positive test for herpes simplex polymerase chain reaction in the individual’s cerebral spinal fluid.

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The study researchers concluded that “[grade] 3 lymphocytopenia may evolve relatively late in the course of dimethyl fumarate therapy, and patients, even in the high grade 2 range, may be most vulnerable. This is the second case of dimethyl fumarate–associated herpes simplex encephalitis reported at the time of this submission.”

Author DA Barone reports financial associations with Sanofi Genzyme and Biogen.

Visit MPR‘s conference section for continuous coverage from CMSC 2019.


Barone DA, Barone KA. Herpes simplex encephalitis associated with lymphopenia during transitional multiple sclerosis immunotherapy. Presented at: 33rd Annual Meeting of the Consortium of Multiple Sclerosis Centers; May 28-June 1, 2019; Seattle, WA. Abstract DXT76.

This article originally appeared on Neurology Advisor