Yes, Tecfidera can cause low lymphocytes. In controlled trials, lymphocyte counts decreased by an average of 30% during the first year of treatment with Tecfidera but remained stable thereafter. When Tecfidera was discontinued, lymphocyte counts increased, although they did not return to pre-treatment levels.

Lymphocytes are a type of white blood cell and a normal lymphocyte count for adults is usually between 1,000 and 4,800 lymphocytes per microliter of blood (x 10⁹/L). 6% of Tecfidera patients in clinical trials experienced lymphocyte counts of less than 0.5 x 10⁹/L compared to less than 1% of people administered a placebo ( a medicine that contains no active ingredient).

Tecfidera (dimethyl fumarate) is an oral medication that may be used to treat relapsing forms of multiple sclerosis (MS) in adults, which includes clinically isolated syndrome, relapsing-remitting disease, and active secondary progressive disease.

What does a low lymphocyte count with Tecfidera mean?

Low lymphocyte counts are a sign of a suppressed immune system, which can increase your risk of infection, lower your response to vaccinations, and put you at risk of other conditions.

Surprisingly, in clinical trials, the incidence of infections was similar when Tecfidera was compared with placebo (mild-to-moderate infections: 60% with Tecfidera and 58% with placebo; serious infections: 2% with Tecfidera and 2% with placebo). However, since Tecfidera was approved in 2013, postmarketing surveillance and reports have revealed it is associated with several secondary immune-related complications. These include:

• Pronounced lymphocytopenia (decreased lymphocytes) of below 500/µl have been reported in 4–6% of patients that may persist for several weeks or months (mostly CD8 counts and to a lesser extent, CD4 counts)
• Progressive multifocal leukoencephalopathy (PML) an opportunistic viral infection of the brain caused by the JC virus (JCV) that usually only occurs in patients who are immunocompromised and is often fatal or leaves the person severely disabled. Symptoms include progressive weakness on one side of the body or clumsiness of limbs, disturbance of vision, and changes in thinking, memory, and orientation leading to confusion and personality changes.
• Severe herpes zoster including disseminated herpes zoster, herpes zoster ophthalmicus, herpes zoster meningoencephalitis, and herpes zoster meningomyelitis
• Serious viral infections, such as those caused by herpes simplex virus, West Nile virus, or cytomegalovirus; serious fungal infections (Candida and Aspergillus), and serious bacterial infections, such as those caused by Nocardia, Listeria monocytogenes, or Mycobacterium tuberculosis).
• Eosinophilic gastroenteritis a rare gastrointestinal disease that may be autoimmune in origin. Investigate any cases of protracted and severe GI symptoms

How can you reduce the risk of lymphocytopenia with Tecfidera?

Before starting treatment with Tecfidera, your doctor should obtain a CBC (complete blood count) and then repeat this in 6 months and then every 6 to 12 months thereafter. If your lymphocyte count falls below 0.5 x 10⁹/L and persists at that level for more than six months, then your doctor may consider temporarily discontinuing Tecfidera until it increases again. Your doctor may also consider withholding Tecfidera if you develop a serious infection.

The decision to restart Tecfidera should be based on your clinical circumstances.