The National Multiple Sclerosis Society states that Tecfidera’s, formerly known as BG-12, mechanism of action is not known, but it is theorized that Tecfidera inhibiting the immune system helps with MS treatment.
According to the National Institute of Neurological Disorders and Stroke, PML is a rare disease of the white matter of the brain caused by the polyomavirus JC and associated with individuals with compromised immune systems. The patient who developed PML had been on Tecfidera for over four years and had suffered from lymphopenia, which is a risk factor for developing PML, according to Reuters.
The National Institutes of Health report the symptoms of PML include:
MultipleSclerosis.net reports that the symptoms of PML can mimic the symptoms of multiple sclerosis, making it difficult to diagnosis in MS patients. The National Institute of Neurological Disorders and Stroke reports that mortality rate is between 30 and 50% and that those who survive may be left with permanent neurological disabilities.
The National Multiple Sclerosis Society reports that a drug similar to Tecfidera, called Fumaderm, active ingredients dimethyl fumarate and fumaric acid ester, has been used in Europe for decades in the treatment of psoriasis.
Fumaderm and Psorinovo, dimethyl fumarate with copper, have been associated with PML in psoriasis patients in Europe, according to MultipleSclerosis.net. The New England Journal of Medicine has case reports of patients on these drugs, fumaric acid and Psorinovo, developing progressive multifocal leukoencephalopathy after having been on these medications for several years.
FiercePharma reports the maker of Tecfidera, Biogen Idec, removed a previous MS drug, Tysabri, from the market for a period of time after patients taking it developed PML.