Effect of dosage reduction on peripheral blood lymphocyte count in patients with multiple sclerosis receiving long-term fingolimod therapy.

Of the 19 cases of fingolimod-associated progressive multifocal leukoencephalopathy (PML) reported worldwide by the end of 2017, 4 cases were from Japan. This may indicate that fingolimod sensitivity is higher in the Japanese population than in the western population because the fingolimod dosage used for the prevention of multiple sclerosis (MS) is the same in both populations. Therefore, the laboratory data of nine patients with MS receiving fingolimod treatment for more than 2 years were retrospectively collected. Moreover, the effect of drug holiday was compared between five patients who underwent at least 3 months of dosage reduction via drug holiday after receiving fingolimod for more than 2 years and three patients who underwent drug holiday after receiving fingolimod for less than 2 years. The total, CD3(+), CD4(+), C19(+) lymphocyte counts, the CD4(+)/CD8(+) cell ratio, and the serum IgG concentrations were similar between Japanese patients with MS receiving fingolimod for more than 2 years and Western patients from the previous reports. Recovery of lymphocyte counts in the peripheral blood after fingolimod dosage reduction was worse in some MS patients who received long-term fingolimod treatment than in MS patients who received short-term fingolimod treatment. My findings indicate that the currently used fingolimod dosage may be too high for some Japanese MS patients receiving long-term fingolimod treatment.