The frequency of occurrence of atypical lymphocytes in peripheral blood smears of natalizumab-treated patients with multiple sclerosis.

ABSTRACT

INTRODUCTION: Aside from the extensive published data on immunophenotypic lymphocyte subsets in natalizumab-treated patients with multiple sclerosis (MS), an impact of natalizumab on lymphocyte morphology has rarely been studied. As patients treated with immunomodulating or immunosuppressive drugs are at risk for infectious disorders such as viral infections, knowledge of drug-derived changes in lymphocyte morphology may be beneficial in the diagnostic work-up in such clinical situations. This study aimed to determine the frequency of occurrence of atypical lymphocytes and defined subtypes of variant lymphocytes in natalizumab-treated patients with MS. METHODS: We compared eight defined morphological lymphocyte subtypes in peripheral blood smears between 14 natalizumab-treated, 13 interferon-treated and 10 untreated subjects with relapse-remitting MS. RESULTS: Atypical lymphocytes were significantly enhanced in natalizumab-treated patients compared to the interferon and control group (P<.0001). Binucleated lymphocytes were restricted to the natalizumab group (P=.0058, P=.018), and plasmacytoid lymphocytes were more frequently found in the natalizumab group (P<.0001). CONCLUSION: Our data indicate that natalizumab enhances the fraction of atypical lymphocytes, and thereby especially the binucleated and plasmacytoid lymphocytes. Knowledge of these natalizumab-associated changes in lymphocyte morphology may be relevant in clinical routine, to avoid unnecessary diagnostic procedures or even a discontinuation of natalizumab treatment.