Interferon-β therapy and risk of thrombocytopenia in multiple sclerosis patients.

Thrombocytopenia is a well-described adverse event of several disease-modifying therapies (DMT) in multiple sclerosis (MS). On the other hand, an increased prevalence of MS has been reported in patients with immune thrombocytopenia. In this retrospective, cross-sectional, case-control study we evaluated in a heterogeneous MS cohort: (1) the prevalence of thrombocytopenia in comparison with sex- and age-matched controls; (2) the relationship between thrombocytopenia and patients' demographic, clinical characteristics; (3) the risk for thrombocytopenia in relation to DMT. 187 consecutive MS patients [51 males, mean age (±SD) 44.5 ± 10.7 years] and 200 controls (56 males, mean age 45.5 ± 12 years) were included. Thrombocytopenia was defined as platelet count lower than normal laboratory values (130-400 × 10(9)/L). The prevalence of thrombocytopenia was significantly higher in MS patients than in controls (7 vs. 2.5 %, p = 0.04). Thrombocytopenia was present only in relapsing-remitting MS cases, and significantly associated with lower EDSS (p = 0.002) and with a trend for shorter disease duration (p = 0.06). It was more frequent in patients on high-dose interferon-β therapy compared with those on low-dose interferon-β therapy, other therapies or untreated patients (p = 0.02). High-dose interferon-β therapy was associated with more than eightfold increase in the risk for thrombocytopenia (odds ratio 8.60, 95 % confidence interval: 1.01-74.48 adjusted for EDSS, disease duration and type of disease). The prevalence of thrombocytopenia was increased in MS patients treated with DMT. High-dose interferon-β therapy is the variable most strongly associated with thrombocytopenia.