Background Dimethyl fumarate (DMF) is prescribed for the treatment of adult patients with relapsing remitting multiple sclerosis (RRMS). Although mild to moderate adverse reactions such as flushing and gastrointestinal events are common, haematologic abnormalities may also occur. Haematologic abnormalities are usually of limited clinical relevance. Particularly, transient eosinophilia has been reported within 2 months of DMF treatment, which could lead to significant damage to tissues, skin, airway, gastrointestinal tract, and the cardiac and nervous system.

Purpose This research aimed to clarify the relationship between DMF treatment and the development of severe eosinophilia in RMSS patients.

Material and methods A 25-year-old male RRMS patient, diagnosed in 2007, was treated with interferon beta-1b, natalizumab and glatiramer acetate. In October 2015, the patient switched to DMF treatment due to lesions on MRI. DMF was administered 120 mg once a day for 7 days, followed by 120 mg twice a day for 7 days, 120 mg in the morning and 240 mg in the afternoon for 14 days, and finally the recommended dose of 240 mg twice a day. The patient suffered flushing and gastrointestinal events, commonly associated with DMF treatment, and omeprazole 20 mg twice a day was administered. After 1 month under the recommended dose, laboratory tests showed severe leukocytosis (19420/μL) and eosinophilia (5950/μL). DMF and omeprazole were removed, prednisone 1 mg/kg was administered for 13 days in decreasing doses and laboratory tests were repeated. The relationship between DMF treatment and the appearance of eosinophilia was evaluated using a modified Karch–Lasagna algorithm.

Results The second laboratory tests showed normal levels of eosinophils and the patient did not suffer any tissue damage. According to the modified Karch–Lasagna algorithm, the present case corresponds to a possible adverse reaction (score 4). This reaction was reported to the Regional Pharmacovigilance Centre.

Conclusion In this case, severe eosinophilia could have been caused by DMF, omeprazole or both drugs as omeprazole may also be associated with eosinophilia. Patients treated with DMF and omeprazole could require pharmacovigilance in order to prevent the development of severe eosinophilia.

References and/or acknowledgements Xu Z, et al. Dimethyl fumarate for multiple sclerosis. Cochrane Database Syst Rev2015.

Pérez-Arellano JL, et al. Manejo práctico de una eosinofilia. An Med Interna (Madrid) 2004;21:244–52.

No conflict of interest