Reversible granulocytopenia in association with riluzole therapy

To report a case of severe neutropenia developing in association with riluzole 200 mg/d.

A 63-year-old woman with amyotrophic lateral sclerosis (ALS) presented with nausea, anorexia, and fever two weeks following inadvertent dose escalation of riluzole from 100 to 200 mg/d. Granulocytopenia was diagnosed and evaluation for a possible causative infectious process was negative; riluzole was considered a possible offender. Blood counts returned to normal with discontinuation of riluzole and administration of filgramstim.

Riluzole is a glutamate release inhibitor used in the treatment of ALS, a devastating, progressive neurodegenerative disorder affecting motor neurons. A variety of adverse effects have been described with riluzole therapy, most commonly dizziness and gastrointestinal disorders. In this patient, multiple investigations failed to reveal an infectious cause or other drug-induced cause for the granulocytopenia.

Granulocytopenia has been reported as an adverse effect of riluzole but is not a complication well known to clinicians, and there are no detailed reports published in the literature. In this patient, several lines of evidence raise the possibility of a causal relationship between riluzole and granulocytopenia.