Late-onset clozapine-induced agranulocytosis in a patient with comorbid multiple sclerosis.

The risk of clozapine-induced agranulocytosis is highest in the initial 6 months after onset of treatment. There have been very few reports of neutropenia and agranulocytosis after this period. We report a unique case of delayed clozapine-induced agranulocytosis in a patient with preexisting multiple sclerosis (MS) which was treated with granulocyte colony-stimulating factor. Both MS and clozapine-induced agranulocytosis have an underlying autoimmune immune mechanism. This case highlights the need for frequent blood count monitoring on clozapine even after the initial 6 months of starting treatment especially in patients with a past history of drop in white blood cell counts as well as with a comorbid autoimmune disorder.