Aleukemic leukemia presenting with paranoid psychosis.

Mast cells not only synthesize and release serotonin, but also express and are activated through multiple serotonin receptors. Low blood serotonin level might define a specific subset of patients with systemic mastocytosis (SM) who are more likely to present with neurologic and gastrointestinal complaints. Mast cell leukemia (MCL) is a rare and aggressive type of systemic mastocytosis, and psychiatric manifestations in its course have not been well-characterized. We describe herein a unique patient with a KIT D816V mutation positive a leukemic leukemia variant of systemic mastocytosis with gastrointestinal involvement, presenting with a severe and sustained paranoid delusional illness. While diarrhea improved with the use of histamine H1 and H2 receptor antagonists, the psychosis did not, and the disease followed a dramatic course with a rapidly fatal outcome. As there is paucity of literature, diagnosis of MCL presenting with psychiatric symptoms remains a diagnostic challenge and warrants clinicians to be alert of this rare possibility.