Glossopharyngeal Dystonia Secondary to a Lurasidone-Fluoxetine CYP-3A4 Interaction

Acute dystonic reactions are becoming much less prevalent in clinical practice due to the use of newer antipsychotics. Drug-drug interactions, patient characteristics, and environmental and genetic factors all contribute to the rate of occurrence of acute dystonia with second generation agents. In this case, we report a glossopharyngeal dystonia secondary to a lurasidone-fluoxetine CYP-3A4 interaction to highlight the importance of maintaining an index of suspicion for laryngeal dystonia, a potentially fatal dystonia. 1. Introduction Both first-generation antipsychotics (FGA) and second-generation antipsychotics (SGA) have equal efficacy in treating positive symptoms of schizophrenia; however, SGAs are now considered to be first-line agents, mainly because they have less propensity for side effects, including extrapyramidal symptoms (EPS), tardive dyskinesia (TD), weight gain, and metabolic side effects [1, 2]. The rates for EPS for haloperidol, clozapine, and chlorpromazine are estimated at 20%, 12%, and 25%, respectively [2, 3]. However despite choosing a SGA, acute EPS may still occur, with the rates ranging from 1 to 10% depending on the agent [4]. FGAs can cause EPS at a higher rate than SGA [5]. The prototypical high potency and arguable “gold standard” FGA is haloperidol, which is noted to have a prevalence rate of 35–52% for akathisia and 55% for parkinsonism [4]. A 2006 Cochrane meta-analysis of 21 studies including about 1500 individuals with schizophrenia reported a number needed to harm (NNH) of 5 with regard to acute dystonia. An NNH of 5 indicates that of 5 people treated with haloperidol, 1 individual will have an acute dystonic event [3]. Typically, acute dystonia occurs within hours of administration and consists of acute contracture of a muscle group resulting in a very uncomfortable position and significant psychological distress. Although all muscle groups can be involved, the most common are the eyes (oculogyric crisis), the neck (torticollis), tongue (glossopharyngeal) the back, the arms, and the large muscle groups of the legs. Risk factors for acute dystonia include male sex, age less than 35, high potency typical antipsychotics, intramuscular route of delivery, previous dystonic reactions, and recent cocaine use [4]. Over the past 6 years, multiple antipsychotics have been approved by the Food and Drug Administration (FDA) for the treatment of schizophrenia, including paliperidone (2006), iloperidone (2009), asenapine (2009), and lurasidone (2010). Although the incidence of acute dystonia is established to be lower than