Fluoxetine-Induced “Rabbit Syndrome” in a Child With Juvenile Obsessive-Compulsive Disorder

Abstract

An 11-year-old Iraqi male youngster has been assessed in our outpatient clinic for ablutomania whereby a DSM-5 (Diagnostic and Statistical Manual of Mental Disorders, fifth Edition) diagnosis of obsessive-compulsive disorder (OCD) with fair insight was entertained. He had a heavy genetic load (a mother with OCD on fluoxetine, an elder sister with trichotillomania also on fluoxetine) but no tics. He was trialled before on sertraline 150 mg/d for 12 weeks but to no avail in a private psychiatric clinic. He was also enrolled in Cognitive-Behavioural Therapy sessions, albeit with erratic attendance but found unhelpful. At our facility, he was prescribed fluoxetine (for possible pharmacogenetics) at 10 mg/d and uptitrated (increments of 5 mg/wk) to 30 mg/d over month duration. Yale-Brown Obsessive-Compulsive Scale (Y-BOCS) severity was readministered and scored 26 (severe), and patient was still undermarked distress. We opted to go for fluoxetine 40 mg/d over another 2 weeks with tangible improvement both on self-reports parents' reports and a drop in Y-BOCS down to 15 (mild). However, at this dose, both patient and parents noticed fast perioral rest tremors. No tongue involvement or rigidity was demonstrated. These were socially embarrassing. No anxiety concomitants could be detected on Mental Status Examination. Neurological consult was summoned. electro-encephalo-graphy and electro-myo-graphy were performed. A diagnosis of "rabbit syndrome" was entertained. Fluoxetine dose was decreased down to 20 mg/d. After 10 days, tremors totally abated, but OCD symptoms re-emerged. Fluoxetine pushed back to 30 mg/d, and tremors reappeared. Fluoxetine was the culprit agent. Naranjo Adverse Drug Reaction Probability Scale scored 8 ("Probable"). Given the previous favorable response on fluoxetine 40 mg/d, dose was cautiously and slowly upped under cover of add-on procyclidine 2.5 mg/d. Dose was then welltolerated with no tremors altogether, and OCD symptoms remitted (Y-BOCS read 12). Sixteen weeks have elapsed at time of writing this report, and patient keeps faring well. Viva voce consent of parents was obtained beforehand to report this case anonymously."Rabbit syndrome" is uncommon extrapyramidal syndrome typically seen with chronic treatment (a year or more) with a conventional antipsychotic. It has also been reported with atypical antipsychotics as well. 1 This largely reflects dopaminergic blockade in the nigro-striatal