A Severe Parkinsonian Presentation Mimicking Catatonia: Lessons from a Case Report with Features of Rabbit Syndrome

Introduction: Rabbit Syndrome (RS) is a rare antipsychotic-induced movement disorder classically characterized by a fine vertical perioral tremor. Although traditionally considered a distinct extrapyramidal syndrome, it may coexist with drug-induced parkinsonism (DIP), and both conditions may share clinical and pathophysiological features. We describe an unusual case of RS following abrupt discontinuation of chronic psychotropic and anticholinergic treatment emerging within a severe parkinsonian syndrome that closely mimicked catatonia. Case presentation: A 61-year-old man with schizophrenia, moderate intellectual disability, previous antipsychotic-induced parkinsonian symptoms, and chronic biperiden treatment developed sudden mutism, rigidity, and complete lack of interaction after abdominal sepsis and interruption of psychotropic and anticholinergic treatment. Initial neurological assessment, blood tests, and brain CT were unremarkable. DSM-5-TR criteria for catatonia were met, and the Bush–Francis Catatonia Rating Scale score was 14/69. First-line catatonia treatment produced no improvement. Neurological reassessment identified a characteristic 4–5 Hz vertical jaw tremor together with marked axial and appendicular rigidity. Intravenous anticholinergic treatment led to marked clinical improvement within 48–72 hours. The presentation was interpreted as an atypical form of RS, with re-emergent DIP following abrupt withdrawal of chronic biperiden treatment. Conclusions: Severe parkinsonian presentations may closely mimic catatonia. In this case, the perioral movements suggested RS, while concomitant DIP may have contributed to the marked rigidity and hypokinesia. Careful characterization of movement phenomenology and recent medication changes may be crucial for distinguishing catatonic from extrapyramidal presentations. This case may also be relevant to selected cases of acute functional regression in individuals with intellectual disability.