Introduction: Pisa syndrome is a drug-induced dystonia characterized by lateral truncal flexion. “A metronome-like pattern,” a rare variant characterized by alternating directions of deviation, may offer insights into the pathophysiology of extrapyramidal symptoms. This case report describes a rare case of Pisa syndrome induced by aripiprazole, in which the direction of truncal deviation changed following biperiden administration.Case: We describe a 41-year-old female with rapid-cycling bipolar disorder treated with aripiprazole and clozapine who presented with marked rightward truncal flexion. Given her acute manic state, the anticholinergic agent biperiden was added to manage the dystonia without reducing antipsychotic dosage. Surprisingly, this intervention coincided with a shift of the deviation to the left-a phenomenon consistent with a metronome-like pattern. The condition resolved completely following a reduction in aripiprazole dose.
Conclusion: This case may support the view that Pisa syndrome is a dynamic state sensitive to the equilibrium between dopaminergic and cholinergic systems. We hypothesize that the anticholinergic effect of biperiden, combined with aripiprazole’s partial agonist activity, precipitated the directional switch. Clinicians should be aware of this “direction-switching” phenomenon when managing drug-induced movement disorders in complex polypharmacy regimens.
Keywords: Aripiprazole, biperiden, case report, drug-induced dystonia,