Tardive Dyskinesia
The most likely cause of constant lip-smacking in this patient who recently discontinued long-term risperidone is tardive dyskinesia (Answer A). This presentation is classic for tardive dyskinesia, which characteristically manifests as involuntary orofacial movements including lip-smacking, and is associated with long-term antipsychotic use 1.
Clinical Reasoning
The key diagnostic features pointing to tardive dyskinesia in this case are:
- Long-term risperidone exposure: Tardive dyskinesia is typically associated with chronic neuroleptic use 1
- Orofacial involvement: TD characteristically presents as "athetoid or choreic movements in the orofacial region," with lip-smacking being a hallmark symptom 1
- Timing after discontinuation: The presentation occurred after cessation of the antipsychotic, which is consistent with either tardive dyskinesia or withdrawal dyskinesia 1
Distinguishing from Other Options
Why not acute dystonia (B)? Acute dystonia involves "sudden spastic contraction of distinct muscle groups" and typically occurs within hours to days after starting or increasing antipsychotic doses, not after discontinuation 1. It presents with oculogyric crisis, torticollis, or laryngospasm—not repetitive lip-smacking 2.
Why not torticollis (C)? Torticollis is a specific type of dystonic reaction affecting neck muscles, not a diagnosis that explains orofacial movements like lip-smacking 1.
Why not neuroleptic malignant syndrome (D)? NMS presents with the tetrad of mental status changes, fever, rigidity, and autonomic dysfunction 2. This patient has isolated movement symptoms without systemic features.
Important Clinical Distinction: Tardive vs. Withdrawal Dyskinesia
A critical nuance here is that this could represent either:
- Tardive dyskinesia: Persistent involuntary movements that may continue indefinitely even after drug discontinuation 1
- Withdrawal dyskinesia: Occurs with cessation of neuroleptics but "almost always resolves over time" 1
The guideline evidence indicates that "as many as 50% of youth receiving neuroleptics may experience some form of tardive or withdrawal dyskinesia," and "withdrawal dyskinesias almost always resolve over time, whereas TD may persist even if the antipsychotic agent is discontinued" 1.
Clinical Management Implications
The distinction matters for prognosis but not for immediate diagnosis. At presentation, both are classified under tardive dyskinesia, with time determining whether symptoms resolve (suggesting withdrawal dyskinesia) or persist (confirming true TD) 1.
Risperidone-specific risk: While risperidone is an atypical antipsychotic theoretically associated with lower extrapyramidal side effects than typical antipsychotics, it "still has some antidopaminergic activity and can produce extrapyramidal symptoms" 1. The FDA label confirms cases of tardive dyskinesia have been reported with risperidone 3.
Common Pitfall
Do not assume atypical antipsychotics like risperidone are immune to causing tardive dyskinesia. The evidence clearly shows that "there are also case reports of neuroleptic malignant syndrome and tardive dyskinesia in adults and teenagers taking risperidone" 1.