Rabbit syndrome is an involuntary movement disorder affecting the mouth and lips, often appearing as a side effect of certain medications. Also known as rabbit-like movements or perioral tremor, it involves rhythmic motions that resemble a rabbit’s chewing. It represents a specific type of drug-induced movement.
Characteristics and Symptoms
Rabbit syndrome involves distinctive, involuntary movements primarily of the mouth and lips. These movements are fine, rapid, and rhythmic motions of the lips, occurring along a vertical plane at approximately 5 Hz, or 5 cycles per second.
The movements involve the entire labial musculature and masticatory apparatus. A distinguishing feature is that these movements generally do not involve the tongue, setting it apart from other movement disorders. The movements are usually observed when the individual is at rest.
Individuals may be able to voluntarily suppress these movements for a short duration. The lip movements can be bilateral or appear unilaterally.
Causes of Rabbit Syndrome
Rabbit syndrome is primarily linked to the long-term use of certain medications, particularly antipsychotic drugs. Typical antipsychotics, such as haloperidol, fluphenazine, and pimozide, are more commonly linked to this syndrome. The condition can also occur, though less commonly, with atypical antipsychotics like clozapine, olanzapine, aripiprazole, and low doses of risperidone.
The underlying neurological mechanism involves the basal ganglia in the brain, specifically the substantia nigra pars reticulata. This area plays a role in controlling movement, and disruptions here can lead to involuntary motions. Rabbit syndrome can develop after months or even years of continuous antipsychotic treatment.
Rabbit syndrome is distinct from tardive dyskinesia, another drug-induced movement disorder, primarily because it does not involve tongue movements. While the exact pathophysiology is not fully understood, it is generally considered an extrapyramidal side effect of these medications. The reported prevalence in patients treated with typical antipsychotics ranges from 2.3% to 4.4%.
Diagnosis and Management
Diagnosing rabbit syndrome primarily relies on clinical observation of the characteristic involuntary movements of the mouth and lips. A review of the patient’s medication history is also an important step, particularly noting any long-term use of antipsychotic drugs. The absence of tongue involvement helps differentiate it from other conditions like oral tardive dyskinesia.
Management strategies for rabbit syndrome involve adjusting or discontinuing the causative medication, if clinically appropriate for the patient’s overall treatment plan. Switching to alternative medications, such as atypical antipsychotics with different pharmacological profiles, may also be considered. Some atypical antipsychotics possess high anticholinergic properties, which can be beneficial in symptom reduction.
Specific anticholinergic drugs are a treatment option for managing the symptoms of rabbit syndrome. These medications aim to reduce the involuntary movements. The goal of management is to control symptoms and improve the individual’s quality of life, recognizing that complete elimination may not always be feasible without full withdrawal of the antipsychotic treatment.