Objective: N/A

Background: “Rabbit” syndrome (RS), also known as oral vertical dyskinesia is a rare movement disorder characterized by involuntary, rhythmic vertical movements, primarily affecting the perioral region without tongue involvement. These movements typically occur at rest with an average frequency of 5Hz. Orofacial tardive dyskinesia (TD) is frequently misidentified as RS, both conditions associated with antipsychotic use. TD manifests with irregular, stereotyped movements of the mouth, commonly involving the tongue, and is worsened by anticholinergic medications unlike RS. Reported risk factors for RS are similar to other drug induced movement disorders, with some data suggesting ethnic and genetic predispositions. The underlying mechanism driving RS is poorly understood with studies suggesting similarities to both drug-induced parkinsonism (DIP) and TD. Here, we present a unique case of RS with concomitant a re-emergent tongue tremor that improved with levodopa therapy.

Method: N/A

Results: A 58-year-old Hispanic female with a history of restless leg syndrome (RLS) on ropinirole and depression on aripiprazole, lamotrigine, and paroxetine initially presented for worsening RLS. On exam, she described symptoms of RLS augmentation and exhibited bilateral postural kinetic tremor with left sided rest tremor and left greater than right rigidity and bradykinesia. A DaTscan, obtained to differentiate between degenerative parkinsonism and DIP showed normal radiotracer uptake. Ropinirole was replaced with pregabalin with marked improvement in RLS symptoms. Three months following medication adjustment, the patient returned for involuntary mouth movements. The subsequent exam showed rhythmic vertical lip movement at rest and similar frequency re-emergent tongue tremor on tongue protrusion with mild limb bradykinesia. Movements significantly improved after starting carbidopa/levodopa.

Conclusion: The movement pattern of the lips in this patient is consistent with the known phenomenology of “rabbit” syndrome.  However, the concomitant re-emergent tongue is atypical with this syndrome and it is more commonly a feature of Parkinson’s disease tremor. Given the possible shared mechanism between RS and DIP, this case may represent a co-occurring phenomenon or support RS being part the DIP spectrum.

References: Catena Dell’osso M, Fagiolini A, Ducci F, Masalehdan A, Ciapparelli A, Frank E. Newer antipsychotics and the rabbit syndrome. Clin Pract Epidemiol Ment Health. 2007;3:6. Published 2007 Jun 11. doi:10.1186/1745-0179-3-6

Rissardo JP, Kherajani K, Vora NM, et al. A Systematic Review of Oral Vertical Dyskinesia (“Rabbit” Syndrome). Medicina (Kaunas). 2024;60(8):1347. Published 2024 Aug 19. doi:10.3390/medicina60081347

Singh R, Chakrabarti SS, Kaur U. Atypical extrapyramidal manifestation of a typical antipsychotic with serotonergic antidepressant. Daru. 2024;32(1):439-441. doi:10.1007/s40199-023-00489-5

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MDS Abstracts - https://www.mdsabstracts.org/abstract/a-case-of-rabbit-syndrome-with-concomitant-tongue-tremor/