Dear Editor,

Rasmussen’s encephalitis (RE) is a rare, progressive, inflammatory neurologic disorder affecting a single cerebral hemisphere and was first described by Rasmussen in 1958 [1]. Although RE predominantly affects children, approximately 10% of cases occur in adults, in whom the disease progresses more slowly and whose neurologic deficits are milder [2]. The core clinical features of this disease include refractory focal epilepsy, progressive hemiplegia, and cognitive decline, with only a few reports from Korea [3]. RE presenting primarily as a movement disorder is exceptionally uncommon, with only a few cases reported in the literature [4,5]. Herein, we describe a case of adult-onset RE presenting with parkinsonian features and cognitive decline without epilepsy, which, to our knowledge, is the first reported case in Korea.

A 56-year-old man presented with a 1-year history of left-sided slowness of movement and cognitive decline. He required a walking aid and exhibited memory impairment and personality changes. There was no anosmia, rapid eye movement sleep behavior disorder, or autonomic dysfunction.

Neurologic examination revealed left-sided bradykinesia, postural instability, and reduced left arm swing during gait, without tremor or rigidity. The Unified Parkinson’s Disease Rating Scale (UPDRS) Part III score was 9 (finger tap 1, rapid alternating movement of hands 1, leg agility 1, arising from chair 2, posture 1, gait 1, postural instability 1, bradykinesia 1). Increased cortical function testing demonstrated ideomotor apraxia and sensory neglect. Cognitive assessment revealed scores of 18/30 on the Korean Mini-Mental State Examination (K-MMSE) and 13/30 on the Korean Montreal Cognitive Assessment (K-MoCA). On the Seoul Neuropsychological Screening Battery (SNSB), attention was at the 17.59 percentile, whereas language, visuospatial function, memory, and executive function were all below the 0.01 percentile.

Blood and cerebrospinal fluid studies, including vasculitic, rheumatologic, autoimmune, and paraneoplastic panels, were unremarkable. Electroencephalography (EEG) revealed diffuse theta and delta slowing without epileptiform discharges, and video-nystagmography was normal.

Brain magnetic resonance imaging (MRI) revealed right hemispheric global cortical atrophy with fluid-attenuated inversion recovery hyperintensity in the subcortical white matter, insular cortex, putamen, periventricular white matter, and centrum semiovale (Figure 1). Brain magnetic resonance angiography revealed mild-to-moderate stenosis at the right common carotid artery bifurcation (Supplementary Figure 1). 18F-fluorodeoxyglucose positron emission tomography (PET) revealed hypometabolism in the right cerebral cortex, putamen, and thalamus (Supplementary Figure 2). 18F-fluoropropyl-carbomethoxy-3β-4-iodophenyltropane PET revealed reduced dopamine transporter uptake in the right dorsal striatum (Supplementary Figure 3).

Under the working diagnosis of RE, the patient received intravenous methylprednisolone (1 g/day for 5 days) followed by oral prednisolone, without clinical improvement. Levodopa/carbidopa (100/25 mg three times daily) was subsequently initiated, resulting in improved cognitive function and alleviated symptoms of parkinsonism. Oral prednisolone was discontinued, and azathioprine (50 mg twice daily) was added.

Three months later, the patient scored 25 on the K-MMSE and 20 on the K-MoCA. On the SNSB, attention remained unchanged, but significant improvements were observed in language, visuospatial function, memory, and executive function. Follow-up MRI showed no progression (Supplementary Figure 4), and EEG demonstrated delta slowing confined to the right hemisphere. The UPDRS Part III score improved to 1 (finger tap 1), and the patient regained independent ambulation. Memory impairment persisted, but he was able to engage in daily conversation.

The patient presented with parkinsonian features, cognitive decline, and cortical symptoms such as apraxia and neglect. Although corticobasal syndrome was initially suspected, MRI findings of unilateral hemispheric cortical atrophy with subcortical hyperintensity suggested an autoimmune etiology, particularly RE [4].

Notably, the main manifestation was parkinsonian features rather than seizures, which are typically the initial symptoms of RE. Parkinsonism is usually caused by dopaminergic neuronal loss in the substantia nigra; however, in this case, unilateral cortical and putaminal atrophy indicated secondary parkinsonism caused by dysfunction of the cortico-basal ganglia-thalamic circuit [5]. Clinical improvement was observed after combined immunosuppressive and dopaminergic therapy; however, the relative contribution of each treatment remains uncertain.

Seizures, the most common initial symptom of RE, were absent in this patient even after two years of disease onset. Although rare, cases in which hemiplegia preceded seizures by several years have been reported [6]. Thus, future seizure occurrence cannot be excluded, and regular follow-up is warranted.

The diagnostic criteria proposed in 2005 allow the diagnosis of RE in the absence of seizures if progressive clinical and MRI changes are present. In this case, MRI progression was not evident at 3 and 7 months, possibly because early immunosuppressive therapy slowed disease progression [7]. Therefore, the absence of radiological progression does not exclude RE, and the clinical course and therapeutic response must also be considered. Although this case did not fully satisfy the revised Bien clinical diagnostic criteria for RE, the unilateral hemispheric atrophy together with inflammatory imaging findings suggested a Rasmussen-like process.

On the other hand, the patient’s responsiveness to immunosuppressive therapy raises the possibility of an alternative diagnosis, such as autoimmune encephalitis involving the basal ganglia. In the absence of histopathological confirmation through brain biopsy, both RE and autoimmune encephalitis remain viable diagnostic considerations. Therefore, long-term longitudinal follow-up with serial clinical and MRI evaluations will be essential to further clarify the diagnosis.

Movement disorders are rarely reported in RE, and parkinsonism has been documented only once in the literature [5]. To the best of our knowledge, this is the first reported case in Korea of adult-onset RE presenting with parkinsonian features as the initial manifestation. Notably, the symptoms persisted for a prolonged period without seizures. This case highlights the clinical rarity and diagnostic significance of atypical presentations of RE. Further investigations of similar cases may help clarify the clinical spectrum of adult-onset RE.

Supplementary Materials

Notes

Ethics Statement

The patient provided written informed consent form in accordance with the 2013 Declaration of Helsinki. The objectives and procedures of the study were approved by the Institutional Review Board of Eulji Medical Center (approval No. 2025-08-003).

Conflicts of Interest

The authors have no financial conflicts of interest.

Funding Statement

None

Acknowledgments

None

Author Contributions

Conceptualization: Sung Min Lim, Sangmin Park. Data curation: all authors. Investigation: Sung Min Lim. Supervision: Sangmin Park. Writing—original draft: Sung Min Lim, Sangmin Park. Writing—review & editing: all authors.

Figure 1.

Fluid-attenuated inversion recovery images show atrophy of the right cerebral cortex with subcortical hyperintense signals. Additionally, several hyperintense foci are seen in the right putamen, periventricular white matter, and centrum semiovale.

REFERENCES

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