A 64-year-old man was admitted to the hospital owing to sudden onset of involuntary and irregular movements of his left limbs in November 2021. Over the past 9 years, he had episodic fever and confusion once or twice a year, accompanied by a progressive cognitive impairment. He was hospitalized twice with the presence of encephalitis-like attack in 2012 and 2018, respectively. A relative had a similar history of encephalitis-like attack without clear diagnosis. On admission, results of general physical examination were normal. Neurological examination revealed miosis, postural tremors of hands, loss of tendon reflexes, and left hemichorea. The results of routine laboratory tests, such as blood lactate, autoantibodies, and blood biochemistry, were within normal limits. Repeated analysis of cerebrospinal fluid revealed a marginal increase in protein level with a normal cell count and glucose level. Brain magnetic resonance imaging (MRI) performed in 2012 indicated diffuse cortical injury in the right occipito-parieto-temporal insular lobes, with high signals on both diffusion-weighted imaging (DWI) and apparent diffusion coefficient (ADC) sequences (Figure 1A). Postcontrast T1-weighted imaging showed linear enhancement along the surface of the cortex (Figure 1B). Brain MRI performed in 2018 showed a similar cortical lesion in the left occipito-parieto-temporal insular lobes. On this admission, brain MRI performed 5 days after the presence of hemichorea showed high signals in the right globus pallidus on DWI sequence (Figure 2A) but isointensity on ADC sequence (Figure 2B). Neither muscle biopsy nor mitochondrial genome sequencing suggested any mitochondrial diseases. However, skin biopsy revealed eosinophilic inclusions positive for anti-p62 in the ductal epithelial cells of sweat glands. In addition, an expansion of 108 GGC repeated in the 5′-untranslated region of the NOTCH2NLC gene was detected by fluorescence amplicon length analysis polymerase chain reaction, confirming the diagnosis of neuronal intranuclear inclusion disease (NIID). A follow-up MRI performed 4 months after the hemichorea attack showed the lesion in the right basal ganglia appeared isointense on DWI sequence, but hypointense on ADC sequence.