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Neuronal intranuclear inclusion disease (NIID) is a rare heterogenous neurodegenerative disorder characterized by eosinophilic intranuclear inclusions distributed throughout the central and peripheral nervous system. Herein we present a case of adult-onset NIID mimicking an acute-stroke, who developed characteristic imaging findings 5 years after initial presentation.   

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A 41-year-old female presented with headache and a right homonymous inferior quadrantanopsia.  MRI revealed a left temporo-parietal lesion with T2 FLAIR hyperintensity, cortical edema, and associated regions of cortical/subcortical diffusion restriction. She was treated as a subacute stroke, etiology undetermined. Interval imaging demonstrated multiple new foci of diffusion restriction within the left hemispheric lesion; this pattern of evolution was felt to be atypical for stroke and favored to be focal inflammatory encephalitis. Extensive investigations culminating in mitochondrial DNA/whole exome sequencing were normal. Repeat imaging 5 years after her initial presentation demonstrated new diffusion restriction in the bifrontal corticomedullary region. Given this new imaging finding NIID was considered and ultimately confirmed with skin biopsy.  

NIID is becoming increasingly recognized due to the advent of skin biopsy, and genetic testing for expansion of a trinucleotide (GGC) repeat in the 5' UTR of NOTCH2NLC. The hallmark of NIIDH is symmetric diffusion restriction of the corticomedullary junction, particularly in the frontal and parietal lobes similar to our case. Our study is the first to describe these changes 5 years from symptom onset (changes are characteristically seen within 1­–130 days of initial symptoms); we speculate these long-term changes are secondary to ongoing intracellular inclusion body accumulation. Episodic neurologic events (including stroke and encephalitic-like episodes) account for 30% of NIID but are prone to misdiagnosis. Given the advent of new targeted therapies (proof of concept gene-editing technology to repair CGG repeat sequences has been recently demonstrated) it is important to recognize NIID as a mimic of stroke/encephalitis.