Neuronal intranuclear inclusion disease (NIID) is a rare slowly progressive neurodegenerative disorder that is characterized pathologically by the presence of eosinophilic intranuclear inclusions. NIID is a heterogeneous disease with diverse clinical manifestations, making diagnosis difficult. Here, we analyzed the clinical, pathological, and radiological features of Chinese NIID patients to improve our understanding of NIID.

A total of 17 patients with sporadic NIID were recruited from the Ruijin Hospital Database between 2014 and 2021. Clinical patient information and brain MRI data were collected. All of the patients underwent standard skin biopsy procedures.

The average age of onset for symptoms was 60.18 years, and the average duration of illness was 4.06 years. All patients were diagnosed with NIID due to the presence of intranuclear inclusions confirmed by skin biopsy. Tremor was the most common initial symptom. The average ages at onset and at diagnosis were both lower in patients with tremor than in patients without tremor. NIID may be a systemic disease that affects multiple organs, for one patient had a history of chronic renal insufficiency for more than 10 years. In addition to high-intensity U-fibers signals on diffusion-weighted imaging, there were several other MRI findings, such as focal leukoencephalopathy and cortical swelling. Encephalitic episodes followed by reversible leukoencephalopathy was another important imaging feature of NIID.

The clinical manifestations of NIID are highly variable. Tremor may be the most common initial symptom in certain cohorts. Encephalitic episodes followed by reversible asymmetric leukoencephalopathy may also indicate this disease.