Pathological background of subcortical hyperintensities on diffusion-weighted images in a case of neuronal intranuclear inclusion disease

Aims: Neuronal intranuclear inclusion disease (NIID) is a rare neurodegenerative disorder with eosinophilic intranuclear inclusion bodies. The variable symptoms of NIID increase the difficulty in an antemortem diagnosis. NIID shows leukoencephalopathy on brain magnetic resonance imaging MRI, but the significance of the radiological findings have not been clarified. Methods: We examined an autopsied case of NIID with subcortical linear hyperintensities on diffusion weighted imaging (DWI) and leukoencephalopathy on fluid attenuation inversion recovery (FLAIR) imaging. Semiquantitative analysis was performed by merging coronal sections of DWI and identical hematoxylineosin (H & E) stained brain specimens. The severity of spongiotic changes, the common pathological findings of NIID, were quantified and compared with MRI lesions classified by DWI signals. Results: The white matter showed diffuse myelin pallor, and multiple focal spongiotic changes were present in the subcortical white matter proximal to the Ufibers. Spongiotic changes were restricted in the lesions with subcortical linear DWI high signals. Conclusion: Subcortical DWI high signals in NIID strongly correlate with pathological spongiotic changes of NIID. Subcortical spongiotic changes may be a characteristic finding of NIID.