Neuronal Intranuclear Inclusion Disease: A Rare Etiology for Rapidly Progressive Dementia

Neuronal intranuclear inclusion disease (NIID) is a rare neurodegenerative disorder pathologically characterized by localized neuronal loss, and presence of eosinophilic intranuclear inclusions in neurons and glial cells.

A 50-year-old man presented with rapidly progressive dementia, behavioral changes, gait disturbances, and incontinence of 3 months duration. His brain magnetic resonance imaging showed diffuse T2/FLAIR hyperintensity of basal ganglia, thalami, cerebral peduncles, ventral pons, and supratentorial white matter with a frontal predominance. Hyperintensity was noted along the corticosubcortical junction on diffusion-weighted images. NIID was suspected and the patient underwent triple biopsy of the sural nerve with adjacent skin and biceps biopsy. Biopsy revealed ubiquitin-positive intranuclear inclusions surrounding the myofibers, and vascular smooth muscles suggestive of NIID.

NIID is a rare neurodegenerative disorder usually diagnosed postmortem. The rectal and skin biopsy had proved helpful in antemortem diagnosis. We have increased the diagnostic armamentarium by showing the presence of intranuclear inclusions in smooth muscle cells of the muscle. Hence, a high degree of suspicion, magnetic resonance imaging features, with nerve/muscle/skin biopsy can help in diagnosis of NIID.