Overflow urinary incontinence as an early manifestation of neuronal intranuclear inclusion disease (NIID): a case report

BACKGROUND: Neuronal intranuclear inclusion disease (NIID) is a rare neurodegenerative disorder with highly heterogeneous clinical manifestations, often leading to misdiagnosis. Urinary incontinence as the initial and predominant symptom of NIID has rarely been reported. CASE PRESENTATION: A Chinese male in his early seventies presented with an 8-year history of nocturnal urinary incontinence and a 4-year history of progressive memory loss. Detailed clinical, neuroimaging, electrophysiological, and genetic assessments were performed. Magnetic resonance imaging (MRI) showed high-intensity signals along the corticomedullary junction on diffusion-weighted imaging (DWI). Electrophysiological studies indicated peripheral neuropathy in all four limbs. Genetic analysis via polymerase chain reaction (PCR) combined with capillary electrophoresis identified a GGC repeat expansion (115 repeats) in the 5' untranslated region (5' UTR) of the NOTCH2NLC gene, confirming the diagnosis of NOTCH2NLC-associated NIID. CONCLUSION: This case highlights the diagnostic challenges of NIID presenting primarily with overflow urinary incontinence. It emphasizes the importance of considering NIID in patients with unexplained urinary dysfunction accompanied by cognitive decline, and confirms that early genetic testing is essential for accurate diagnosis and differential identification from other neurodegenerative diseases.