A Case of Neuronal Intranuclear Inclusion Disease Presenting with Episodic Visual Blurring: A Case Report

Background: Neuronal intranuclear inclusion disease (NIID) is a rare, progressive neurodegenerative disorder characterized by the presence of eosinophilic hyaline intranuclear inclusions in both the nervous system and visceral organs. Clinical presentation is highly heterogeneous, often including cognitive impairment, movement disorders, autonomic dysfunction, and episodic encephalopathy. Episodic visual blurring as a sole or predominant initial symptom is exceedingly uncommon and poses a significant diagnostic challenge. Case Presentation: A 67-year-old male amateur cyclist presented with a 7-year history of recurrent episodes of bilateral visual blurring, consistently triggered by prolonged, strenuous exercise (e.g., cycling over 110 km). Symptoms resolved completely after several hours of rest. Initial ophthalmological and neurological workups were inconclusive. Over the years, serial brain diffusion-weighted imaging (DWI) revealed the characteristic corticomedullary "ribbon sign." A skin biopsy revealed intranuclear inclusions in sweat gland duct epithelial cells. Ultimately, genetic analysis confirmed a pathological GGC repeat expansion (approximately 114 repeats) in the NOTCH2NLC gene, diagnostic of NIID. Conclusion: This case underscores the diagnostic challenge of NIID, particularly when it presents with isolated episodic symptoms triggered by physical exertion. It highlights the importance of considering NIID in the differential diagnosis of transient neurological episodes and demonstrates the critical role of genetic testing for definitive diagnosis.