Adult-Onset Neuronal Intranuclear Inclusion Disease Initially Manifesting as Bladder Dysfunction: A Case Report

Neuronal intranuclear inclusion disease (NIID) is a rare neurodegenerative disorder characterized by eosinophilic intranuclear inclusions and diverse clinical manifestations. In adults, NIID typically manifests as cognitive impairment, while autonomic dysfunction, such as bladder issues, is uncommon as an initial manifestation. We present a case of adult-onset NIID where bladder dysfunction preceded cognitive impairment by several years. A woman in her sixties experienced progressive urinary incontinence and voiding difficulties, necessitating intermittent self-catheterization. Early brain magnetic resonance imaging (MRI) revealed ribbonlike hyperintensity at the frontal corticomedullary junction on diffusion-weighted imaging, along with multifocal white matter lesions. However, no cognitive impairment was evident at that time. Subsequent cognitive decline progressed gradually. Further evaluation, including skin biopsy, showed ubiquitin-positive intranuclear inclusions, and genetic testing identified an abnormal guanine-guanine-cytosine (GGC) repeat expansion in the NOTCH2NLC gene, confirming the diagnosis of NIID. This case highlights that bladder dysfunction could precede cognitive impairment by years in adult-onset NIID. NIID should be considered in unexplained bladder dysfunction cases, particularly with suggestive MRI findings. Early recognition and minimally invasive skin biopsies can aid in prompt diagnosis.