72. LIMBIC-PREDOMINANT AMNESTIC NEURODEGENERATIVE SYNDROME PRESENTING AS VERY LATE-ONSET SCHIZOPHRENIA-LIKE PSYCHOSIS

Introduction

Limbic-predominant amnestic neurodegenerative syndrome (LANS) is a newly recognized neurologic disorder. The clinical symptoms of LANS overlap with Alzheimer’s disease but are differentiated by an older age at initial evaluation (> 80 years old), memory-predominant dysfunction, and slow clinical progression. In rare cases, it can present with neuropsychiatric symptoms and should be considered in the differential diagnosis of late-onset psychotic disorders in older adults.

Methods

We describe a case of LANS presenting with initial features of very late-onset schizophrenia-like psychosis (VLOSLP). We detail the clinical symptoms, neuropsychometric testing and neuroimaging.

Results

An 85 year-old female with no prior psychiatric history presented to clinic with a 9-month history of progressively worsening psychotic symptoms including auditory, visual, olfactory, and tactile hallucinations, and persecutory delusions. She did not have any negative symptoms and continued to function fairly well outside of anxiety related to her delusions. A screening cognitive exam revealed only mild deficits in memory. The patient underwent numerous evaluations including neuropsychometric testing, 48-hour EEG, and brain MRI, which were largely inconclusive or non-explanatory. FDG PET showed mild bilateral medial and inferior temporal hypometabolism. An evaluation with behavioral neurology revealed surface dyslexia and relatively weak semantic historical knowledge, which correlated with neuroimaging findings of right temporal hypometabolism. She was diagnosed with LANS, likely due to limbic-predominant age-related TDP-43 encephalopathy (LATE).

Conclusions

Symptoms of VLOSLP should raise suspicion for an underlying neurocognitive disorder, even in the absence of overt cognitive decline. VLOSLP may serve as an early or atypical psychiatric manifestation of a limbic-predominant amnestic neurodegenerative syndrome. These patients often present with circumscribed memory symptoms and relatively intact daily functioning, which can obscure the diagnosis of a neurodegenerative disorder. However, further investigation typically reveals impaired semantic memory, limbic hypometabolism, and absence of neocortical degeneration. Recognizing this relationship is crucial for guiding both diagnostic and therapeutic approaches and identifying patients at risk for progression to more pronounced cognitive decline or dementia.