BRIDGING THE GAP BETWEEN NEUROLOGY AND PSYCHIATRY-ATYPICAL PRESENTATION OF COMMON NEURODEGENERATIVE DISORDERS: Session 418

Abstract It is increasingly recognized that there is significant heterogeneity in phenotype and clinical trajectories both in Alzheimer's as well as in Parkinson's disease. Up to 25% of Alzheimer's disease (AD) cases do not show the typical neuropathology. Recently subtypes and atypical non-amnestic AD presentations have been formalized in the International Working Group (IWG) clinical diagnosis criteria. Clinical diagnosis of atypical AD has significantly been improved by the availability of biomarkers, including cerebrospinal fluid levels of Aβ42, total tau (t-tau) and phosphorylated tau181 (p-tau), MRI volumetric estimation of hippocampal and medial temporal atrophy, and amyloid brain PET imaging. We will review the typical and atypical forms of AD from these varied perspectives to help improve diagnostic confidence among clinicians. Special attention will be given to language variant of Alzheimer's disease. A predominant deficit in the language domain is a key feature of primary progressive aphasia but language impairment is commonly present in Alzheimer's disease. International diagnostic criteria for PPA and its three variants (agrammatic, logopenic, semantic) were published relatively recently in 2011. Since then, studies have investigated the validity of these criteria in classifying patients which includes clinical symptoms, neurocognitive presentations, distinct MRI signatures, and neuropathological differences. In this session, we will review the subtypes of PPA using the above parameters to assist clinicians in diagnosis of these conditions. Special attention will be given of logopenic PPA a syndrome frequently seen in atypical Alzheimer's disease. Another common neurodegenerative disorder, Parkinson's disease (PD) conceptualized as predominantly movement disorder presents with myriad of atypical features predominantly psychiatric in nature. Psychosis is one of the most debilitating symptoms of PD, as it is an independent risk factor for nursing home placements, increased caregiver distress and mortality. Visual hallucinations are the most common psychotic manifestation in PD. Auditory, olfactory, tactile and gustatory hallucinations are infrequently found and usually coexist with visual ones. Delusions occur in about 5% of Parkinson's disease patients. Cognitive correlates of hallucinations and delusions appear to be different in PD. They may have distinct pathogenic mechanisms and possibly anatomical substrates. Global cognitive deficits including attention, frontal executive dysfunction, visuospatial abnormalities, language and verbal memory were associated with the presence of hallucinations in Parkinson's disease, but did not correlate with the presence of delusions. APOE and glucocerebrosidase gene (GBA) mutations and polymorphisms found to be associated with a distinct cognitive profile of changes characterized by greater impairment in working memory/executive function and visuospatial abilities in PD patients. During this session new findings on pathognomonic, cognitive and genetic correlates of psychosis in PD will be presented.