Standardizing “Rapid”

BACKGROUND AND OBJECTIVES: Rapidly progressive dementia (RPD) accounts for 3%-4% of dementia cases yet presents a disproportionate clinical challenge given the wide differential diagnosis and the need to quickly identify potentially treatment-responsive causes. The lack of a standardized definition of RPD challenges generalization of published findings and precludes multisite studies. We sought to determine whether a standardized definition, based on the Clinical Dementia Rating (CDR), could reliably distinguish individuals with a broad spectrum of causes of RPD early in the symptomatic course. METHODS: tests (binary), respectively. Our definition of RPD was compared against definitions identified through a scoping review conducted using a validated 6-stage approach. RESULTS: < 0.001). Our scoping review identified 22 studies that applied 10 distinct definitions of RPD. Uniquely, our CDR-based definition clearly distinguished individuals with a broad spectrum of causes of RPD, assessed across multiple sites/settings, supporting early diagnosis with minimal resource requirements. DISCUSSION: The CDR-based definition of RPD effectively identified individuals with a broad spectrum of causes of RPD early in the symptomatic course. The need for training and time to reliably administer the CDR may limit application of the proposed definition of RPD. Validation in additional cohorts is required to support generalizability.