Estimating severity of illness and disability in Frontotemporal Dementia: Preliminary analysis of the Dementia Disability Rating (DDR)

Current measures of severity and disability do not stage or track the progression of disability in frontotemporal dementia (FTD) well. We investigated the reliability of the newly developed Dementia Disability Rating (DDR) in the measurement and staging of illness severity in FTD and dementia of the Alzheimer type (DAT). We studied 48 consecutive patients of the Johns Hopkins FTD and Young-Onset Dementias Clinic, with diagnoses of DAT, FTD, vascular dementia and "other" cognitive disorder (CDNOS). Cases were scored on the CDR and DDR by three trained raters, based on neuropsychiatric examinations performed at first visit and other assessments performed within the preceding year. Consensus ratings were assigned in conference. Inter-rater correlations of DDR sum of ranks scores for DAT ranged from 0.88 to 0.91, for FTD 0.89-0.96 and for CDNOS 0.85-0.97. Similar correlations were observed of the CDR sum of rank scores for DAT and FTD. Correlations of DDR summary scores for DAT were 0.67-0.91 and for FTD 0.79-0.91, as compared to CDR data: 0.87-0.92 (p<0.0001) and 0.80-0.93 (p<0.0001) for DAT and FTD respectively. In DAT patients the correlation between CDR and DDR summary scores was higher than in FTD patients, whereas correlations based on sum of ranks scores were high in both groups. These preliminary data indicate the DDR measures disability in DAT and FTD, with reliability comparable to the CDR. Convergent validity was demonstrated for the DDR.