Evaluation of predictors of mortality in frontotemporal dementia-methodological aspects

To retrospectively evaluate pre-diagnostic clinical features (predictors) of mortality in frontotemporal dementia (FTD). The main aim was to investigate if there were indications against interpreting missing data as signs of absence.

96 cases with FTD, here defined as Dementia in Pick's disease according to ICD-10. The predictors were behavioural/psychiatric features, language impairment and neurological deficits up to the date of diagnosis. Each predictor was rated as present (Yes), absent (No) or not recorded (Missing), and evaluated according to its distribution and mortality pattern: if a feature was not recorded because it was absent, the mortality of the Missing and the No-category should hypothetically be close. Statistical methods included Kaplan-Meier survival curves and Cox regression analyses.

Neurological deficits and language impairments were frequently recorded as present or absent, while non-recordings were more prevalent among the behavioural/psychiatric features. Some features were excluded as predictors because they showed too little variation. Analyses of the survival pattern indicated that in some features, the observations of the Missing-category could be interpreted as absence of the symptoms. In other features these observations had to be regarded as truly missing.

In the retrospective evaluation of predictors of mortality a method for treating missing data was applied. The interpretation of non-recordings as signs of absence was supported by the analyses of the survival patterns in some of the studied features. However, the study underscores the importance of systematic estimations of pre-diagnostic clinical features in dementia.