Ishihara test performance and dementia

Ishihara trail-tracing (TT) and number-naming (NN) tests were administered to a clinical sample of 378 demented patients. Error counts on TT and NN tests were best fit by a negative binomial (overdispersed Poisson) distribution. TT, NN, and combined (TT + NN) error counts were regressed on patient characteristics (sex, age, and education), severity of cognitive impairment (Mini-Mental State Exam: MMSE), dementia stage (Clinical Dementia Rating: CDR), etiology, onset age, and symptom duration in a negative binomial generalized linear model. Patient characteristics, onset age, and symptom duration had no significant effects on any error count. The effects of MMSE, CDR, and etiology, on the other hand, were highly significant and appear to help discriminate vascular dementia from Alzheimer's disease. MMSE (which taps cognitive skills) correlated with both TT and NN errors. CDR (which taps both cognitive and functional skills) correlated only with TT errors and dementia etiology correlated only with NN errors. These distinct correlational patterns reflect differences between the TT and NN tasks (i.e., trail-tracing vs. number-naming) related to specific brain loci and associated functions. This aspect of the phenomenon suggests that Ishihara tests have useful clinical applications in dementia.