Major depressive episodes are characteristic of both Unipolar Depression (UPD) and Bipolar Disorder (BD). Cognitive impairment is a well documented finding in such episodes. Wide-ranging cognitive deficits have been reported in UPD patients, including psychomotor, attention, memory and executive functions. BD patients were found impaired in attention capacity, memory and learning deficits. Distinguishing BD from UPD patients on the basis of cognitive impairment requires additional research.

Our objective was to clarify differences in cognitive functioning between UPD and BD patients during an acute depressive episode.

A better understanding of the cognitive impairments in each disorder, may significantly improve early diagnosis in acute depressed patients, in cases where it is unclear whether the patient presents UPD or BD.

Participants were 128 acute depressive outpatients, 87 had UPD and 41 had BD. Patients were assessed using Hamilton depression rating scale; Clinical Global Impression severity scale; Hamilton Anxiety Depression Survey; Beck Depression Inventory and Cambridge Neuropsychological Test Automated Battery (CANTAB). We used statistical modeling via logistic regression, to differentiate between UPD vs. BD, by means of their cognitive functions.

Significant differences between the two groups were found in several domains: visual memory, working memory and sustained attention. The predictive model that was constructed has a discriminatory power as measured by the area under the ROC curve of 0.76.

UPD and BD patients present different cognitive impairments during acute depression. Our model may help to predict the underlying mental disorder, and thus facilitate earlier initiation of proper treatment.