Cognitive deficits stable across bipolar disease course

By Sarah Pritchard, medwireNews Reporter

The cognitive deficits experienced by patients with bipolar disorder are relatively stable across the disease course, show findings from a meta-analysis involving 14 studies.

The researchers found no significant differences in 14 cognitive variables examined throughout the analyses, including immediate verbal memory, verbal fluency, processing speed and cognitive flexibility.

Sergio Strejilevich (Favaloro University, Buenos Aires, Argentina) and co-workers believe their work “contributes to [...] knowledge on the longitudinal trajectory of cognitive deficits as a synthesis of the evidence available to date.” Their findings do “not support the hypothesis of a progressive decline of cognitive effects”, they add.

The team employed two different meta-analytic approaches, first to assess all longitudinal studies retrieved by a criteria-based internet search, and second to only assess the studies from the search that included a healthy control group at baseline and follow-up.

An average of 152 patients were followed up for an average 4.62 years in the 12 longitudinal studies, while an average of 233 patients were followed up for 2.20 years and compared with 165 healthy controls in the six studies of this type.

A total of 14 neuropsychological measurements were taken in the longitudinal studies, including the National Adult Reading Test to measure Crystalised Intelligence, the Trail Making Test part A to assess attention and the California Verbal Learning Test to assess immediate verbal memory. The patient–control studies examined phonemic/verbal fluency, backwards digit span for processing speed and the Stroop test for executive control. The researchers calculated a global cognitive score, comprising all measurements, for all studies.

Strejilevich and colleagues observed no significant differences in test–retest effect size for any of the variables analysed in the longitudinal studies, indicating stable findings over time. The distribution of effect sizes in the longitudinal studies was “highly homogeneous” for 10 of the variables including Crystalised Intelligence, phonemic fluency and backward and forward digit span.

There were also no significant test–retest differences in the patient–control studies, the team reports in the Journal of Affective Disorders.

The team cautions that short follow-up times, differences in medication variables, a lack of mood rating scales at baseline and follow-up and attrition rates could limit the interpretability of their findings, but that they could contribute to future studies “by providing a clue about the follow-up time needed to evaluate a potential cognitive decline.”

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