Original article
Spatial working memory in euthymic lithium-treated patients with bipolar disorder

The aim of the study was to assess spatial working memory using Spatial Working Memory Test (SWM) and Spatial Span (SSP) from Cambridge Automated Neuropsychological Test Battery (CANTAB) in a group of euthymic bipolar patients on prophylactic lithium therapy.

Material and methods: Sixty bipolar patients in remission lasting for at least 4 months and 84 healthy controls entered the study. Duration of illness was at least 5 years and prophylactic treatment lasted for at least 2 years. Mental state of patients was assessed used using Hamilton Depression Rating Scale (HDRS), and Young Mania Rating Scale (YMRS). All included bipolar patients met criteria of remission defined as HAMD < 8 and YMRS < 6 points.

Results: Bipolar patients performed significantly worse on SWM for between search errors and strategy as well as on SSP compared to healthy controls. The association between tests results and lithium prophylactic efficacy was also found. Lithium non-responders scored significantly worse on SWM than healthy controls. Excellent lithium responders showed similar results on SSP to those of controls, and remaining patients groups scored significantly worse than controls. Between search errors correlated with the patients’ age, education level and duration of illness, and SWM strategy use and SSP scores were associated with duration of illness and number of affective episodes.

Conclusions: The results point to the deficits in spatial working memory in euthymic bipolar patients and to the association of these deficits with lithium prophylactic efficacy.