Total sleep deprivation and light therapy relieve depression in bipolar patients but do not improve overall cognitive function, according to an Italian study published in the Journal of Affective Disorders.
In addition, bipolar patients "do not experience the well-known worsening of performance observed in healthy controls after sleep loss," said Sara Poletti, Ph.D., of the Scientific Institute and University Vita-Salute San Raffaele Turro, Milan, and her associates (J. Affect. Disord. 2014;156:144-9 [doi:10.1016/j.jad.2013.11.023]).
The investigators administered the Brief Assessment of Cognition in Schizophrenia (BACS) to 100 depressed bipolar I patients (DSM-IV) and 100 healthy controls, and then retested 42 subjects with bipolar disorder who underwent total sleep deprivation (TSD) and light therapy (LT), during which they were kept awake for three 36-hour periods over the course of a week, with bright lights shone on them for 30 minutes at 3 a.m. on TSD nights and in the morning after recovery sleep. The Hamilton Depression Rating Scale (HDRS) was administered to assess depression.
The mean age was 47 years in the bipolar group and 44 years in the control group. Both groups were made up of a majority of women. A quarter of the patients with bipolar disorder reported previous psychotic symptoms. Most of the TSD/LT patients were taking lithium, and some were taking other mood stabilizers, benzodiazepines, and antidepressants.
As expected from previous investigations, the 100 bipolar patients had significantly lower baseline cognitive function scores, showing impairment in verbal memory, working memory (digit sequencing), psychomotor coordination (token motor task), verbal fluency, selective attention (symbol coding), and executive function (Wisconsin Card Sorting Test).
Also in keeping with past studies, TSD/LT treatment caused an overall significant decrease in HDRS scores: 31 of the patients with bipolar (74%) achieved the strict remission criterion of HDRS score of less than 8 at day 7 and could be rated as full responders to treatment.
Regarding cognitive function, TSD and light therapy "showed a significant difference only for symbol coding (P less than 0.004). No significant differences were found for the remaining variables," Dr. Poletti and her associates said.
"Although most of the patients responded to TSD treatment reporting a clinical improvement of depressive symptomatology, cognitive deficits persisted in almost each function. The only improvement we observed was in symbol coding, confirming a positive effect of TSD on speed-of-information processing in bipolar patients," they wrote.
Also "in agreement with the literature, we found that as medication load decreases, cognitive performance improves. However, medication effects alone are not likely to fully account for the deficits described in these patients. We can hypothesize that TSD and LT act on cognitive functions through their effect on brain structures and neurotransmitter system[s]. Studies are needed to understand if remediation strategies such as those used for schizophrenia treatment could be introduced for bipolar patients," the investigators said.
Among the study limitations is that "the use and reporting of medications varied between patients, and it was very difficult to control for the potentially negative effect of medication on neurocognitive function, especially as the control group was not taking any medication," Dr. Poletti and her associates noted.
The study received no outside funding. The investigators said that they had no financial conflicts.