Abstract and Introduction
Abstract
Background and Hypothesis: Impaired insight into the illness and its consequences is associated with poor outcomes in schizophrenia. While transcranial direct current stimulation (tDCS) may represent a potentially effective treatment strategy to relieve various symptoms of schizophrenia, its impact on insight remains unclear. To investigate whether tDCS would modulate insight in patients with schizophrenia, we undertook a meta-analysis based on results from previous RCTs that investigated the clinical efficacy of tDCS. We hypothesize that repeated sessions of tDCS will be associated with insight improvement among patients.
Study Design: PubMed and ScienceDirect databases were systematically searched to identify RCTs that delivered at least 10 tDCS sessions in patients with schizophrenia. The primary outcome was the change in insight score, assessed by the Positive and Negative Syndrome Scale (PANSS) item G12 following active tDCS sessions as opposed to sham stimulation. Effect sizes were calculated for all studies and pooled using a random-effects model. Meta-regression and subgroup analyses were conducted.
Study Results: Thirteen studies (587 patients with schizophrenia) were included. A significant pooled effect size (g) of −0.46 (95% CI [−0.78; −0.14]) in favor of active tDCS was observed. Age and G12 score at baseline were identified as significant moderators, while change in total PANSS score was not significant.
Conclusions: Ten sessions of active tDCS with either frontotemporoparietal or bifrontal montage may improve insight into the illness in patients with schizophrenia. The effect of this treatment could contribute to the beneficial outcomes observed in patients following stimulation.
Introduction
Lack of patient insight into the illness is a key characteristic of many psychiatric disorders, including bipolar disorder,[1] obsessive-compulsive disorder,[2] and dementias.[3] Among patients with schizophrenia, the estimated prevalence of poor insight, corresponding to a general unawareness of illness, can be up to 50%.[4,5] Insight deficit includes a lack of awareness of the symptoms of the illness, the need for and willingness to undergo treatment, and the consequences of the illness on the patient's life.[6] Poor insight has been regularly associated with negative attitudes toward medication[7] and nonadherence to antipsychotic treatment.[8–11] Treatment nonadherence in schizophrenia represents a heavy economic cost, estimated between $13.92 and $18.36 million a year in the United States,[12] because it increases the risk of relapse, rehospitalization rates, and suicide attempts.[12,13] Poor insight is directly associated with a higher risk of relapse,[14] which further emphasizes the importance of fostering better insight into the illness. Unfortunately, available treatments such as antipsychotic medication and psychotherapy provide either little or no improvement in patients' insight into their illness.[15]
Transcranial direct current stimulation (tDCS) is a safe, low-cost tool for modulating the activity and connectivity of targeted brain regions and related neural networks.[16,17] tDCS consists of applying weak electric currents through two electrodes placed over the scalp, with polarity-dependent effects on cortical excitability: Currents entering the brain at the anode site are thought to increase cortical excitability while currents exiting the brain at the cathode site are thought to decrease cortical excitability.[18] For clinical purposes, repeated sessions of tDCS show promising results in alleviating some of the symptoms of schizophrenia and may also improve cognition in these patients.[19] The means by which tDCS alleviates symptoms remain unclear, and one can hypothesize that a beneficial effect on metacognitive processes, and especially on insight capacities, could be considered to explain tDCS's clinical effect because insight impairments have been associated with alteration in the activity of brain regions regularly targeted by tDCS (frontal and temporoparietal regions for example).[20] Nevertheless, to date, only 5 articles from 3 different randomized controlled trials (RCTs) have studied the effect of tDCS on insight in patients with schizophrenia using different scales;[21–25] thus, drawing firm conclusions remains difficult.[26] An underutilized source of informative data on the impact of tDCS on insight is a widely used psychiatric assessment scale:[27] the Positive and Negative Syndrome Scale (PANSS) and its item G12.[28] This item assesses the lack of judgment and insight into the illness using a 7-level scale (ranging from 1, no impairment, to 7, extreme lack of insight). Gathering these often-unexamined data would provide a new source of evidence in establishing the potential benefits of treatment with tDCS on insight.
Because insight deficits are a major problem in the management of patients with schizophrenia, we conducted a systematic review and meta-analysis of randomized, sham-controlled clinical trials to evaluate the association between tDCS treatment and improvement in PANSS G12 scores in patients with schizophrenia. We hypothesized that, compared with sham tDCS, active tDCS will be associated with a decrease in G12 scores, which corresponds to an improvement in patient insight.
Schizophr Bull. 2022;48(6):1284-1294. © 2022 Oxford University Press
