Transcranial magnetic stimulation for the treatment of pharmacoresistant nondelusional auditory verbal hallucinations in dementia

Transcranial magnetic stimulation and transcranial direct current stimulation: treatments for cognitive and neuropsychiatric symptoms in the neurodegenerative dementias?

Introduction

Two methods of non-invasive brain stimulation, transcranial magnetic stimulation (TMS) and transcranial direct current stimulation (tDCS), have demonstrable positive effects on cognition and can ameliorate neuropsychiatric symptoms such as depression. Less is known about the efficacy of these approaches in common neurodegenerative diseases. In this review, we evaluate the effects of TMS and tDCS upon cognitive and neuropsychiatric symptoms in the major dementias, including Alzheimer’s disease (AD), vascular dementia (VaD), dementia with Lewy bodies (DLB), Parkinson’s disease with dementia (PDD), and frontotemporal dementia (FTD), as well as the potential pre-dementia states of Mild Cognitive Impairment (MCI) and Parkinson’s disease (PD).

Methods

PubMed (until 7 February 2014) and PsycINFO (from 1967 to January Week 3 2014) databases were searched in a semi-systematic manner in order to identify relevant treatment studies. A total of 762 studies were identified and 32 studies (18 in the dementias and 14 in PD populations) were included.

Results

No studies were identified in patients with PDD, FTD or VaD. Of the dementias, 13 studies were conducted in patients with AD, one in DLB, and four in MCI. A total of 16 of the 18 studies showed improvements in at least one cognitive or neuropsychiatric outcome measure. Cognitive or neuropsychiatric improvements were observed in 12 of the 14 studies conducted in patients with PD.

Conclusions

Both TMS and tDCS may have potential as interventions for the treatment of symptoms associated with dementia and PD. These results are promising; however, available data were limited, particularly within VaD, PDD and FTD, and major challenges exist in order to maximise the efficacy and clinical utility of both techniques. In particular, stimulation parameters vary considerably between studies and are likely to subsequently impact upon treatment efficacy.

The contribution of transcranial magnetic stimulation in the diagnosis and in the management of dementia

Transcranial magnetic stimulation (TMS) is emerging as a promising tool to non-invasively assess specific cortical circuits in neurological diseases. A number of studies have reported the abnormalities in TMS assays of cortical function in dementias. A PubMed-based literature review on TMS studies targeting primary and secondary dementia has been conducted using the key words "transcranial magnetic stimulation" or "motor cortex excitability" and "dementia" or "cognitive impairment" or "memory impairment" or "memory decline". Cortical excitability is increased in Alzheimer's disease (AD) and in vascular dementia (VaD), generally reduced in secondary dementias. Short-latency afferent inhibition (SAI), a measure of central cholinergic circuitry, is normal in VaD and in frontotemporal dementia (FTD), but suppressed in AD. In mild cognitive impairment, abnormal SAI may predict the progression to AD. No change in cortical excitability has been observed in FTD, in Parkinson's dementia and in dementia with Lewy bodies. Short-interval intracortical inhibition and controlateral silent period (cSP), two measures of gabaergic cortical inhibition, are abnormal in most dementias associated with parkinsonian symptoms. Ipsilateral silent period (iSP), which is dependent on integrity of the corpus callosum is abnormal in AD. While single TMS measure owns low specificity, a panel of measures can support the clinical diagnosis, predict progression and possibly identify earlier the "brain at risk". In dementias, TMS can be also exploited to select and evaluate the responders to specific drugs and, it might become a rehabilitative tool, in the attempt to restore impaired brain plasticity.