A comprehensive review of transcranial magnetic stimulation in secondary dementia

Abstract

Although primary degenerative diseases are the main cause of dementia, a non-negligible proportion of patients is affected by a secondary and potentially treatable cognitive disorder. Therefore, diagnostic tools able to early identify and monitor them and to predict the response to treatment are needed. Transcranial magnetic stimulation (TMS) is a non-invasive neurophysiological technique capable of evaluating in vivo and in “real time” the motor areas, the cortico-spinal tract, and the neurotransmission pathways in several neurological and neuropsychiatric disorders, including cognitive impairment and dementia. While consistent evidence has been accumulated for Alzheimer’s disease, other degenerative cognitive disorders, and vascular dementia, to date a comprehensive review of TMS studies available in other secondary dementias is lacking. These conditions include, among others, normal-pressure hydrocephalus, multiple sclerosis, celiac disease and other immunologically mediated diseases, as well as a number of inflammatory, infective, metabolic, toxic, nutritional, endocrine, sleep-related, and rare genetic disorders. Overall, we observed that, while in degenerative dementia neurophysiological alterations might mirror specific, and possibly primary, neuropathological changes (and hence be used as early biomarkers), this pathogenic link appears to be weaker for most secondary forms of dementia, in which neurotransmitter dysfunction is more likely related to a systemic or diffuse neural damage. In these cases, therefore, an effort toward the understanding of pathological mechanisms of cognitive impairment should be made, also by investigating the relationship between functional alterations of brain circuits and the specific mechanisms of neuronal damage triggered by the causative disease. Neurophysiologically, although no distinctive TMS pattern can be identified that might be used to predict the occurrence or progression of cognitive decline in a specific condition, some TMS-associated measures of cortical function and plasticity (such as the short-latency afferent inhibition, the short-interval intracortical inhibition, and the cortical silent period) might add useful information in most of secondary dementia, especially in combination with suggestive clinical features and other diagnostic tests. The possibility to detect dysfunctional cortical circuits, to monitor the disease course, to probe the response to treatment, and to design novel neuromodulatory interventions in secondary dementia still represents a gap in the literature that needs to be explored.

Sex differences in mild vascular cognitive impairment: A multimodal transcranial magnetic stimulation study

“…In the last 20 years, TMS has been applied in patients with dementia, allowing the identification of potential markers or predictors of cognitive decline. As recently reviewed, TMS provides insights into the pathophysiology, progression, and response to treatment in different forms of dementia, including AD and other degenerative disorders [45], as well as in a number of secondary dementias [46]. Although a single TMS index offers low specificity, the use of a panel of measures can support the clinical diagnosis and possibly predict progression.…”

Celiac Disease and Neurological Manifestations: From Gluten to Neuroinflammation

“…Within common neurophysiological methods, transcranial magnetic stimulation (TMS) is a technique able to non-invasively assess, in “real-time” and in vivo, the functional integrity of the central motor pathway and both intracortical and intercortical excitability, as well as provide insights on the neurochemical changes involved in the different neurological, neuropsychiatric, and systemic disorders causing cognitive impairment [ 141 , 142 , 143 ]. The assessment of the cortico-spinal conductivity and cortical excitation state is carried out through the application of single- or paired-pulse TMS at an adequate stimulation intensity over the primary motor cortex (M1), thus generating a motor-evoked potential (MEP), which may be easily recorded from specific muscles contralaterally to the stimulation side [ 144 ], and that can be repeated over time to monitor disease progression [ 145 ].…”

Non-invasive brain stimulation therapy on neurological symptoms in patients with multiple sclerosis: A network meta analysis

“…In addition, the heterogeneity of clinical and radiological features of MS makes it difficult to determine which distinctive NIBS pattern would be most suitable for all patients. MS symptoms and disabilities are associated with asymmetric interhemispheric brain excitability ( 62 ), typically caused by neuroinflammation at its onset or degeneration as it progresses ( 63 ). Both cortical demyelination and subcortical myelination contribute to motor cortex excitability, resulting in variability in plasticity-inducing effects of NIBS between individuals ( 64 , 65 ).…”