Transcranial magnetic stimulation in multiple system and late onset cerebellar atrophies

Abnormal cortical excitability in patients with spinocerebellar ataxia type 12

BACKGROUND

Spinocerebellar ataxia type 12 (SCA-12) is an uncommon autosomal dominant cerebellar ataxia characterized by action tremors in the upper limbs, dysarthria, head tremor, and gait ataxia. We aimed to evaluate the motor cortical excitability in patients with SCA-12 using transcranial magnetic stimulation (TMS).

METHODS

The study was done in the department of Neurology at the National Institute of Mental Health and Neuro Sciences (NIMHANS), Bangalore. Nine patients with SCA-12 (2 females) and 10 healthy controls (2 females) were included in the study. TMS was performed in all the subjects and various parameters such as resting motor threshold (RMT), central motor conduction time (CMCT) and contralateral silent period (cSP) were recorded. The left motor cortex was stimulated and the recording was done from right first dorsal interossei muscle. The severity of ataxia was assessed using the scale for assessment and rating in ataxia (SARA).

RESULTS

The mean age of the patients was 58.11 ± 7.56 years mean age at onset: 51.67 ± 4.18 years. The mean duration of illness was 9.44 ± 4.88 years. The mean SARA score was 13.83 ± 3.60. Patients with SCA-12 had significantly increased RMT (88.80 ± 12.78 %) compared to HC (44.90 ± 9.40 %, p < 0.05). A significantly prolonged CMCT was observed in patients (13.70 ± 2.52 msec) compared to HC (7.31 ± 1.21 msec, p < 0.05). In addition, cSP was significantly increased in SCA-12 patients (144.43 ± 25.79 msec) compared to HC (82.14 ± 28.90 msec, p < 0.05).

CONCLUSIONS

Patients with SCA-12 demonstrate a reduced cortical excitability and increased cortical inhibition suggesting an increase in the GABAergic neurotransmission.

Early recognition and diagnosis of multiple system atrophy: best practice and emerging concepts

Introduction: Multiple system atrophy (MSA) is a progressive degenerative disorder of the central and autonomic nervous systems characterized by parkinsonism, cerebellar ataxia, dysautonomia, and pyramidal signs. The confirmatory diagnosis is pathological, but clinical-diagnostic criteria have been developed to help clinicians. To date, the early diagnosis of MSA is challenging due to the lack of reliable diagnostic biomarkers.Areas covered: The authors reappraised the main clinical, neurophysiological, imaging, genetic, and laboratory evidence to help in the early diagnosis of MSA in the clinical and in the research settings. They also addressed the practical clinical issues in the differential diagnosis between MSA and other parkinsonian and cerebellar syndromes. Finally, the authors summarized the unmet needs in the early diagnosis of MSA and proposed the next steps for future research efforts in this field.Expert opinion: In the last decade, many advances have been achieved to help the correct MSA diagnosis since early stages. In the next future, the early diagnosis and correct classification of MSA, together with a better knowledge of the causative mechanisms of the disease, will hopefully allow the identification of suitable candidates to enroll in clinical trials and select the most appropriate disease-modifying strategies to slow down disease progression.

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.

Assessment of cortico-spinal tract impairment in multiple system atrophy using transcranial magnetic stimulation

OBJECTIVE

Among Parkinsonian syndromes, pyramidal signs suggesting cortico-spinal impairment are a hallmark of multiple system atrophy (MSA). Although it is crucial to diagnose correctly this disease to choose the appropriate treatment, the available diagnostic criteria lack sensitivity. Cortical excitability patterns assessed by transcranial magnetic stimulation (TMS) do not differentiate Parkinsonian disorders. TMS using triple stimulation technique (TST) accurately detects cortico-spinal impairment. We hypothesized that this technique could detect such impairment in MSA patients.

METHODS

The TST was applied along with single and paired-pulse TMS to 31 patients fulfilling the diagnostic criteria for MSA-P (n=10), MSA-C (n=4), progressive supranuclear palsy (PSP; n=6) and Idiopathic Parkinson's disease (IPD; n=11) and 11 control subjects.

RESULTS

Single and paired-pulse TMS patterns did not differ between any patient group. The TST pattern was abnormal in five MSA-P, one MSA-C and one PSP patients but not in IPD patients or controls. The mean TST ratio for MSA-P (86.6%) was significantly different from IPD (99.1%; p<0.05) whereas ratios for MSA-C (92.1%) and PSP (93.3%) were not different from IPD or controls (99.5%).

CONCLUSIONS

These results suggest that TST is effective to assess cortico-spinal impairment in MSA.

SIGNIFICANCE

TST might be useful for the diagnosis of atypical Parkinsonism.

Abnormal responses to repetitive transcranial magnetic stimulation in multiple system atrophy

We studied the response of the motor cortex to brief trains of suprathreshold repetitive transcranial magnetic stimulations (rTMS) in patients with the Parkinson-variant of multiple system atrophy (MSA-P) and compared it to patients with idiopathic Parkinson's disease (PD) and healthy controls. Eight subjects were studied in each group, and patients were matched for disease severity as assessed by Hoehn & Yahr stages. rTMS was delivered at rest and during low-level contractions in trains of 10 stimulations at 5 Hz, and stimulation intensity was set to result in an motor evoked potential (MEP) in the first dorsal interosseus muscle of 0.5 to 1.0 mV. In MSA-P, MEP amplitude at rest was already reduced after the second stimulus and remained so, while it did not change in PD and controls. During contraction, MEP size did not change during the train in any group. The silent period that followed the last stimulus was of similar duration as the first stimulus in MSA-P, but was increased in PD and controls. These findings indicate that abnormal inhibition occurs within the motor cortex in MSA-P, despite dopaminergic treatment and indicate differences in cortical dysfunction between MSA-P and PD. We suggest that these abnormalities reflect the motor cortex pathology found in MSA-P.

Applications of transcranial magnetic stimulation in movement disorders

The author reviews the applications of transcranial magnetic stimulation (TMS) in a series of movement disorders--namely, Parkinson's disease, corticobasal degeneration, multiple system atrophy, progressive supranuclear palsy, essential tremor, dystonia, Huntington's chorea, myoclonus, the ataxias, Tourette's syndrome, restless legs syndrome, Wilson's disease, Rett syndrome, and stiff-person syndrome. Single- and paired-pulse TMS studies have been done mainly for pathophysiologic purposes. Repetitive TMS has been used largely for therapy. Many TMS abnormalities are seen in the different diseases. They concur to show that motor cortical areas and their projections are the main target of the basal ganglia dysfunction typical of movement disorders. Interpretation has not always been clear, and sometimes there were discrepancies and contradictions. Largely, this may be the result of the extreme heterogeneity of the methods used and of the patients studied. It is premature to give repetitive TMS a role in treatment. Overall, however, TMS gives rise to a new, outstanding enthusiasm in the neurophysiology of movement disorders. There is reason to predict that TMS, with its continuous technical refinement, will prove even more helpful in the near future. Then, research achievements are reasonably expected to spill over into clinical practice.

Changes of cortical excitability of human motor cortex in spinocerebellar ataxia type 2. A study with paired transcranial magnetic stimulation

The aim of this study was to evaluate motor cortex excitability in spinocerebellar ataxia type 2 (SCA2). Cortical silent period (CSP), motor thresholds, and intracortical inhibition and facilitation by paired transcranial magnetic stimulation (TMS) were investigated in 18 SCA2 patients and in 20 controls. The mean CSP duration and motor threshold after TMS were significantly increased in the patient group. Intracortical inhibition by paired TMS at short interstimulus intervals (ISIs) showed no significant differences between patients and controls; at longer ISIs, the expected facilitation of test responses, observed in control subjects, resulted significantly less marked in SCA2 patients at all the tested intervals. Our findings extend previous findings on cerebellar dysfunctions of varying aetiologies by investigating intracortical excitability in SCA2. In addition, this study demonstrates that the cortical excitability involvement found in SCA2 is independent on the cytosine-adenine-guanine repeat expansion. The neurophysiological alterations seen in our patients relate to the worsening of general clinical condition. Thus, we might speculate that changes of motor cortex excitability in SCA2 represent a slow neurodegenerative process characterized by gradual loss of cerebellar neurons leading to an increasing disturbance of the balance between inhibitory and excitatory circuits in the motor system.

Central motor conduction to lower limb after transcranial magnetic stimulation in spinocerebellar ataxia type 2 (SCA2)

OBJECTIVES

To evaluate central motor conduction to lower limbs in spinocerebellar ataxia type 2 (SCA2).

METHODS

Transcranial magnetic stimulation was performed to study the corticospinal tracts of 18 patients with SCA2.

RESULTS

Central motor conduction time (CMCT) to lower limbs and thresholds were abnormal in 8 patients (44%); CMCT and thresholds were significantly correlated with disease duration and disability.

CONCLUSIONS

Corticospinal tract involvement is more frequent than previously reported in SCA2. Prolonged CMCT and increased threshold should not be used to differentiate between various type of autosomal dominant cerebellar ataxia. Similar to that reported in Friedreich's ataxia, we suggest that examining central motor conduction to the lower limbs may assist in evaluating the progressive steps of neurodegeneration in SCA2.

Prolonged postexcitatory inhibition after transcranial magnetic stimulation of the motor cortex in patients with cerebellar ataxia

Postexcitatory inhibition after transcranial magnetic stimulation of the motor cortex (silent period, SP) is supposed to be predominantly mediated by the activation of inhibitory cortical interneurons. Cortical excitability seems to be reduced in patients with cerebellar ataxia. Motor threshold, central motor conduction time and the duration of the silent period after a single magnetic stimulus to the motor cortex on both sides were measured in five patients with cerebellar ataxia of different origin and 18 healthy controls. Duration of SP was highly significantly prolonged in patients compared with controls (P<0.001) while motor threshold and central motor conduction times were not different. Fifteen of 18 control subjects showed late EMG responses after magnetic stimulation but none of the patients did (P<0.001). These findings support the hypothesis that cerebellar lesions activate inhibitory cortical interneurons or cause a disruption of a normally tonic cerebellar excitation to the motor cortex. Silent period measurement appears to be a sensitive diagnostic tool in the neurophysiological examination of cerebellar diseases.

Clinical features and genetic analysis of a Spanish family with spinocerebellar ataxia 6

OBJECTIVE

To present the clinical features and DNA analysis of a Spanish SCA6 family.

MATERIAL AND METHODS

Four symptomatic members of the family (mean age at onset: 53.75+/-5.21) were examined. SCA6 CAG trinucleotide repeat was analysed in the proband by the polymerase chain reaction (PCR).

RESULTS

Early dysphagia, ophthalmoparesis and neck dystonia in the oldest patient, without the loss of vibratory and proprioceptive sensation supporting the theory of phenotypic variability within families with SCA6. Our results are in accordance with the theory that the size of the repeat pattern correlates with the age at onset of the symptoms. Analysis of the SCA6 CAG trinucleotide repeat at the CACNA1A gene in the patient's DNA demonstrated an expanded allele of 22 CAG repeat units.

CONCLUSIONS

This study identifies phenotypic differences in the surviving kindred. The diagnosis of SCA6 in family members or single affected patients can be made by direct molecular analysis. This makes predictive testing possible.

Central motor conduction time by magnetic stimulation of the cortex and peripheral nerve conduction follow-up studies in Friedreich's ataxia

A follow-up clinical study, peripheral motor and sensory nerve conduction velocities and central motor conduction by magnetic stimulation of the cortex were performed in 13 patients with classical Friedreich's ataxia (FA) phenotype, for a period of 9-12 years. Clinical worsening was unrelated to peripheral nerve abnormalities. The amplitude of the nerve action potentials and delayed conduction velocity remained unchanged for several years. Central motor conduction times were abnormal in all patients. Clinical conditions worsened significantly between successive examinations with significant increments in threshold and significant decrement of the amplitude of motor evoked potentials. The results are consistent with progressive pyramidal and cerebellar pathways involvement as the cause of clinical worsening in FA.