Are the neurophysiological techniques useful for the diagnosis of diaphragmatic impairment in multiple sclerosis (MS)?

Novel role for non-invasive neuromodulation techniques in central respiratory dysfunction

Respiration is a crucial steady-state function of human life. Central nervous system injury can damage the central respiratory pattern generator (CRPG) or interrupt its outflow, leading to central respiratory paralysis and dysfunction, which can endanger the patient's life. At present, there is no effective means to reverse this process. Commonly used non-invasive neuromodulation techniques include repetitive transcranial magnetic stimulation (rTMS), transcranial direct current stimulation (tDCS) and so forth, which have been widely applied in nervous system diseases and their various secondary symptoms, but rarely in respiratory function. Clinical and animal studies have confirmed that TMS is also suitable for investigating the excitability and plasticity of ascending corticospinal respiratory pathways. In addition, although rTMS and tDCS differ in their respective mechanisms, both can regulate respiratory networks in healthy individuals and in diseased states. In this review, we provide an overview of the physiology of respiration, the use of TMS to assess the excitability of corticophrenic pathways in healthy individuals and in central respiratory disorders, followed by an overview of the animal and clinical studies of rTMS, tDCS and so forth in regulating respiratory circuits and the possible mechanisms behind them. It was found that the supplementary motor area (SMA) and the phrenic motor neuron (PMN) may be key regulatory areas. Finally, the challenges and future research directions of neuroregulation in respiratory function are proposed. Through understanding how neuromodulation affects the respiratory neural circuit non-invasively, we can further explore the therapeutic potential of this neuromodulation strategy, so as to promote the recovery of respiratory function after central nervous system diseases or injury.

Clinical diagnostic utility of transcranial magnetic stimulation in neurological disorders. Updated report of an IFCN committee

The review provides a comprehensive update (previous report: Chen R, Cros D, Curra A, Di Lazzaro V, Lefaucheur JP, Magistris MR, et al. The clinical diagnostic utility of transcranial magnetic stimulation: report of an IFCN committee. Clin Neurophysiol 2008;119(3):504-32) on clinical diagnostic utility of transcranial magnetic stimulation (TMS) in neurological diseases. Most TMS measures rely on stimulation of motor cortex and recording of motor evoked potentials. Paired-pulse TMS techniques, incorporating conventional amplitude-based and threshold tracking, have established clinical utility in neurodegenerative, movement, episodic (epilepsy, migraines), chronic pain and functional diseases. Cortical hyperexcitability has emerged as a diagnostic aid in amyotrophic lateral sclerosis. Single-pulse TMS measures are of utility in stroke, and myelopathy even in the absence of radiological changes. Short-latency afferent inhibition, related to central cholinergic transmission, is reduced in Alzheimer's disease. The triple stimulation technique (TST) may enhance diagnostic utility of conventional TMS measures to detect upper motor neuron involvement. The recording of motor evoked potentials can be used to perform functional mapping of the motor cortex or in preoperative assessment of eloquent brain regions before surgical resection of brain tumors. TMS exhibits utility in assessing lumbosacral/cervical nerve root function, especially in demyelinating neuropathies, and may be of utility in localizing the site of facial nerve palsies. TMS measures also have high sensitivity in detecting subclinical corticospinal lesions in multiple sclerosis. Abnormalities in central motor conduction time or TST correlate with motor impairment and disability in MS. Cerebellar stimulation may detect lesions in the cerebellum or cerebello-dentato-thalamo-motor cortical pathways. Combining TMS with electroencephalography, provides a novel method to measure parameters altered in neurological disorders, including cortical excitability, effective connectivity, and response complexity.

A Narrative Review of Respiratory Impairment, Assessment, and Rehabilitation in Multiple Sclerosis

<b><i>Background:</i></b> Respiratory impairment is a problem seen in people with multiple sclerosis (pwMS) from the early stages of the disease but not frequently recognized by clinicians until the later stages. It is seen in different ways, such as respiratory muscle weakness, change in pulmonary volumes, and decrease in cough efficiency. This situation has consequences affecting individuals’ physical fitness, participation in daily life, and quality of life. <b><i>Summary:</i></b> This review explains possible respiratory impairment mechanisms, related problems, assessment, and rehabilitation approaches in pwMS. <b><i>Key Messages:</i></b> It is recommended a comprehensive assessment of respiratory functions in pwMS regardless of the disease severity and stage. In addition, pulmonary rehabilitation and other exercises can have positive effects on the respiratory functions of pwMS. In future studies, specific training parameters should be determined for pwMS to achieve optimal benefits. There is also a need for studies that apply respiratory muscle training in pwMS who have a high disease severity and limited participation in the activities of daily living.

Evolving relationship between respiratory functions & impairment in sleep and cognition in patients with multiple sclerosis

BACKGROUND

The most apparent source of disability in patients with multiple sclerosis (MS) is the physical and mental impact. The pathophysiological mechanisms of cognitive dysfunction are multifactorial although hypoventilation secondary to respiratory dysfunction may contribute to cognitive decline.

METHODS

This study was conducted on 146 MS patients with baseline clinical assessments including the Epworth sleepiness scale (ESS) and physical disability was assessed using the Expanded Disability Status Scale (EDSS). Cognitive testing was performed utilizing the Brief International Cognitive Assessment for Multiple Sclerosis (BICAMS) and the Perceived Deficits Questionnaire (PDQ). Respiratory functions were assessed by spirometry and the respiratory muscle functional assessment was done by maximal mouth pressure measurement.

RESULTS

The respiratory muscle function test had a significant negative correlation with the score of ESS and PDQ scale and a significant positive correlation with the BICAMS scale score (p < 0.001). The ESS and PDQ scores were significantly negatively correlated with forced expiratory volume in the first second (FEV1)/ forced vital capacity (FVC) (p = 0.03, 0.02), FVC supine (p = 0.03, 0.01), FVC upright- FVC supine (ΔFVC) (p < 0.001, <0.001) FEV1 (p < 0.001) and FVC (L) (p < 0.001), respectively. While the BICAMS showed a significant positive correlation with spirometry results except FVC upright. ESS scores were significantly correlated with the BICAMS and PDQ scale score (p < 0.001).

CONCLUSION

Among MS patients, impaired respiratory functions are significantly associated with sleep disturbance and cognitive impairment. Thus the spirometry and respiratory muscle strength assessment are necessary from the early phase of MS.

Respiratory dysfunction in multiple sclerosis

Respiratory dysfunction frequently occurs in patients with advanced multiple sclerosis (MS), and may manifest as acute or chronic respiratory failure, disordered control of breathing, respiratory muscle weakness, sleep disordered breathing, or neurogenic pulmonary edema. The underlying pathophysiology is related to demyelinating plaques involving the brain stem or spinal cord. Respiratory complications such as aspiration, lung infections and respiratory failure are typically seen in patients with long-standing MS. Acute respiratory failure is uncommon and due to newly appearing demyelinating plaques extensively involving areas of the brain stem or spinal cord. Early recognition of MS patients at risk for respiratory complications allows for the timely implementation of care and measures to decrease disease associated morbidity and mortality.

The cortico-diaphragmatic pathway involvement in amyotrophic lateral sclerosis: neurophysiological, respiratory and clinical considerations

Cortico-diaphragmatic pathway was investigated by means of transcranial magnetic stimulation (TMS), in 14 patients affected by definite amyotrophic lateral sclerosis (ALS) without clinical signs of respiratory impairment. Spirometry, gas analysis, and measurement of static inspiratory and expiratory pressures were performed in all patients. Forced vital capacity, forced expiratory volume at the first and second peak expiratory flow, sniff effort from FRC level (SNIP), maximal inspiratory and expiratory pressure at mouth (MIP/MEP), maximal transdiaphragmatic pressure (Pdimx) were considered. TMS was performed, recording by surface electrodes from hemidiaphragm, bilaterally. Latency of cortical and spinal motor-evoked potentials (Cx-MEP/Sp-MEP) and central motor conduction time (CMCT) were measured. None of the patients showed altered spirometry and gas levels. Seven patients showed decreased Pdimx and eight of MEP values. Four patients showed a delayed Sp-MEP. In one patient the Cx-MEP was abolished while the mean values of both Cx-MEP and CMCT were significantly increased (19.2+/-4.1 ms, P<0.0001; 10.8+/-4.8 ms, P<0.0001). Cx-MEP and CMCT did not show significant correlations with any of the respiratory measures. The patients with prolonged Sp-MEP, showed longer disease duration, lower Norris score, lower Pdimx and MEP values. In conclusion, cortico-diaphragmatic study is a sensitive measure to reveal subclinical diaphragmatic impairment although not correlated to respiratory measures.