TRANSCRANIAL MAGNETIC STIMULATION IN LARYNGEAL PARALYSIS: A SINGLE INSTITUTION EXPERIENCE

The paralysis of the vocal cords is still today a diagnostic-therapeutic challenge in the field of otolaryngology, placing doctors and voice professionals in continuous search of non-invasive therapeutic solutions to ensure patients an adequate quality of life. It can result from neurological damage or mechanical fixity of the true vocal cord. It can be monolateral or bilateral. In 96% of cases, it will be unilateral paralysis (UVFP), while only 4% will be bilateral paralysis (BVFP). The most common cause of UVFP is neoplastic lesions (35.5%). Among these, cancer that most frequently causes UVFP is lung cancer. The second cause of UVFP is represented by iatrogenic damage to the recurrent laryngeal nerve (24.6%), especially during thyroid surgery. About 13% of UVFP are related to systemic pathologies, 6% are a consequence of laryngeal trauma, and in 14% of cases, it is impossible to identify the cause of paralysis, so they are defined as idiopathic. Long-term survival data suggest that patients with idiopathic UVFP have no change in life expectancy, with a 33% chance of progressive vocal improvement over time. Most of these patients spontaneously recover laryngeal motility in less than one year, but in a small percentage of cases, a motility recovery can be observed even after one year from the onset of symptomatology. The neuromuscular system of the larynx can be damaged both at the motor level (efferent) and the sensory level (afferent). In clinical practice, motor damage results in a complete or partial loss of motility of one or both vocal cords, resulting in an apparent glottic asymmetry. Although the clinical evaluation allows an adequate evaluation of laryngeal motility, it is not always possible to accurately assess the cause and degree of motor disorders of the vocal cords with a videolaryngoscope alone. Neurophysiological methods, especially laryngeal electromyography (LEMG), can help us understand the pathological condition underlying the laryngeal motor disorder. Transcranial magnetic stimulation (TMS) has recently been proposed as a non-invasive and painless tool capable of activating the motor pathways. This technology is based on magnetic stimuli that can induce a flow of current at the tissue level and, therefore, activate the excitable structures, especially the neurons of the cerebral cortex, of the spinal cord or directly the motor axons of the peripheral nervous system. The motor pathways' activation consequently generates muscle activation, where bioelectric signals can be recorded by surface or needle electromyography. TMS is currently used for the functional study of the motor pathways, allowing, for example, to target lesions of the first neuron in encephalic diseases (e.g., multiple sclerosis, stroke, amyotrophic lateral sclerosis) and spinal cord. Used to stimulate the cerebral cortex, TMS has been shown to change neuronal excitability in the short to medium term, both excitatory and inhibitory, and to induce changes in neuronal plasticity. For example, repetitive TMS has been shown to treat the major depressive disorder. Few data exis in the literature regarding the study of the motor pathways directed to the laryngeal musculature. Then study on which this thesis is based aims to set up at our laboratory a technique to evaluate the function of the motor pathways directed to the vocal muscles with the ultimate aim of objectifying lesions of the cortical-laryngeal in patients with idiopathic paralysis of the vocal muscles.