Multiple Sclerosis is an inflammatory demyelinating disorder affecting the Central Nervous System (Wilkins, 2017). It is characterized by its heterogeneous clinical presentations and the variable disease severity depending on the affected region of the Central Nervous System (CNS) (Wilkins, 2017). About one-third of Multiple Sclerosis (MS) patients, worldwide, suffer from affection of the cerebellum and/or any segment of the cerebellar loop either during the acute disease relapse or during the process of chronic disease progression (Parmar et al., 2018). More than 40 % of patients with MS, in Egypt, developed Ataxia during the disease course, according to the Egyptian Registry (Hamdy et al., 2017).

The cerebellar loop allows the cerebellum, along with the multiple cerebral areas, to exert its motor and cognitive functions (D'Mello et al., 2020). It consists of an afferent Cortico-Ponto-Cerebellar (CPC) pathway that transmits information from different cortical areas to the cerebellum (Palesi et al., 2017). The efferent fibres transmit the information from the cerebellum back to the cerebral cortex via the Cerebello-Thalamo-Cortical (CTC) system (Palesi et al., 2017). Disruption of the integrity of this loop results in incoordination, which presents clinically in the form of ataxia, nystagmus, tremors, and dysarthria (Billeri and Naro, 2021). These symptoms have a significant contribution to reducing patients' mobility, increasing disability, and hence, significant impairment in the patients’ quality of lives (Kenyon et al., 2022). Despite the presence of various strategies for the treatment of ataxia, such as medical treatment, physiotherapy, and stereotactic surgical intervention, limited effectiveness is still troublesome (Stephen et al., 2019).

Repetitive Transcranial Magnetic Stimulation (rTMS) is an evolving non-invasive, outpatient procedure that works through cortical excitability modulation using a magnetic field (Lefaucheur et al., 2020). The magnetic field from the stimulators induces an electrical current that results in the depolarization of neurons transiently during the session. However, long-term cellular and molecular mechanisms are activated, resulting in modulation of function (Goldsworthy et al., 2021).

The effect of the rTMS depends on multiple several protocol related parameters, including the cortical target, the protocol used during the sessions (adjusting intensity and frequency of stimulation), the number and the duration of the sessions. Moreover, there are some patient factors that also affects the response to the rTMS such as the patient age, the type, severity, and the primary aetiology of the symptoms (Lefaucheur et al., 2020). rTMS has been proven to be effective in many neurological diseases as Tourette's Disorder, post-stroke cerebellar dysfunction, Spasticity, Parkinson's Disease, functional tremors, and cortical myoclonus (Adeloye et al., 2020).

The rTMS frequently causes mild to moderate adverse effects that disappear quickly after the session. More sessions result in a progressive decrease in such side effects. Possible side effects include headache, tingling, light-headedness, facial muscle twitches or spasms, and tenderness in the scalp (Lefaucheur et al., 2020).

The aim of the current study is to assess the therapeutic response of high-frequency rTMS as a treatment modality of truncal ataxia in Relapsing-Remitting Multiple Sclerosis (RRMS) patients on both the functional and the microstructural levels using patients’ clinical assessment and Diffusion Tensor Imaging (DTI) assessment of the Fractional Anisotropy (FA) of the CPC and the CTC pathways respectively.