**2. Clinical features of cerebellar dysfunction in MS**

Cerebellar dysfunction is a typical feature of MS, which results in a wide range of neurological manifestations. The clinical signs of cerebellar involvement in MS include gait ataxia, dysmetria when performing the finger-to-nose and heel-to-shin tests, and the inability to perform tandem gait [4]. Cerebellar involvement in MS results from both vermian and hemispheric lesions. Up to 50% of MS patients may experience intention tremor and limb ataxia [4]. Indeed, MS frequently causes coordination issues, which are mostly brought on by pathology in the cerebellum itself or dysfunction in cerebellar connections, including proprioceptive afferent inputs. Depending on the exact location of the lesion, cerebellar dysfunction can cause limb, gait, and truncal ataxia as well as other cerebellar characteristics including dysarthria, and tremor [13]. MS patients exhibit signs of either chronic cerebellar abnormalities in a progressing disease or acute cerebellar impairment related to an acute relapse [13]. A higher incidence of cerebellar involvement during successive relapses appears to be linked to cerebellar relapse in the early stages of the disease [14].

It is believed that injury to the anterior lobe of the cerebellum is the primary cause of gait ataxia [15]. Cerebellar dysarthria is a rare symptom at disease initiation but is common in people with secondary progressive diseases that have worsened [13]. Although paroxysmal MS symptoms are rare, paroxysmal dysarthria with ataxia has been documented in MS and is thought to be related to midbrain pathology [16, 17]. Sensory evaluation (sensory ataxia) based on as scoring from 0 to 4, shows minimal sensory impairment in MS patients. The minimal sensory impairment detected clinically was found to be more prominent in the electrophysiological studies [7].

A recent database research of over 15,000 patients found that there were nearly 50,000 total relapses. Cerebellar relapses made up about 10% of those, and they were more common in men and in people who had had the disease for a longer period of time [18]. Poor relapse recovery is also linked to cerebellar/brainstem relapses, which are linked to an earlier onset of progressive disease [13].

Likewise, tremor is a common symptom of MS and has been found in more than half of MS patients who visit specialized clinics [11]. Clinical studies have revealed that tremor was clinically detected in 18 MS patients and absent in 14 patients. While

### *Ataxia in Multiple Sclerosis: From Current Understanding to Therapy DOI: http://dx.doi.org/10.5772/intechopen.112013*

MS patients who had a visible tremor had an ataxia score that was more severe and showed clinical symptoms of cerebellar dysfunction [19]. It is worth mentioning that cerebellar ataxia is generally associated with tremor, which typically happens during voluntary movements or while maintaining a position [11]. MS tremor is believed to be mostly brought on by cerebellar and/or thalamic dysfunction [20]. Otherwise, tremor can occur in the head, limbs, vocal cords, and trunk. Though rest and rubral tremors are uncommon, intention and postural tremors are the most prevalent types [21, 22]. Whereas, severe tremor, which is thought to affect 3% of MS patients, is a very uncommon but severely debilitating MS complication [22]. The pathophysiology of tremor in MS is complex and is thought to involve connections between the cerebellum, cerebral cortex, and basal ganglia [13]. Given the significance of cerebellar connections in motor control, it may not be surprising that the involvement of the cerebellum is associated with higher impairment and a worse prognosis.
