**2. Multiple sclerosis**

Multiple sclerosis (MS) is the most popular autoimmune disorder of the CNS. Its prevalence may range from 2 to 100 per 100,000 in different areas of the world [1] but its incidence is absolutely rising [2]. The disease could involve any part of the CNS, leading to its wide range of manifestations. The course may be relapsingremitting or progressive. The disability is estimated via measures like the expanded disability status scale (EDSS) or patient-determined disease steps (PDDS) [3].

Acute or chronic demyelinating lesions in related cortical areas, sensorimotor pathways, and balance systems could lead to various difficulties in swallowing. Kapitza et al. also have discussed the potential role of esophageal glial cells [4]. The first reports of these symptoms go back to 1877 but it still is underestimated [5]. Dysphagia to liquids seems to be as prevalent as solid food swallowing difficulty in MS [6]. This could significantly impact the patients' quality of life [7], putting them in danger of malnutrition [8], even fatal aspiration pneumonia. The latter is the leading cause of death in MS [9]. Silent aspiration is also common (40%) [10].

#### **2.1 Epidemiology**

Dysphagia is notably prevalent among these patients. It seems to affect at least over 30% of the MS population [5]. Besides, objective examinations may find the problem in as high as 80% of the cases [5, 11]. It highlights the issue of underreporting this symptom and the importance of detailed clinical evaluation and using more advanced diagnostic tools, especially in high-risk cases [12].

On the other hand, there is a considerable discrepancy between reports from different regions. Based on a systematic review in 2015, Iran has the lowest and Europe has the highest reported prevalence of dysphagia in MS [5].

#### *Dysphagia in Neuroinflammatory Diseases of the Central Nervous System DOI: http://dx.doi.org/10.5772/intechopen.101794*

As predicted, those with higher disability scores and longer duration of disease are at more risk of experiencing deglutition difficulties [5, 11, 13, 14].

Nonetheless, it is not rare in earlier stages of the disease [14]. It could be mild and intermittent or severe and disabling. In a study from Brazil, of 108 MS patients, 90% showed different stages of dysphagia. Most cases showed mild to moderate degrees of difficulty. About 12.5% had severe dysphagia, most of whom were in progressive stages of MS and had higher EDSS [11].

#### **2.2 Pathophysiology**

Brainstem and cerebellar lesions appear to be more associated with dysphagia [13, 15]. Pharyngeal phase is more likely to be involved [13]. This could be the consequence of impaired gag reflex or uncoordinated muscle contractions [12].

To name some other pathologies that interfere with successful swallowing, we could mention cranial neuralgias and facial paresis. Cranial (trigeminal, glossopharyngeal, or occipital) neuralgias could happen in MS. These painful electricshock like attacks could alter easy swallowing in different phases, dependent on the involved area. Disturbed sensation may further complicate the process. Facial paresis could be another intervening problem. It may result in inadequate chewing that would make the bolus hard to swallow. In addition, cognitive impairment could exaggerate the problem.

### **2.3 Screening with questionnaires**

DYMUS (DYsphagia in MUltiple Sclerosis) was developed to screen MS patients for self-reported dysphagia in 2008 [16]. It is a self-assessment tool with 10 yes or no questions. Several studies evaluated the original and translated versions [17–20]. The modified version was introduced in 2020. It has shown to improve the psychometric properties of DYMUS [21]. Other less specific-to-MS questionnaires include the Eating Assessment Tool (EAT), the Swallowing Quality of Life (SWAL-QoL). EAT consists of 10 questions that provide information about functional, physical, and emotional consequences of dysphagia. It is not a time-consuming test, while 44 questions of SWAL-QoL may be considered as an important limitation. The Yale Swallow Protocol, the Gugging Swallowing Screen, and the Test of Masticating and Swallowing Solids have also been used [12]. As mentioned before, relying only on the self-reported symptoms could underestimate the problem so more in-depth clinical and paraclinical assessments may be essential. Still, patient-reported assessments may give a better picture of the psychosocial burden of the problem [16].

#### **2.4 Clinical assessment**

Paying attention to the drugs that may cause oral side effects including dysphagia should be in mind. Glatiramer acetate is a disease-modifying drug that could cause dysphagia. Anticonvulsants like clonazepam are reported to have this adverse effect. Oxybutynin, a commonly used treatment for bladder symptoms of MS, is another accusable medication. Amantadine as a fatigue treatment and dantrolene as a spasmolytic agent could also alter deglutition [17].

Apart from the standard neurological examination (mental state, cranial nerves, motor forces, sensory system, reflexes, coordination, and gait), some clues could be of help, especially for detecting unreported aspiration. For instance, dysarthria could be an indicator of concomitant dysphagia [18]. Another indicator could be coughing or choking during meal [14]. Three-ounce (90 cc) water swallowing test, although not yet validated in MS, is a sensitive tool to identify

those at risk of aspiration [19]. Some authorities recommend regular evaluations by otolaryngologists in high-risk patients [20].

Electrophysiologic methods could detect subclinical dysphagia [21, 22]. Fiberoptic endoscopic evaluation of swallowing (FEES) [23] and videofluoroscopic study of swallowing (VFSS) also seem reliable techniques [22]. FEES is a flexible endoscope introduced in 1988. It is inserted through the nose and investigates laryngeal and pharyngeal functions [24]. Grading scores show the severity of dysphagia. Some recommended this method as a standard screening method in older patients with advanced stages of MS [23]. VFSS assesses the oral, pharyngeal, laryngeal, and upper esophageal phases after ingestion of barium-containing material, in a seated position. In a study by Wiesner et al., of eight patients without any subjective complaint, only two had normal VFSS [25]. MS could result in delayed pharyngeal phase, shorter laryngeal excursion, and longer intervals between airway closure and upper esophageal sphincter opening [26].

The diagnostic steps are summarized in **Table 2**.
