**Abstract**

Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disorder of unknown etiology that affects upper and lower motor neurons resulting in progressive atrophy of skeletal muscles. There are two forms of ALS: spinal motor neuron injury and bulbar paresis. Dysphagia is a highly prevalent severe and invalidating symptom in ALS: almost 80% of ALS patients with bulbar paresis will develop dysphagia. Also, dysphagia is one of the most common and serious complications, with respiratory insufficiency, in patients with ALS as it exposes them to malnutrition, dehydration and aspiration pneumonia. These conditions are reported to be associated with a minor survival in patients with ALS. Screening for dysphagia must be performed in all ALS patients at diagnosis and during the follow-up to approach dysphagia as soon as possible. This chapter includes the latest developments in the assessment and approach of dysphagia in ALS patients.

**Keywords:** dysphagia, neurodegenerative disorder, amyotrophic lateral sclerosis, malnutrition, swallowing

### **1. Introduction**

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease that characteristically affects the upper motor neuron (located in the motor cortex) and the lower motor neuron (located in the brainstem and medullary anterior horn). As a consequence, muscular weakness ensues, which progresses to paralysis, spreading from one body region to another in a way that affects motor autonomy, oral communication, swallowing and breathing [1]. ALS is an irreversible, disabling chronic disease with serious complications.

ALS is the third neurodegenerative disease in incidence, after dementia and Parkinson's disease. It is, together with its variants, primary lateral sclerosis, progressive muscular atrophy, and progressive bulbar palsy, the most common motor neuron disease in adults. The incidence of ALS is between 1.5 and 2.5 new cases per 100,000 inhabitants per year, and the prevalence is between 4 and 6 people per 100,000 inhabitants, being relatively uniform in Western countries [2, 3].

The diagnosis of ALS is currently based on the Awaji criteria [4], respectively, the revised El-Escorial criteria [5]. Also, the Gold-Coast criteria have recently been proposed [6].

ALS occurs in two main forms: the central or bulbar form, also known as progressive bulbar palsy, and the peripheral or spinal form. In bulbar ALS, at least 80% of patients will develop dysarthria and dysphagia [7], while in the spinal or peripheral form, muscle weakness predominates, although dysphagia may appear in the evolutionary course.

Currently, there is no curative treatment, but there are some effective measures to prolong patient survival, such as nutritional management, whose aim is the prevention of malnutrition and the improvement of quality of life. Riluzole is the only medication approved for treatment of ALS by the United States Food and Drug Administration and the European Medicine Agency. Its mechanism of action is complex and includes inhibition of glutamate release, blocking of receptors for excitatory amino acids, inactivation of voltage-gated sodium channels, and stimulation of a G-protein-dependent signal transduction. Riluzole is generally well tolerated and may prolong survival by 2–3 months [8]. Recent reports suggest that riluzole could increase the survival of patients with ALS for up to 19 months [9].

Nonetheless, survival of ALS patients from diagnosis is 20% at five years after diagnosis of the disease [10]: mean survival of ALS is 3–5 years, with 5–10% living longer than 10 years [11]. The main causes of mortality are respiratory failure and malnutrition with dehydration [12, 13].

ALS patients frequently present malnutrition, this being an independent prognostic factor for survival [14]. The causes of malnutrition are the appearance of dysphagia, whose prevalence reaches 80% in the evolutionary course of ALS, as well as the decrease in intake due to loss of autonomy, muscle atrophy, fatigue and increased energy requirements.

The prevalence of malnutrition varies from 16 to 53% depending on the parameters used [15], the form of presentation of the disease and the moment in its evolutionary course. Therefore, a nutritional assessment is recommended in all patients diagnosed with ALS, whether bulbar or spinal, at the time of diagnosis of the disease [12].

The follow-up and nutritional approach of these patients is chronic, without considering the possibility of discharge or end of follow-up. However, there are no precise premises regarding follow-up (frequency of visits) [12]. Furthermore, it is important to bear in mind that the management of these patients is multidisciplinary (Pneumology, Neurology, Rehabilitation, etc.) and requires closer surveillance than other types of patients.

Swallowing is a complex act that relies on the correct coordination of motor and sensory systems of oral, pharyngeal and esophageal strictures. Dysphagia is defined as the difficulty in passing the food bolus from the mouth to the stomach caused by the anatomical or functional alteration of various structures involved in swallowing. It includes the behavioral, sensory and motor alterations that occur during swallowing, including the state of consciousness prior to the act of eating, the visual recognition of food and the physiological responses to the smell and presence of food.

Swallowing disorders can appear acutely or insidiously and progressively. Dysphagia is classified according to its etiology (mechanical or motor) or according to its location (oropharyngeal or esophageal).

In ALS patients, dysphagia is progressive, motor, and occurs both at the oropharyngeal and esophageal levels. Its prevalence is 30% at diagnosis, with an increasing incidence as the disease evolves, appearing in up to 80% of patients with ALS [7, 12].

The importance in the diagnosis of dysphagia lies in its complications, derived from a decrease in a reduction in the efficacy and safety of swallowing. Complications from dysphagia include malnutrition, dehydration, aspiration and pneumonia. Malnutrition and aspiration increase the risk of death by 7.7 times in ALS patients, hence the importance of its diagnosis and approach [11].
