Muscular Dystrophy

DMD is an X-linked disease affecting 1 in 3600 to 1 in 6000 live male births. Mutations of the dystrophin gene (Xp21.2) result in progressive muscle degeneration and replacement with interstitial fat and fibrosis. Diagnosis at presentation is typically around age 5 years and precipitated by divergent physical ability compared with peers. Children commonly have progressive muscle weakness resulting in loss of ambulation. In late stages, cardiopulmonary sequelae result in life-threatening complications and, in the absence of intervention, the mean age of death is 19 years.

Dysphagia in DMD is most symptomatic in the late nonambulatory phase of disease. Aloysius and colleagues evaluated the role of videofluoroscopy in children with DMD and feeding difficulties. Oral phase difficulties predominated and resulted from masticatory muscle weakness, malocclusion, and macroglossia. The swallow trigger was mildly delayed and weak pharyngeal propulsion resulted in pharyngeal residue. Patients were also desensitized to residue. Choking episodes occurred with more advanced disease, although no patients showed aspiration on videofluoroscopy. van den Engel-Hoek and colleagues examined dystrophic changes in the oral muscles of swallow in patients with DMD. They found that increased echogenicity in digastric muscles, geniohyoid, and superior longitudinal muscles was associated with reduction in strength and a need for multiple swallows to clear the oral cavity. Weakened anterosuperior excursion of the hyoid results in a reduction of laryngeal protection and delayed opening of the upper esophageal sphincter. Early recognition of these findings facilitates a greater role for supportive care during these advanced stages.

Myasthenia Gravis

MG is an autoimmune postsynaptic neuromuscular junction disorder. It predominantly affects women in the third and fourth decades, although male patients show a bimodal peak in the third and sixth decades. Anti–acetylcholine receptor antibodies reduce the available number of acetylcholine receptors and result in subthreshold endplate potentials. The clinical features involve painless weakness of striated muscle. Although ocular manifestations are the most common, bulbar weakness may be the presenting symptom in up to 6% to 15%. Patients may also present with dysphonia characterized by vocal weakness and fatigue, and may even have vocal fold paresis with consequent increased aspiration to liquids. Natural history of the disease is progression to maximum severity within 2 years.

Colton-Hudson and colleagues found that the oral preparatory phase was affected with poor bolus formation, extended chewing, and reduced buccal tension. Oral phase abnormalities included slow transit, piecemeal deglutition, increased residue, and poor seal. The most common findings were in the pharyngeal phase, and included delays in initiation and a reduction in tongue base and epiglottic mobility. Weak constrictor muscles result in pharyngeal residue. Laryngeal penetration was common (35%) and often silent. EMG studies reveal prolongation of suprahyoid laryngeal elevators in MG, which may compensate in those with subclinical swallow impairment. In this disorder, cricopharyngeal muscle function is usually normal. Proper diagnosis is critical to management of the disease, and aggressive medical therapy should result in dramatic improvement of dysphagia.

Multiple Sclerosis

MS is a central, demyelinating, immune-mediated disease with a female predominance. Incidence is 2 in 100,000 to 7 in 100,000 and peaks at around 30 years. MS is triggered by environmental factors in genetically at-risk patients, and a focal lymphocytic infiltrate results in myelin and axonal damage. Median time to death is approximately 30 years from disease onset.

The incidence of dysphagia varies depending on the severity of the disability from 24% to 65%, and is most severe in those with brainstem involvement. Aspiration pneumonia is consequently the leading cause of death in MS. Abnormalities include reduced lingual control and tongue base retraction, delayed swallow trigger, reduced laryngeal closure and pharyngeal contraction, and diminished sensation. The oral phase is more often affected in those with severe dysphagia. Oromotor impairment also results in the characteristic dysphonia with scanning speech. Upper esophageal sphincter dysfunction is common and most pronounced with disease progression, with reduced compliance rather than deficient traction as the postulated mechanism. As a result, coughing and choking episodes were reported in most patients with dysphagia. In addition to these aspects of dysphagia, patients with MS have impaired motor control of their limbs and hands resulting in compromised ability to feed themselves.

Amyotrophic Lateral Sclerosis

ALS (also known as motor neuron disease) is an idiopathic neurodegenerative disorder. Its incidence is approximately 2 in 100,000 and it affects men more than women. Peak onset of sporadic disease (approximately 90%–95% of cases) occurs at 58 to 63 years, with familial disease approximately 1 decade earlier. Familial disease has mendelian inheritance. Pathophysiology involves degeneration and loss of motor neurons with astrocytic gliosis.

The hallmark clinical feature is the presence of upper and lower motor neuron features involving the brainstem and spinal cord. Fifty percent of patients die within 30 months of symptom onset, but the prognosis is better in those with isolated bulbar disease. Presentation with limb-onset disease predominates (70%), but bulbar onset occurs in approximately 25%. The tongue is disproportionately affected compared with other musculature and therefore oral preparatory and oral phase are most affected. Upper motor neuron dysfunction results in a brisk gag and jaw jerk, whilst lower motor neuron involvement causes tongue fasciculation, wasting and weakness, palatal weakness, and poor cough.

Ertekin and colleagues investigated the pathophysiologic mechanisms of dysphagia in ALS. They concluded that the swallow trigger reflex was delayed, disordered, and eventually absent, but that reflexive swallow was preserved until the end-stage disease. The cricopharyngeus muscle became hyper-reflexive and hypertonic, with a resultant loss of coordination during voluntary swallow initiation and laryngeal protection. Aspiration risk is high, and there are premier roles for supportive care and family support.

Parkinson’s Disease

PD is a common progressive bradykinetic disorder with an incidence of approximately 13 in 100,000 and a 1.5% lifetime risk of development. Median age of onset is 60 years and mean duration of disease is 15 years, with aspiration pneumonia the most common cause of death. The disease is characterized by bradykinesia, and one of muscular rigidity, a 4-Hz– to 6-Hz resting tremor, or postural instability. The underlying pathophysiology is severe loss of dopaminergic neurons in the pars compacta nigral cells of the basal ganglia. However, atypical PD and Parkinson plus syndromes such as progressive supranuclear palsy are increasingly recognized. The prototypical parkinsonian voice is weak, soft, and hypokinetic.

EMG and esophageal scintigraphy studies reveal that there is a high rate of objective dysphagia, even in asymptomatic patients, and objective pooled prevalence rates of dysphagia are 82%. Potulska and colleagues noted prolongation of lower esophageal bolus transport in all patients. The oral preparatory and oral phases became affected later in the disease, reflecting the progression of tremor, bradykinesia, and rigidity. The dorsal motor nucleus of vagus and esophageal myenteric plexus degenerate, and this results in both pharyngeal and esophageal phase dysphagia.

Although there are increasing options for the treatment of PD medically and surgically with brainstem electrical stimulation, there are hallmark on-off effects of medication that limit seamless management of dysphagia. For example, timing of traditional medication results in a peak of agility followed by a decline in function until the next dose is used, so swallowing is safer during the period of agility rather than when the medication is wearing off. Fatigue is also a common problem with patients with PD, and similarly affects aspiration risk during the part of the day when present.