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Thesis Lenie van den Engel-Hoek: Dysphagia in children with neuromuscular disorders
20 August 2013
On 25 april 2013, Lenie van den Engel-Hoek defended her thesis "Dysphagia in children with neuromuscular disorders" at the Radboud University in Nijmegen. 

In recent years, there have been important advances in our understanding of the normal neurological regulation, physiology of feeding and swallowing and the mechanisms by which different consistencies are swallowed. In the Children’s hospital of the Radboud University Medical Centre (department Rehabilitation – Speech-Language Therapy) children are seen with feeding and swallowing disorders due to a wide range of disabilities. Based on extensive experience with many children referred to our multidisciplinary university-hospital outpatient swallowing clinic, certain swallowing characteristics of children with the same etiology were noticed. For example, children with cerebral palsy (CP) are at risk of aspiration of thin fluid. Recommendations for safe oral feeding in this patient group are traditionally focused on changing posture during feeding and thickening fluids. We hypothesized that other disturbances than in children with CP would be the cause of dysphagia in children with neuromuscular disorders.

A retrospective review of the videofluoroscopic swallow studies (VFSS) of 118 children, divided into three groups (spastic CP, dyskinetic CP, and neuromuscular disorder), referred to our university-hospital swallowing team, was performed. Different patterns of dysphagia among the groups could be distinguished with regard to swallowing phase and type of food (liquid or pureed food). Dysphagia in children with CP was characterized by loss of food out of the mouth, nasopharyngeal backflow and aspiration, especially with thin liquid. Dysphagia in children with neuromuscular disorders was characterized by more problems with thick liquid or solid food with piecemeal deglutition and pharyngeal post-swallow residue. 
Although a VFSS is the most commonly used tool in the assessment of dysphagia, it does not always provide sufficient insight in the underlying factors of swallowing problems in case of neuromuscular disorders. Hence, a study was conducted to investigate whether quantitative muscle ultrasound, using gray-scale analysis, was feasible to assess oral muscles. In a study with 53 healthy subjects, aged 5 – 30 years, it was shown that muscle thickness and echo intensity of the submental and tongue muscles can be described as Z-scores and used to quantify healthy and affected muscles. In addition, biomechanical events during swallowing can be measured using surface electromyography (sEMG) activity of the submental muscle group and anterior tongue pressure (ATP) recordings. Because no such data were available in children, 78 healthy participants from 5 to 65 years were assessed during swallowing of saliva and 5 ml volumes of water, custard and pureed potato. To describe the differences among the consistencies, we used relative changes in sEMG and ATP values, which controls for inter-individual variations, using the swallowing of water as a reference. The findings of this study can easily be used in other studies as well as in clinical settings, because the relative changes compared to water are described. 
To describe the dysphagia in children with Spinal Muscular Atrophy II (SMA II) and Duchenne Muscular Dystrophy (DMD) two studies were performed. A VFSS and measurements with sEMg and tongue pressure were performed during swallowing. In the DMD patients also  quantitative muscle ultrasound of the oral muscles was performed. It was concluded that the dysphagia in SMA II is due to neurologic dysfunction, affecting the muscle force and movement efficiency of the tongue and the submental muscle group, in combination with a compensatory retracted head posture. This compensatory head posture also influences the mandibular function, probably resulting in a limited mouth opening. These results have led to an integrated treatment advice to prevent  pneumonias, that might be the result of aspiration of pharyngeal residue. Adopting an adjusted posture during meals and drinking water after meals are essential. 
The DMD patients were divided in three groups, based on the stage of their disease: early and late ambulatory stage (AS, N=6), early non-ambulatory stage (ENAS, N=7), and late non-ambulatory stage (LNAS, N=11). In the VFSS none of the patients showed direct aspiration, but oral phase problems and pharyngeal post-swallow residue were often observed, more in the LNAS than in the AS and ENAS, most frequently with thick liquid and solid food. It was shown that in DMD oral muscles are not spared, starting in the youngest group with dystrophic change in the geniohyoid muscle. A gradual increase in echo intensity was found also in other oral muscles, influencing the sEMG and tongue pressure data of swallowing solid food. The data shows that in DMD the complex function of swallowing, with involvement of various oral and pharyngeal muscles, is changing over time. Based on the disturbed mechanisms, recommendations are given for efficient and safe swallowing in the different stages of DMD. In this study it was also found that thickness of the tongue was increased (> 2 SD) in 70% of the patients in the ENAS and LNAS. In the ENAS we found an increase in tongue thickness without increased echo intensity, which can be considered hypertrophy. In the LNAS there was an increased echo intensity in tongue muscles, indicating that muscle fibers are replaced by fat and fibrosis. We suggest that the macroglossia in the LNAS, based on the significant correlation between increased echo intensity and tongue thickness, is a pseudohypertrophic phenomenon.   
By describing the dysphagia of a 6-week-old girl with a congenital myopathy who was referred to our university-hospital with an aspiration pneumonia, it was possible to test the theory that the cortically guided coordination of swallowing was normal in this girl, but that her choking was due to post-swallow residue.   
Fact sheets have been developed for parents and children with SMA II and DMD. Although several underlying mechanisms of dysphagia in children with neuromuscular diseases were uncovered in the studies of this thesis, not all mechanisms could be addressed. Therefore, future studies should focus on other mechanisms and other neuromuscular disorders in search of disease-specific problems. For clinicians working with children and young adults with neuromuscular disorders, the underlying mechanisms of oral and pharyngeal dysphagia are important to consider to improve recommendations and protocols for efficient and safe swallowing.

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