NEUROLOGY & PHYSIOLOGY OF BILATERAL STROKE DYSPHAGIA
The following section gives information about the neurology and physiology of bilateral stroke dysphagia. Specific emphasis is placed on age-related changes, cortical re-organisation, lesion localisation, the proposed neural pathway of the swallow and 'typical' symptoms of this population.

Age-related Changes
Sourced from: http://www.melrosegardens.com/images/teasm.jpg
Sourced from: http://www.melrosegardens.com/images/teasm.jpg


An understanding of the normal swallow is paramount when considering dysphagia caused by stroke, for information about the four stages of the normal swallow click here. Because stroke is more common in the elderly, and bilateral stroke even more so, not only is the normal swallow of importance but also the normal aging process of the swallow. Age related changes are important because coupled with bilateral stroke dysphagia they further compound the severity of bilateral stroke dysphagia (Martino, Foley, Bhogal, Diamant, Speechley & Teasell, 2005). Post stroke elderly patients may no longer be able to compensate for these normal changes, resulting in a combination of dysphagia due to stroke and age related changes. For a list of important age related changes that may intensify dysphagia symptoms click here.
For information about the muscles and cranial nerves involved at each stage of the swallow click here.


Cortical Re-organisation

Another aspect that contributes to the severity of dysphagia in this population is the inability for compensatory re-organisation to occur. Research has shown that due to the asymmetry of the swallow within the two hemispheres, the undamaged hemisphere is, over time able to re-map the swallowing functions of the damaged hemisphere (Hamdy & Rothwell, 1998). Due to the bilateral nature of stroke in this population re-organisation is unable to occur. This has a significant effect on the future management of bilateral stroke dysphagia patients, not only can they be expected to have more severe dysphagia but therapy will most likely be intensive and be long lasting (Hamdy & Rothwell, 1998).

The Neural Pathway

The neural pathway for deglutition has not been fully determined. The research states swallowing is a distributed neural network that runs through both hemispheres and into the medulla, which has been located as the swallowing centre (Daniels & Foundas, 1999). Specific locations and pathways have been proposed but a direct neural pathway and specific localisations and functions have not yet been proven. The diagram below outlines the proven and hypothesised pathway of the swallow:




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Sourced from Daniels and Foundas (1999)


Localisation of Dysphagia
It is not surprising that due to the lack of knowledge about the neural pathway of the swallow that the findings about localisation of lesion and associated dysphagia are also inconsistent and controversial. Due to the location of hemispheric stroke in this population brainstem localisation will not be discussed. Some studies state that the place of lesion does not affect the area of impairment, while other studies found that distinct acute brain lesion locations do result in characteristic swallowing disturbance patterns (Cherney, 1994). For the purpose of this website, due to the variability of the literature a stance of no lesion to impairment correlation is taken. This view is based on the research of Daniels & Foundas (1999), Lieberman & Sievers (1992) and Alberts, Horner, Gray & Brazer (1992). These studies (among many others) state that difficulty in the different stages of the swallow and the risk of aspiration are not correlated with a specific hemisphere or location of stroke. Daniels and Foundas (1999) do however state that anterior lesions are more common than posterior lesions in people with dysphagia, and that lesions in the prevantricular white matter and pre-motor cortex are likely to be associated with specific dysphagia symptoms. They assert that extensive research in the localisation of dysphagia alongside a better understanding of the neural pathway of the swallow is likely to uncover correlations between the two. Maurizo (2004) states that size of lesion is a better predictor of the risk of dysphagia than localisation of stroke. Due to the conflicting nature of the research it is important that each patient’s symptoms be considered as unique so their specific swallowing difficulties can be identified.

Dysphagia after Stroke

The above inconsistencies combined with a lack of research on bilateral lesions mean that the symptoms of dysphagia in the bilateral hemispheric stroke population are extremely variable. Thus, research pertaining to hemispheric stroke in general will be used to identify common dysphagia symptoms for this population. A variety of swallowing deficits have been associated with hemispheric stroke, the following list is sourced from Groher and Crary (2010):
  • Poor initiation of saliva swallows (dry swallow).
  • Delay in initiation of pharyngeal component of swallow.
  • Inco-ordination of oral components of mastication (cause by muscle weakness / paralysis of face and tongue).
  • Inco-ordination, weakness and paralysis of muscles needed to sit up to eat and bring food towards mouth.
  • Increased pharyngeal transit time
  • Reduced pharyngeal constrictor and clearing.
  • Aspiration (solids in particular).
  • Dysfunction of the cricopharyngeal muscle.
  • Poor relaxation of lower oesophageal sphincter.

Groher and Crary (2010) indicate that dysphagia following stroke is not limited to any specific stage of swallow and that stroke can impair swallowing functions from mouth to stomach.

It must also be noted that in the acute stage of stroke pre-oral anticipatory aspects of deglutition are very significant. At this stage the patient is in hospital, and is not in control of preparing or feeding themselves (due to the acute nature and co-morbid conditions surrounding bilateral stroke). This is important because it has been noted that dysphagia can be significantly worse when a patient is not feeding themselves. Groher & Crary (2010) note that during fluoroscopic swallow significant improvements in swallow were seen if the patient was given the opportunity to feed themselves (with the help of carers).