The term dysphagia refers to difficulties with the passage of food all the way from the mouth to the stomach, but not to pain caused by swallowing (odynophagia). The previous pages mainly summarised signs and symptoms, below we look in a little more detail into causes and mechanisms of dysphagia.
Some general remarks
Dysphagia can be related to a number of different conditions, with oral & maxillofacial causes being only one aspect. There is considerable overlap between various clinical disciplines involved in the diagnosis and treatment of swallowing disorders. The clinical disciplines include oral & maxillofacial surgery, dentistry, otolaryngology (ENT; (ear, nose and throat)), neurology and neurosurgery, paediatrics, oncology, general surgery (in particular gastric and thoracic), rheumatology. Support roles in the management and rehabilitation of dysphagia include specialised nursing support, speech & language therapy, occupational therapy, physiotherapy and diet & nutritional advice.
Considering the complicated normal processes of swallowing, it is no surprise that there are many different ways in which dysphagia can occur. A successful swallowing manoeuvre requires excellent coordination at all stages between the anatomical structures and physiology of the oropharynx (mouth and throat) and oesophagus, with control of the process by the central nervous system and the complicated network of the autonomic nervous system of the gastrointestinal tract (see below). This interplay explains why there are a number of disorders that are characterised by both neurological and gastrointestinal signs and symptoms (for example, Parkinson’s and Alzheimer’s disease, some encephalopathies (infections affecting the brain), herpes infections, some autistic disorders, some forms of motor neuron disease).
The normal process of swallowing changes in old age as anatomy and physiology change with ageing, including reduced muscle strength, reduced salivary flow rates and reduced taste acuity. Such age-related effects on swallowing, presbyphagia, typically do not cause serious problems and are largely compensated for. Presbyphagia may be considered similar to other age-related changes in eye-sight and hearing. It is, however, important to note when presbyphagia changes to dysphagia in need of attention, and to recognise that pre-existing presbyphagia may leave somebody more vulnerable to developing dysphagia.
A range of medications, often prescribed to the elderly but used across all ages, carry a burden of adverse effects that contribute to swallowing difficulties. Widely used medications with such adverse effects include
- sedative and neuroleptic agents, antiepileptic agents – reducing attention and oral movement command;
- steroids – reducing tongue and mouth strength, reducing oesophagus motility;
- anticholinergic agents and tricyclic antidepressants (amongst many other medications) – causing dry mouth, xerostomia;
- some antipsychotic agents – disturbing the pharyngeal phase of swallowing;
- bisphosphonates – disturbing the pharyngeal phase of swallowing.
The ways in which various medications can cause dysphagia are diverse. The mechanisms may be direct effects on the structures involved in swallowing (for example, antibacterial agents such as clindamycin or tetracyclines can lead to inflammation of the mucosa of the oesophagus through direct contact). More commonly, the effects are indirect and stem from the systemic effects of a particular medication. This is the case for many sedative and antiepileptic agents, antidepressants or neuroleptic agents. Adverse neuro-muscular effects of corticosteroids, including weakening of the muscular function of the swallowing apparatus, are a common medication-related myopathy and have been known for a long time (steroid-myopathy). Similar adverse effects have been described for statins (cholesterol-lowering agents). It is thought that medications (in particular multiple simultaneous prescriptions leading to cumulative adverse effects) are an under-recognised cause of dysphagia, or sometimes it may even be tacitly taken as an ‘unwanted effect’ to be accepted, and/or may be a core explanation for presbyphagia (see above).
Dysphagia in children is a special consideration and underlying causes are normally managed by specialised multidisciplinary paediatric teams, often with contributions from oral & maxillofacial surgery. Childhood-specific dysphagia causes can be
- anatomical – such as cleft lip & palate, some craniofacial malformations, malformations of the tongue, trachea (airway) or larynx, choanal atresia (blockage of the nasal passage), tracheoesophageal fistula (abnormal connection between trachea and oesophagus), some vascular malformations;
- genetic congenital conditions – such as trisomy 21 or 18, several craniofacial syndromes (for example, Apert, Pierre-Robin, Treacher-Collins syndromes, Chiari malformation), with dysphagia affecting approximately 50 % of children with such syndromes;
- neurological – such as central nervous system conditions and malformations (for example, cerebral palsy is almost always accompanied by dysphagia), some infections (for example, meningitis or some forms of encephalitis).
Apart from these conditions, other causes for dysphagia typically seen in adults also occur in children.
One way to classify the many different variants of dysphagia is by the location of the lesion / malfunction. Our main emphasis (see below) is on the oral and oropharyngeal space and associated forms of dysphagia. As a matter of completeness, we also briefly summarise dysphagia conditions affecting the oesophagus and the passage from the oesophagus into the stomach. Two functionally important locations along the gastrointestinal channel from mouth to stomach are the two ‘valves’ that enable respiration and smooth passage of food without aspiration. One of these ‘valves’ is located at the transition from the oesophagus to the stomach (the lower oesophageal sphincter), the other is at the entrance to the oesophagus from the pharynx (the upper oesophageal sphincter).
There are several mechanisms in place that separate respiration from swallowing, an indication of the physiological importance of protecting the airway and avoiding aspiration: aspiration can lead to pneumonia and can be a life-threatening consequence of dysphagia. The trachea (airway) and the oesophagus share space in the pharynx, and safe coordination & separation of swallowing and respiration are, therefore vital. This aspect of precise temporal control in the shared use of the pharyngeal space by the two processed is controlled by an area in the brain stem. Usually, respiration is briefly paused by swallowing in this centrally controlled mechanism, and swallowing is almost always integrated in the expiration cycle of respiration, following an ‘exhale – swallow – exhale’ pattern. In this way, the chances of liquid or solid food to enter the airway are minimised.
It is also useful to remember that only part of the oral phase of swallowing (control of the bolus and lip seal) is under voluntary control, all following stages of the swallowing process are involuntary (see below).
Diagnostic methods to investigate dysphagia
Similar to investigations into other symptoms with multiple potential causes, the first steps in the diagnosis of causes of dysphagia are a thorough medical history and medical examination. It is common that the perceived & reported location of a lesion / problem is situated well above the actual location of the problem area, such as a stricture. It is also common that symptoms exist that are not specific to dysphagia, or are not obviously related to dysphagia (for example, if coughing persists throughout the day, not only after eating) and hence are easy to overlook or misinterpret. The medical history, including any medications used and any relevant previous interventions (such as endotracheal intubation, tumour resection, extended periods of ventilation in intensive care, radiotherapy) usually informs the most logical & appropriate next diagnostic investigation. For example, if somebody reports increasing difficulties swallowing solid foods, it is most likely that a mechanical hindrance, such as a stricture or tumour growth, prevents food passage. In contrast, if from the start the swallowing of liquids and solids was affected, the dysphagia is more likely due to a motility problem.
Diagnostic methods include
- a number of different X-ray based investigations;
- a range of different endoscopic investigations, depending on location and suspected problem;
- biopsies , typically taken during endoscopy examinations;
- continuous pH (acidity) monitoring with sensors placed at different locations of the oesophagus to investigate reflux disease;
- measuring pressure with sensors (manometry) placed at different locations for the evaluation of mechanical parameters of swallowing / motility.
Broadly speaking, X-ray based imaging using contrast-enhanced approaches (‘barium swallow’) are most useful to depict structural problems interfering with the swallowing process. Endoscopic methods are very widely used in dysphagia investigations and mostly permit detailed inspection of the lining of the gastrointestinal tract (for example, to identify inflammation and/or ulcers), detection of food residuals, aspiration of food and/or saliva, and to identify safe food textures for oral food intake. Flexible fibreoptic endoscopy is also widely used to monitor progress of dysphagia treatment schemes over time. Most people have no problems tolerating such endoscopic investigations, the examinations are not particularly invasive.
Dysphagia associated with the oral and oropharyngeal space
Some acute inabilities to take food orally could be classed as a form of dysphagia. For example, mucositis occurring during radiotherapy may make oral food intake too painful to maintain oral feeding. Here we do not consider such acute problems (these are discussed in other relevant sections on the website). Instead we concentrate on chronic dysphagia. Significant chronic dysphagia is often underestimated and overlooked, despite its potentially life-threatening consequences. We briefly describe the normal swallowing control structures and mechanisms, describe different types of disorders (giving rise to different swallowing problems), and discuss aspects of dysphagia following major maxillofacial surgery as well as dysphagia following radiotherapy treatment to the head & neck region.
The swallowing control ‘centres’
Considering the neurological, normal control mechanisms of swallowing is particularly relevant to obtain an understanding of dysphagia associated with the oral and oropharyngeal space. In this anatomical region, the swallowing process is in part under voluntary control (during the oral phase), in part under involuntary control (swallowing associated with the oesophageal passage is solely under involuntary control). Different regions of the brain have different roles in the regulation of the swallowing process. Broadly, the brain stem region is responsible for the swallowing reflex and involuntary control, in addition to hosting the overall control centre for precise coordination and synchronisation of respiration and swallowing; the cortex region of the brain is in control of the voluntary stages of swallowing. Obviously, different lesions of the central nervous system (for example, a stroke or various degenerative conditions) cause different forms of oral and oropharyngeal dysphagia.
The overall central swallowing control further depends on a smooth communication flow with the peripheral nervous system. Information input to the central nervous system is provided by the afferent nervous system (mostly affecting sensitivity), information output from the efferent nervous system then enables the many different muscles involved in swallowing (mostly affecting motility). Nearly all cranial nerves are engaged in one, or both, of these information input/output functions. Swallowing-relevant, afferent nervous sensory input comes from cranial nerves I, the olfactory nerve (nasal mucosa); V, the trigeminal nerve with its many branches (anterior tongue, nasal cavity, sinus floor, palate, floor of the mouth); VII, the facial nerve (anterior tongue); IX, the glossopharyngeal nerve (posterior back of the tongue, part of pharynx); X, the vagus nerve (mucosa of trachea and oesophagus, taste buds, epiglottis). Swallowing-relevant, efferent nervous system output for motor response comes from cranial nerves V, VII, XII (the hypoglossal nerve) for the voluntary stages of the oral phase of swallowing, cranial nerves V, VII, IX, X, XII provide motor response for the pharyngeal phase of swallowing. Obviously, different lesions of the cranial nerves cause different forms of oral and oropharyngeal dysphagia.
Finally, execution of the various stages of the orchestrated swallowing manoeuvre is provided by approximately 30 pairs of muscles. Overall this is undoubtedly a highly complicated system – with advantages (resilience and multiple options to compensate difficulties) and disadvantages (multiple opportunities for things to go wrong and challenges for reconstruction).
Different types of disorders
Disorders leading to oral and oropharyngeal dysphagia can be broadly classed as structural, motility and sensitivity disorders, with degrees of overlap between these categories.
Structural disorders include
- changes to, and lesions of the mucosa;
- lack of symmetry of the oral cavity;
- scarring and fibrosis;
- atrophy of muscles;
- damage to cranial nerves;
- defects and/or dysfunction of the epiglottis (a flap of cartilage behind the tongue, which is depressed during swallowing to protect the airway) or hemi-laryngectomy (leaving the airway unprotected);
- tongue defects (bolus formation and transport impaired);
- defects / dysfunction of the soft palate (hyperrhinophonia (distorted speech with excess resonance in the nasal cavity), disturbed swallowing reflex and misguided bolus transport);
- consequences of hard and soft tissue trauma, including burns;
- pre- and/or post-operative tumour surgery / reconstruction;
- consequences of long-term intubation in intensive care.
Motility disorders (central or peripheral nervous origin) include
- reduced motility of larynx and/or hyoid bone (causing insufficient airway protection);
- reduced pharyngeal motility;
- poor glottis (part of the larynx, the vocal cords and the space between) function, leading to aspiration;
- iatrogenic damage from temporary paralysing agents (such as botulinum toxin alpha);
- insufficient synchronisation of swallowing and respiration processes;
- hyperkinesis / involuntary movement and spasm affecting velum and posterior pharyngeal wall (as a consequence of brain trauma);
- lack of velum motility and insufficient velopharyngeal function / closure (a potential consequence of oropharyngeal tumours, tonsillectomy of resection hypopharyngeal tumours).
Sensitivity disorders include
- lack of coordination of swallowing / respiration processes;
- reduced larynx sensation (impairs swallowing reflex, causes premature leakage of food into glottis, reduced coughing reflex leading to ‘silent aspiration’);
- retarded swallowing reflex;
- consequences of damage to cranial nerves, including
- olfactory nerve damage - disturbs triggering the swallow reflex and causes ‘spontaneous salivation’;
- trigeminal and facial nerve damage – disturbance of salivation and taste, difficulties with bolus processing and transport;
- glossopharyngeal, hypoglossal and vagus nerve damage – taste disturbance, lack of airway protection, difficulty with bolus transport;
- hypersalivation (may also be structural in nature, aspiration of saliva);
- degenerative neurological conditions such as Parkinson’s or motor neuron disease, stroke.
The underlying causes for all of theses disorders associated with oral and oropharyngeal dysphagia are numerous, ranging from trauma (neurological and otherwise), to neuro-degenerative conditions, congenital anomalies and malformations, signs & symptoms of tumours and other causes, to the consequences of treatment (see below).
Dysphagia following major maxillofacial surgery
Dysphagia caused by surgical interventions, either ablation or reconstruction are structural disorders (see above) by nature. Obvious examples would be partial or even total glossectomy. The role of the tongue in clearing the sulci and depositing a food bolus into the involuntary phase of swallowing in the posterior oro-pharynx is fairly obvious and very complex. Nothing we can do to reconstruct a tongue can simulate these multiple movements but the problem is, essentially, structural.
Dysphagia following radiotherapy to the head & neck region
There is a strong correlation between radiation dose applied to swallowing-related structures and dysphagia as a late and lasting adverse effect of radiotherapy applied to the head & neck region. Significant and lasting dysphagia develops in about 40 % of patients. Despite the now common use of intensity-modulated radiation schemes in attempts to spare important structures, long-term issues such as dysphagia are common. Long-term radiation-induced dysphagia is the result of inflammation, oedema, and fibrosis (including trismus). All of these conditions can, for example, impair the motility of the base of the tongue, or various pharyngeal muscles. Other motility issues such as impaired vocal cord motion can add to the problem (frozen larynx, increasing risk of aspiration). All of this is likely to occur on top of (often severe) xerostomia caused by radiation damage to the salivary glands. While xerostomia develops quickly during and after radiotherapy, it can take a considerable amount of time (of the order of years) for dysphagia caused by oedema and fibrosis to develop. This late-onset dysphagia may reach a stable plateau, or may continue to worsen over time. Dysphagia caused by the long-term structural damage from radiotherapy carries a significantly increased risk of aspiration, with a concomitant increased risk to develop aspiration pneumonia (sometimes repeatedly).
If radiotherapy was used in addition to surgery (see above), additional swallowing problems may exist. Combined chemo- and radiotherapy schemes tend to be accompanied by significantly increased dysphagia problems (in addition to other adverse effects).
Dysphagia associated with the oesophagus and transfer to the stomach
These forms of dysphagia clearly are not within the remit of oral & maxillofacial surgery and will be treated /managed by the appropriate specialists. However, a similar range of disorders to those causing oral & oropharyngeal dysphagia can be compiled for dysphagia associated with the oesophagus and transfer to the stomach. A major difference to oral & oropharyngeal dysphagia is the absence of voluntary nervous control of the passage beyond the pharynx. There may be some overlap between these forms of dysphagia and those associated with the oral & oropharyngeal space.
Structural disorders of the oesophagus include stenoses (narrowing) and diverticula (pouches). A stenosis might be caused by compression of the oesophagus by some growth adjacent to it, or within the oesophagus wall tissue, or by the narrowing of the passage way by thickening of the wall of the oesophagus (this can occur following long-standing inflammation, with gastro-oesophageal reflux disease the most common cause; or can be caused by scarring following radiotherapy in the region). Diverticula can develop in the region of the pharynx (Zenker’s diverticulum) or the oesophagus. These pouches may not cause any symptoms while they are small. However, a large diverticulum may act as a significant sac-like repository of undigested liquid and solid food, which then is regurgitated often long after eating.
Motility disorders of the oesophagus result from over- or underactivity of the normal strength and/or coordination of the contractions along the oesophagus that actively transport food along and into the stomach. Such abnormal behaviour may or may not be triggered by swallowing. For example, achalasia is a motility disorder where the lower oesophageal sphincter fails and most or all of the peristaltic motions are absent, leading to build up of food in the oesophagus. Oesophageal spasms represent abnormal and overly intense contractions of the oesophagus, with the most common cause gastro-oesophageal reflux disease.
Chronic dysphagia conditions affecting the oesophagus with unknown cause are referred to as functional dysphagia, a diagnosis reached by exclusion of all other known causes (inflammation, structural or motility disorders). It is thought that functional dysphagia may be associated with some neuropathy of the gastrointestinal involuntary nervous system.
Further reading: Diagnosis