White Paper by the European Society for Swallowing Disorders: Screening and Non-instrumental Assessment for Dysphagia in Adults

Screening is generally accepted as the first step in the management of dysphagia by identifying patients at risk for swallowing problems (see Fig. 1). Being identified as at risk of dysphagia following screening indicates the need for further assessment. A great variety of different types of screening has been described in the literature. Many screening tools consist of trial swallows using water in various aliquots or a range of different viscosities. Other forms of screening utilize combined protocols of trial swallows and pulse oximetry, pulse oximetry alone, evaluating clinical features (e.g. abnormal gag, voice alteration, or volitional cough), cervical auscultation, and elements of medical history (e.g. recurrent episodes of pneumonia or cough elicitation tests) [11, 12]. In addition, screening tools may use different endpoints to define being at risk, such as penetration, aspiration, pharyngeal delay, or dysphagia.

Screening tools using multiple swallow trials may differ in the order of selected viscosities or selected volumes per swallow trial. For example, the Toronto Bedside Swallowing Screening Test or TOR-BSST [13] consists of two steps; the first step is screening for abnormalities in voice quality and tongue movement, and the second step consists of ten consecutive teaspoons of water. Any failed item during either the first or second step constitutes a positive screen result and indicates an increased risk for dysphagia and a need to referral for assessment. Authors of water swallow screening tools may argue that the rationale for screening is solely to identify persons at risk of dysphagia and, therefore, no other consistencies need to be included[14].

Conversely, the volume–viscosity swallowing test or V-VST [15], another commonly used screening, uses three different viscosities (referred to as nectar, liquid, and pudding) and three volumes (5, 10 and 20 ml), resulting in a maximum of nine swallow trials. Whereas the TOR-BSST screens for being at risk for dysphagia only, the V-VST provides additional oral intake advice. Still, as only single trials are used per volume–viscosity combination, any advice on oral intake should be made with caution, as using a limited number of swallow trials can underestimate the aspiration risk in persons with dysphagia, especially when using boluses with a thin liquid consistency [16]. Even when a screening tool uses several trials of the same volume and viscosity, for example the Gugging Swallowing Screen or GUSS [17], any advice on oral intake should nevertheless be supported by findings from further assessment.

There is still no consensus on the order in which different viscosities should be offered when expanding the water protocol with, for example, thickened liquids, puddings, or solid boluses. Some authors start with thickened liquids using increased patient safety in terms of reduced frequency of aspiration as rationale, whereas other authors prefer starting with thin liquids referring to the heightened risk of residue when using higher viscosities [18]. Also, the use of different volumes may impact screening results; consecutive sips with large volumes in patients without overt airway responses or voice changes seem to rule out risk of aspiration, whereas small volumes with single sips indicate aspiration when clinical signs are present [14].

All patients at risk of dysphagia should be screened. Common populations at risk are frail older persons, stroke patients, patients with progressive neurological diseases (e.g. Parkinson’s disease or dementia), children and adults with non-progressive neurodevelopmental conditions (e.g. cerebral palsy), and patients with head and neck cancer [7, 19, 20]. Patients failing screening should be referred for further assessment by a dysphagia expert. However, patients having an established risk for dysphagia or manifest signs of dysphagia through case history may be referred for further assessment without being subjected to screening. If patients cannot be screened due to their cognitive state or health condition, screening should be postponed, usually resulting in recommended nil per os while waiting for screening. Some patient groups, however, may follow different screening and assessment pathways as no improvement in their condition is to be expected, for example, patients who may be at risk of dysphagia and have progressive cognitive decline (e.g. dementia). The lack of consensus and guidelines on how to manage these vulnerable populations result in moral dilemmas that need to be resolved on a case-by-case basis between healthcare practitioners and patients’ family. In comparison, screening is usually recommended to be performed within the first 24 h following the stroke [21]; however, there is no international consensus on what should be the critical timeframe for screening in other diagnostic groups.

Screening needs to meet the following feasibility criteria before being implemented in clinical settings: simple administration, use of non-invasive methods to minimize distress to patients, and straightforward to train clinicians involved [22, 23]. While most screening tools are freely available, some, like the TOR-BSST, can only be used after attending an online training module to improve standardization and consistency in rating.

Screening tools need to be valid, reliable, and show good diagnostic performance. Screening tools can be developed and validated for specific target populations (e.g. patients after stroke, patients with head and neck cancer or frail older persons). The use of certain screening tools may not be recommended in other patient groups than the populations for which the screen was originally developed and validated for; validity of a screening must be confirmed again when its use is extended to other clinical populations. Sufficient intra-rater, inter-rater, or test–retest reliability is often expressed by an intra-class correlation coefficient (ICC) or weighted Kappa equal to or greater than 0.70 [24]. Diagnostic performance of a screening tool is determined by comparison with a reference test, usually fiberoptic endoscopic evaluation of swallowing (FEES) or videofluoroscopic evaluation of swallowing (VFS). According to the international COnsensus-based Standards for the selection of health Measurement INstruments (COSMIN), this is also referred to as criterion validity [25]. The reference test is considered the ‘gold standard’ and hypothesized to have no false negative or false positive results. In other words, the ‘gold standard’ correctly indicates the presence of dysphagia when the person truly has dysphagia (true positives) and identifies subjects as not having dysphagia when they truly do not have dysphagia (true negatives). As such, it is not recommended to use another screening or clinical assessment as reference test unless considered a ‘gold standard’. Furthermore, both reference tests and screening tools may use different endpoints. For example, when administering a FEES, the occurrence of aspiration may be used as endpoint to confirm the diagnosis of dysphagia, whereas a water swallow screening may use coughing or a wet voice as endpoint for identifying a patient at risk of dysphagia. As different endpoints yield different diagnostic performance, clinicians and researchers must predefine and select endpoints before determining diagnostic performance.

Diagnostic performance comprises elements such as sensitivity, specificity, positive and negative predictive value, positive and negative likelihood ratio, and diagnostic odds ratio (Table 1) [26]. As applied to the topic at hand, sensitivity and specificity refer to how well the screening tool identifies the presence and absence of dysphagia, respectively, whereas predictive values are the probability that a positive or negative test result is accurate. As such, sensitivity and specificity provide clinicians information about which screening to select, whereas predictive values inform the persons being tested about the chances of actually having dysphagia.

Depending on work environment and requirements, different cut-offs for diagnostic performance may be used. For example, if assessment after screening is expensive or invasive, clinicians may prefer to minimize the number of false positives and use a cut-point with high specificity. Conversely, if the penalty for missing a case is high (e.g. the disease is fatal but can be treated successfully), a clinician may prefer to maximizing the number of true positives by using a cut-point with high sensitivity. In general, tests with high sensitivity have low specificity; they are good for identifying actual cases of the disease but often at the expense of high rates of false positives. For example, results from a meta-analysis showed that increasing volumes in water swallow tests resulted in higher sensitivity but lower specificity when screening for aspiration in stroke patients [27]. There are, however, no strict guidelines on the optimal cut-offs for diagnostic performance. Some diagnostic reviews only included screening tools with a high sensitivity (at least 70%) and at least a moderate specificity (at least 60%; e.g. [11, 12]). Even so, guidelines on what cut-off scores to use remain ambiguous.

A receiver operating characteristics (ROC) curve, a probability curve, visualizes the trade-off between sensitivity and specificity by presenting the true positive rate (sensitivity) as function of the false positive rate (100 minus specificity). Conversely, the area under the curve (AUC) can be interpreted as the average value of sensitivity for all possible values of specificity or the average value of specificity for all possible values of sensitivity [28]. AUC represents a measure of separability; how well is the model capable of distinguishing between two classes or groups, for example, between persons with or without dysphagia? The COSMIN guidelines stipulate that an AUC of at least 0.70 (or 70%) is required to provide evidence for sufficient criterion validity [24].

After a patient has been screened for dysphagia and identified as being at risk for dysphagia, further assessment is required (Fig. 1). Both ‘gold standard’ assessments VFS and FEES can diagnose aspiration (including silent aspiration) and other physiological problems in the pharyngeal phase. However, access to instrumental assessment may be restricted and no international consensus exists regarding which visuoperceptual or software-based measures to use for analysis of these video recordings. Moreover, there is insufficient psychometric evidence to recommend any individual measure as valid and reliable to interpret VFS and FEES recordings [29].

Another step after screening is non-instrumental clinical assessment by a dysphagia expert. In the process of clinical assessment of dysphagia, many different aspects may be distinguished, for example, medical history: conducting a physical examination; the subjective description of the swallowing problem or patients’ complaints [30]; and the expert’s clinical observations during the interview and examination process. Clinical assessment may have the following purposes, single or in combination: to identify possible causes of the swallowing problems; to estimate the safety of swallowing and risk of aspiration; to support decisions on oral or alternative feeding routes; to identify the need for further assessment (e.g. instrumental assessment); and to establish baseline data for future comparisons after intervention or during the course of a disease [22]. Clinical assessment may also address patient needs that are specific to certain clinical populations. For example, in patients with head and neck cancer, the effects of radiation and chemotherapy may be important and need to be described in detail.

Clinical assessment may refer to a large variety of assessments, each of which may be describing different aspects of dysphagia. In the absence of systematic reviews, textbooks and current opinion papers provide different overviews. While there is currently no comprehensive overview of clinical assessments, most literature seems to agree on the following four categories: 1) assessment of cognition and communication; 2) evaluation of the oral, laryngeal, and pharyngeal anatomy, physiology, and function (including cranial nerve examination); 3) oral intake and nutritional status; mealtime observations; and 4) intervention trials (e.g. bolus modification, postural adjustments and/or swallow manoeuvers) [22, 31].

Another form of non-instrumental clinical assessment involves patient self-report measures as part of the multidimensional assessment of dysphagia. Patient self-report measures target two distinct but related concepts: functional health status (FHS) versus health-related quality of life (HR-QoL). FHS refers to the influence of a given disease (e.g. dysphagia) on particular functional aspects, whereas HR-QoL is the unique personal perception of someone’s health, taking into account social, functional, and psychological issues [32].

Patient-reported measures play an important role in patient-centred healthcare and can improve communication, patient engagement, and self-efficacy as patients may be more involved in goal setting [33‐35]. The use of a patient-reported measure, however, may be limited by patients who experience cognitive and/or language comprehension deficits. Recently, a framework (patient-reported outcome measures or PROM-cycle) was developed to support the selection and implementation of patient-reported measures in individual patient care and for quality improvement [35]. The PROM-cycle describes eight steps necessary for systematic selection and implementation of PROMs in a cyclic approach and provides links to, for example, relevant tools and existing guidelines, examples from clinical practice and methodological considerations.

Patient self-report measures in dysphagia often combine both FHS and HR-QoL in the same measure, even though both are considered two distinct concepts. Consequently, disease-related functioning cannot be distinguished from disease-related quality of life as subjectively experienced by patients. Further, psychometric reviews on patient self-evaluation (e.g. [36, 37]) and psychometric evaluations on most commonly used self-report measures in dysphagia (e.g. [38‐42]) identified that all existing measures have either poor psychometric properties or lack comprehensive evaluation and reporting of psychometric properties. This flags an urgent need for research. For example, even though the Eating Assessment Tool (EAT-10) is one of the most commonly used FHS measure in dysphagia, recent evidence using contemporary Item Response Theory¹ (IRT; Rasch analyses [43, 44]) did not support its use in either research or clinical practice [38, 40‐42]. Another frequently used FHS questionnaire is the Sydney Swallow Questionnaire (SSQ [45]), which is yet to be evaluated using IRT.

Among those self-report measures mainly targeting HR-QoL are the Swallowing Quality of Life questionnaire (SWAL-QOL [46]), the Dysphagia Handicap Index (DHI [47]), the Deglutition Handicap Index (DHI [48]), and the MD Anderson Dysphagia Inventory (MDADI [49]). The SWAL-QoL, like the EAT-10, is one of few measures that has been evaluated using Rasch analyses. As an outcome of the evaluation, it was recommended to further investigate the SWAL-QoL’s underlying structure and psychometric characteristics prior to continued clinical use [39, 50]. For most self-report measures, however, even though their use is common practice, their psychometric robustness is yet to be established using IRT [36, 37].

The use of self-report measures for oral health has gained importance in recent years. Poor oral health and concomitant dysphagia are important risk factors of aspiration pneumonia [51]. Oropharyngeal colonization by respiratory pathogens has shown to play a key role in the pathophysiology of aspiration pneumonia [52‐56]. A recent systematic review reporting on patient-reported measures for oral health in adults identified 20 English-language multiple-item questionnaires summarized into four domains: oral function, orofacial pain, orofacial appearance, and psychosocial impact [57]. Examples of frequently used self-report measures in oral health include the Oral Health Impact Profile (OHIP [58]) and the Oral Health Questionnaire for Adults [59]. Most self-reported measures in oral health, however, need further psychometric evaluation before supporting their implementation in healthcare and research [57].

Given that gastroesophageal reflux disease (GERD) is common in populations presenting with dysphagia [2, 60, 61], self-report on GERD may form part of dysphagia assessment. Many examples can be found in the review by Bolier, Kessing [62] including, for example, the widely used and validated GERD Impact Scale (GIS [63]) and the Reflux Disease Questionnaire (RDQ [64]). Still, in the absence of further psychometric evaluations, many of these measures may not meet psychometric quality criteria [65].

Before assessing the anatomy and physiology of the swallowing act, some higher cortical functions that act as precursors to oral feeding need to be evaluated. These include, but are not limited to, the patient’s alertness, responsiveness, cognition and language skills, as well as head and trunk control (i.e. motor control) [66]. In the absence of standardized formal assessments, input–output reasoning will inform further clinical assessment of functional anatomy (Table 2–3) whereby innervation (input) from a muscle or functional groups of muscles (effectors) will, in turn, result in deglutition-related actions (output).

A strict order of events provides clinical markers that guide clinicians during assessment with a functional–anatomic pathway of motor outputs activated by sensory inputs (Table 2) [67]. Therefore, the anatomy and physiology that underpins the swallowing act need to be understood to allow for the assessment thereof. Swallowing is a highly integrated neuro-sensorimotor function, realized by organs (effectors) affiliated with different systems and inter-linked with other functions, so that swallowing, breathing, and phonoarticulation alternate according to hierarchically correlated pathways [68]. Swallowing is the result of external (sight and smell) and internal sensory stimuli (touch, temperature, and taste), which converge at the meduallary swallowing centre, from where the motor efferents of the bulbar cranial nerves (CNs) start: CN V (Trigeminal nerve: motor), CN VII (Facial nerve), CN IX (Glossopharyngeal nerve), CN X (Vagus nerve), CN XII (Hypoglossal nerve), and cervical spinal nerves C1-C3. The CN XI (accessory nerve) carries motor fibres for the sternocleidomastoid muscle and trapezius muscles (spinal root), and parasympathetic preganglionic visceral fibres (cranial root) that join the CN X reaching the soft palate, pharynx, larynx, and oesophagus. The brainstem swallowing centre is widely connected and receives cortical, subcortical, thalamic, limbic and cerebellar descending modulatory afferents, which transform the semi-reflex nature of swallowing into spatiotemporal integrated muscular contractions (muscular patterns) [5]. The neurological structures (including cortex, extrapyramidal and pyramidal system, and cranial nerves) are contained in the neurocranium (protective shell surrounding the brain and brain stem), while the swallowing effectors are contained in the viscerocranium (skeleton supporting facial structure). At this level, the upper parts of the respiratory and digestive tract are arranged in parallel and conjugate in the pharyngeal cavity, which becomes a common pathway for both air and bolus transport. In this way, the pharynx acts alternately as an organ of the respiratory tract (chamber for air passage) as well as an organ of the digestive tract (peristaltic contracting chamber for bolus passage).

Anatomy of the upper digestive tract allows the organization of functional chambers operating in a concatenated series [69]. In the oral cavity, the bolus is prepared (minced and mixed with saliva) as a consequence of coordinated actions between facial muscles, cheeks, teeth, jaws, tongue, and oral floor muscles [70]. When the bolus is transported into the pharyngeal cavity, a reflex reconfiguration of the pharynx occurs; the oropharynx transforms from a respiratory pathway to a swallow pathway [71]. The pharynx acts as a digestive lumen, generating contractile and peristaltic activities with the aim of transporting the bolus to the oesophagus [72]. A strict hierarchy between vital primordial reflex activities determines the arrest of respiration (apnea), thus allowing the pharyngeal transportation of the bolus [73]. The reconfiguration of the pharynx is defined by glossopalatal opening, velopharyngeal closure, upper and anterior hyoid laryngeal excursion, and upper oesophageal sphincter opening.

Articulation and voice quality are checked during speech and sustained vowel production and provide information about vocal fold or glottis closure. Furthermore, facial appearance and expression may indicate concerns about orofacial musculature, presence of surgical scarring, asymmetry, and inadequate labial seal (drooling). Touch, temperature, and taste sensibility can be tested on the lips, mucosa of the oral cavity, tongue (body, base, margins), fauci, soft palate, and posterior wall of the oropharynx using low-tech devices such as a wisp of cotton or tongue blade. The same low-tech devices can be used to test thermal and gustatory sensibility by wetting them in hot or iced water, or in salty, sweet, bitter, sour, or sparkling solutions.

Tone and strength of the tongue can be assessed by eliciting resistance against a tongue blade, while mobility is assessed by administering non-articulatory or articulatory praxis tasks. The opening of the jaws (temporomandibular joint) is closely examined and masticatory muscles are evaluated for its praxis and strength. The pterygoid muscles are tested during lateral mandibular movements with the jaw applying resistance against a hand, while the masseter and temporal muscles can be palpated during contraction. The symmetrical soft palate movement is evaluated using a simple articulatory task (i.e. by sustaining the vowel /a:/) or during the process of testing sensibility. The gag reflex can be elicited by stimulating the back of pharynx with a tongue blade/probe. Finally, the presence of the pharyngeal reflex is elicited by asking patients to perform a dry swallow while the clinician holds three fingers on the external hypo-laryngeal axis; the index finger is placed on the hyoid bone, the middle finger is placed on the thyroid notch, and the ring finger is placed on the cricoid ring. There should be an antero-superior displacement of these structures of about 2 to 2.5 cm during a dry swallow. Table 3 provides additional examples of clinical assessment of functional anatomy and physiology of the swallowing act.

A clinical swallowing evaluation (CSE) is typically performed after screening for swallowing problems to provide additional information to ascertain the relative risk for aspiration and to direct clinical decision making [74]. CSE findings are important in determining whether an instrumental assessment may be required (if not already performed) and to decide which compensatory strategies and postural manoeuvres need to be prioritized for trialling to inform dysphagia therapy planning and patient management. At least a tentative diagnosis must be made and a management plan agreed upon following a CSE [31]. However, aspiration and other physiological problems in the pharyngeal phase of swallowing can only be diagnosed through directly observation using instrumental assessments [75‐77].

The initial step in a CSE is to compile a thorough case history with the patient and/or carer. This involves a careful review of the medical history, if available, a history of the present condition (e.g. onset, duration of difficulties, symptoms), current swallowing status (e.g. method of oral intake and current diet, strategies that help swallowing, easiest and most difficult food consistencies to swallow), and factors that might influence management (e.g. comorbidities, cognition, food restrictions and nutritional status, presence of gastroesophageal reflux, and cultural preferences) [30]. Common examples of the many available measures used while compiling a case history are the Functional Oral Intake Scale (FOIS; [78]) and the Mini-Mental State Examination (MMSE; [79]) or Mini-Cog [80] to screen for cognitive impairment.

After compiling the case history, the clinician forms a preliminary clinical hypothesis that is tested during ensuing assessment. Only a few standardized CSE tests are available across dysphagia populations. The Mann Assessment of Swallowing Ability (MASA [81]) is an example of a standardized CSE. The MASA was validated on stroke patients and has adaptations for patients with head and neck cancer (MASA -C [82]). While conducting a CSE, the clinician also completes a clinical observation of the patient noting body posture, head posture at rest, level of alertness, and ability to follow assessment instructions, upper respiratory tract secretions, and the patient’s ability to manage his/her saliva. In addition, an orofacial examination is conducted that includes a cranial nerve examination. Oral health may be assessed using a measure such as the Oral Health Assessment Tool (OHAT [83]).

Trial feeding is only considered an appropriate management strategy if the patient has an adequate voluntary cough and is able to manage his/her own secretions. If, however, the patient is drowsy, medically unstable, and unable to swallow saliva requiring suctioning, then trial feeding is deemed too high risk and should not be attempted. Self-feeding is preferred over feeding by carers or health care providers, to mimic typical eating and drinking patterns. As mentioned earlier, there are opposing views regarding which consistency to trial first. Some clinicians prefer to begin trials with small 5 ml volumes of water, gradually increasing the volume before moving to thicker consistencies. The rationale is that water, if aspirated, combined with good oral hygiene will be absorbed into the lungs without the immediate risk for the development of pneumonia [84, 85]. Other clinicians prefer to start with thickened consistencies so as to reduce the risk for aspiration [15]. Trials with fluids that promote sensation, for example carbonation and sweet and sour bolus, may be included in CSE [86‐88]. The temperature of the bolus may also be manipulated with colder boluses used to increase sensation [89]. Thicker consistencies may be trialled later as they may give rise to residue in the pharynx which, in turn, can lead to aspiration [18]. When assessing chewing it is important to evaluate the patient’s ability to manage solids and to identify risk of choking also. Assessments such as the Test of Mastication and Swallowing of Solids (TOMASS [90]) may be useful.

When possible, a CSE should also include mealtime observation. This is particularly useful in patients with cognitive impairments where feeding and swallowing difficulties may be influenced by fluctuating levels of attention, fatigue, or environmental factors (e.g. background noise or other distractors). Observations such as the patient’s ability to self-feed, the need to use adaptive eating utensils, duration of the meal, and the presence of fatigue are noted. Examples of available standardized CSEs based on mealtime observation are the McGill Ingestive Skills Assessment (MISA [91]) for older persons with feeding difficulties, and the Dysphagia Disorder Survey (DDS; [92]) developed and validated for persons with developmental disabilities. Both measures have demonstrated promising, robust psychometric properties [91, 93, 94].

During the CSE, individualized trials are conducted to investigate the effectiveness of compensatory strategies the person may already have put in place or to test new strategies and examine which are most effective for safe and efficient oral intake. Compensatory strategies comprise changing what the person eats (i.e. diet modification) and changing how the person eats (e.g. head posture, alternate liquid/solid swallows, volume control). The efficacy of implementing adaptive equipment (e.g. beakers, modified spoons, straws) in promoting safe oral intake should also be examined.

Ancillary to conducting CSE is evaluation such as pulse oximetry and cervical auscultation. Pulse oximetry measures peripheral capillary oxyhemoglobin saturation and is used to detect a decrease in saturation, which is indicative of aspiration during swallowing [95]. Cervical auscultation is hypothesized to differentiate between normal and abnormal swallowing by listening to the sound of swallowing and swallowing-related respiration using a stethoscope placed on the neck [96]. However, there is contention regarding diagnostic accuracy of pulse oximetry in predicting aspiration and current evidence does not support its use [95]. Cervical auscultation, although commonly used, is equally contentious and there is limited evidence to support its use [96].

Limitations of the CSE are that protocols vary and that there is variability in practice even within the same clinical settings and between populations [97‐99]. However, its key strength is providing low-cost clinical information to the multidisciplinary team in the immediate management of patients with dysphagia, especially if clinical teams do not have access to instrumental assessments.

A core outcome set (COS) is an agreed minimum set of outcomes that should be measured and reported in clinical trials of a specific disease or target population [10]. When selecting outcome measures as part of a COS, four criteria need to be considered [10]. First, both the construct to be measured (e.g. FHS, HR-QoL) as well as the target population (e.g. age, diagnosis) must be clearly defined. Second, existing measures must be identified by, for example, performing literature searches or using recent systematic reviews. Third, the quality of all measures must be evaluated both in terms of quality of psychometric properties as well as feasibility for administering the measure within particular setting. Fourth, one measure must be selected for each outcome or construct in a COS (Fig. 1).

The COSMIN group established an international consensus-based taxonomy, terminology, and definitions of measurement properties for health-related patient-reported outcome measures [25]: guidelines for using the taxonomy, including a standardized appraisal tool for rating methodological quality of psychometric studies [100], criteria for evaluating psychometric quality of assessments [101, 102], and a rating system for synthesizing and grading psychometric evidence [101, 102]. The taxonomy distinguishes nine psychometric properties across three domains (Table 4): validity (content validity, structural validity, cross-cultural validity, hypothesis testing for construct validity and criterion validity), reliability (internal consistency, reliability and measurement error), and responsiveness. When selecting an assessment, all nine psychometric properties are considered when identifying the assessments with the most robust psychometric properties.

Assessments that have poor psychometric properties should not be used in either clinical settings or research. Minimum requirements for including an outcome measure in a COS are high-quality evidence for good content validity and good internal consistency [10]. However, as recent psychometric reviews have identified missing or indeterminate evidence for many psychometric properties of existing assessments in dysphagia (e.g. [29, 36, 37]), often only preliminary conclusions on the psychometric robustness of the assessments can be drawn based on current available psychometric evidence in the literature.

Content validity, the degree to which the content of an assessment is an adequate reflection of the construct to be measured, is considered the most important psychometric property within the COSMIN taxonomy [102]. Concerns around content validity are raised when assessments that have been developed and validated for specific target populations are used in different populations. For example, the MD Anderson Dysphagia Inventory (MDADI) is a dysphagia-specific quality of life questionnaire targeting patients with head and neck cancer [49], whereas the Dysphagia in MUltiple Sclerosis questionnaire (DYMUS) is a FHS self-report assessment for adults with multiple sclerosis [103]. Assessments like the MDADI and DYMUS that have been developed and validated for a specific clinical population cannot be used in another population without the risk of compromising its content validity [102]. For an assessment to have good content validity [102], all items need to be aligned with the construct of interest in a specific population and context of use (relevance), all key concepts of the construct need to be covered (comprehensiveness), and instructions, items and response options need to be understandable to the target population as intended (comprehensibility).

Problems may also occur when using a translated version of an original assessment, without undertaking the required steps to ensure good cultural validity. The proposed framework of translation by Koller, Kantzer [104] is based on a review of influential translation guidelines and summarizes the reconciliation processes that needs to be undertaken when translating measures. The framework stipulates that through a process of reconciliation, two or more independent forward translations are merged into one single translation using decision criteria on comprehensibility, cultural appropriateness, grammar, and use of relevant and consistent terminology. Next, cross-cultural validity needs to be determined by comparing the performance of items from a translated or culturally adapted assessment with the original assessment version [24].

Finally, aspects of feasibility need to be taken into consideration when deciding on which assessments to select for measuring outcomes. Feasibility refers to the practicability of using an assessment in its intended setting, taking into account constraints of time, money, and interpretability [10]. Other important factors related to feasibility include, for example, patient’s cognitive functioning and physical ability, patient’s and clinician’s ability to comprehend items, ease of administration, duration of administering the assessment, simplicity of score calculation, accessibility of required equipment in different settings, copyright requirements, and associated costs to acquire and administer the assessments [10]. Another consideration include administering, where appropriate, assessments via telehealth instead of face-to-face to increase accessibility to healthcare in rural and remote areas [105], to increase service reach, reduce costs [106], and more recently to continue providing safe health services during the COVID-19 pandemic.

Where access to instrumental assessment is restricted, the use of clinical assessments becomes exponentially important when evaluating patients’ illness trajectories. There are many screening and non-instrumental assessments available for evaluating dysphagia in adults (see Table 5). However, even though measures may be part of daily clinical practice, their use may not be warranted due to poor diagnostic performance or lacking robust psychometric properties.

Therefore, based on this ESSD white paper, the following recommendations are made (Fig. 1):

There are great challenges for future research in the screening and assessment of dysphagia in adults:

Instrument development and international consensus will enhance research designs and outcome measurement in future clinical trials and subsequently lead to improved health care pathways for patients with dysphagia. There is a need for standardized screening and assessment, and consistency in terminology and definitions used in research and clinical practice. When addressing the validity, reliability, and responsiveness of outcome measures, both measurement properties and criteria for good psychometrics should be defined (e.g. the COSMIN framework). Finally, when referring to dysphagia, a common language is needed to define its symptoms and promote consistent use of terminology in screening, assessment and interventions.