One of my university assignments required me to research a new field of practice, and present the results as a proposal. I chose to write about Chronic Refractory Cough. Enjoy!
Defining Chronic Refractory Cough (CRC)
Cough is the most common symptom for which people seek ambulatory care in the United States (Hsiao, Cherry, Beatty, & Rechtsteiner, 2010). Physicians usually separate cough that is less than three weeks in duration (‘acute cough’) from that which persists for longer (‘sub-acute cough’ being three to eight weeks, ‘chronic cough’ persisting for longer than eight weeks). Respiratory physicians have developed a series of care guidelines for the management of cough, from which we can broadly categorise chronic cough etiologies (Irwin et al., 2006; Morice et al., 2004; Morice, McGarvey, & Pavord, 2006):
|Upper Respiratory||Upper Airway Cough Syndrome
|Lower Respiratory||Asthma & COPD
|Aerodigestive||Reflux (GERD)||Protein-Pump Inhibitors|
Management involves a careful balance between empirical pharmaceutical treatment and objective measurements or studies. It is often difficult to identify the precipitating cause, as these conditions do not always cause cough. For example, the prevalence of GERD in Australia is 10%, and only a minority of these patients will develop chronic cough (Knox, Harrison, Britt, & Henderson, 2008). However, in some patients the etiology of chronic cough is not identified, and the condition fails to respond to empiric treatment. In this case it is considered ‘refractory’.
Why is CRC refractory?
New insights into the nature of cough are able to explain CRC. Cough is primarily a defensive mechanism of the airway to prevent irritants or foreign bodies from entering the lungs. The traditional understanding of cough describes a mechanical or chemical irritant triggering an afferent receptor in the respiratory tract, which activates a diffuse ‘cough-centre’ in the medulla, which then directs the glottis to close against a build-up of sub-glottal pressure. The glottis relaxes, causing the expulsion of air at speeds approaching the speed of sound, which expels the foreign bodies and shears the irritants off the mucosa (Irwin et al., 1998).
A more complex understanding, informed by recent research, hypothesises irritants triggering a cortical ‘urge-to-cough’ sensation which can vary in intensity according to the nature of the irritant. Through repeated irritation or inflammation, these afferent pathways may be damaged, or the cortex may neuroplastically respond to lower the ‘cough-threshold’ (the minimum amount of a given stimulus required to make a cough unable to be suppressed) (Morice, 2010; Morrison, Rammage, & Emami, 1999). Also, the larynx may develop ‘urge-to-cough’ with stimuli that would not usually cause cough (Vertigan, Theodoros, Gibson, & Winkworth, 2007). Thus even if the initial cause of the hypersensitivity (reflux, infection, etc.) is resolved, the cough may remain due to the induced sensory neuropathy.
Nature and implications of the condition
People with CRC may cough on stimuli that do not usually stimulate cough, such as talking, lying down, eating or performing exercise; as well as displaying hypersensitivity to stimuli that can cause cough such as perfumes, smoke or cold air (Chung, 2014; French, Irwin, Curley, & Krikorian, 1998; Morrison et al., 1999; Vertigan et al., 2007). It is important to note that triggers are often so varied that it is impossible for patients to avoid all of them in their everyday lives.
Investigations have revealed that people with chronic cough report reduced physical, mental and social health, reduced vitality, and sometimes have worries regarding personal safety (Morice, 2013). More than half of chronic cough patient surveyed in a New York study reported depressive symptoms, which correlated with the presence of cough over the three months of the study (Dicpinigaitis, Tso, & Banauch, 2006).
A recent review suggested that the global prevalence of chronic cough, as measured by patient reports, was roughly 10% (Song et al., 2015). It is important to note that the condition is not localized to the Western Hemisphere. A limited number of small studies suggest that the proportion of those with chronic cough who fail to respond to specialist intervention is 12%-42% (McGarvey, 2008). While it is difficult to work with these figures to arrive at a prevalence figure for Chronic Refractory Cough, it is clear that there are a significant number of people who will experience this condition.
According to a worldwide survey, two-thirds of chronic cough patients are female, and the majority are aged 50-69 years, although in China the majority are aged 30-50 years, given the higher amount of environmental pollution (Morice et al., 2014). Females in general display greater difficulty in managing noxious stimuli, and this has been confirmed by studies of capsaicin challenges (Kastelik et al., 2002; Morice et al., 2014).
Populations suitable for specialist management
Not all chronic cough patients receive adequate investigations through primary care. General Practitioners should at least trial therapy for GERD, asthma or upper-respiratory infections before referring for specialist management. These therapies are commonplace, and present minimal risk to the patient. The GP should also investigate common environmental causes, and discuss possible lifestyle changes with the patient. For example, the patient could implement diet changes to manage GERD or cease smoking (Gibson et al., 2010).
Better research is needed to separate refractory chronic cough patients from those whose cough will resolve. As already indicated, chronic cough patients can have poor response to empiric treatments, and cough-sensitivity testing is unfortunately not a specific measure of CRC (Birring, 2011). Better measurements will present patients with a clearer pathway to CRC resolution.
Speech Pathology Assessment and Intervention
Speech Pathology management for CRC has been used for many years (Blager, Gay, & Wood, 1988), but there has been a recent increase in published research since the mid-2000s. Speech Pathologists (SPs) do not require specific qualifications to practice in this area in Australia; however, it is an emerging area of practice not rigorously covered in tertiary courses, and is only tangentially referred to in Speech Pathology Australia’s Scope of Practice (2015). SPs could gain competency in this area through professional development workshops, contact with expert clinicians, and targeted reading of the literature.
SP assessment would involve a case history from the patient’s referring doctor and the patient themselves detailing the characteristics of the cough, its triggers, severity, impacts on the person’s activities and participation, and previous management. Associated symptoms would be investigated, including the presence of comorbid middle airway dysfunctions, such as paradoxical vocal fold movement (Vertigan, Bone, & Gibson, 2013). Additionally, the SP would ask questions typical to voice patients, including level of hydration, alcohol and caffeine consumption, lozenge use, exposure to fumes, breathing style, and vocal behaviours and demands. Finally the SP should assess the patient’s candidacy for behavioural therapy by investigating their concern and their ability to adopt an internal locus of control.
Over the course of 2-3 sessions, the SP would deliver a four-pronged intervention as per Vertigan & Gibson (2012). The patient would be taught about the nature of cough, and that cough is not always productive (in both senses of the word), along with basic respiratory anatomy and physiology. Then, the patient would learn the control techniques, in much the same manner as learning fluency-shaping techniques in stuttering. They would learn to apply the technique for short periods of time in unchallenging situations before moving up a hierarchy. The specific techniques include controlled breathing through pursed lips, effortful swallows, gum-chewing, and sipping water.
The SP would also give the patient a generic vocal hygiene education to reduce laryngeal irritation; and finally, provide psychosocial counselling to build an internal locus of control for the patient, in order for them to view their cough as a behavior rather than as an affliction. Resolution of the condition is best measured by patient report against a valid measure of cough-related quality of life (Boulet et al., 2014)
The treatment agent in SP intervention is believed to be the cessation of the ‘vicious cycle’, in which repeated irritation causes more coughing, which in turn creates more irritation (Vertigan & Gibson, 2012). By ‘controlling’ the cough and minimising irritation, patients should be able to neuroplastically restore their cough thresholds.
If the SP intervention fails, the SP should consult with the cough team (a respiratory specialist, otolaryngologist, or possibly a psychologist), who would order specialised investigations or prescribe pharmaceutical management. Gabapentin, an analgesic, and amitriptyline, an antidepressant, are used for resolving neuropathic pain with recent investigations solidifying the evidence base for their use in chronic cough (Bastian, Vaidya, & Delsupehe, 2006; Jeyakumar, Brickman, & Haben, 2006; Lee & Woo, 2005; Ryan, Birring, & Gibson, 2012). It is important to note, however, that they will only relieve central neuropathies, not peripheral, and thus may not resolve all cases of CRC. Also, recent evidence suggests that patients’ CRC may return after the cessation of Gabapentin (Gibson & Vertigan, 2015). Results soon to be published show the increased efficacy of speech pathology and Gabapentin protocol compared with either intervention (Vertigan, forthcoming).
Evidence for SP intervention
A single-blinded, randomised controlled study of the speech pathology management program outlined above was undertaken, where the control group were given a placebo ‘healthy-lifestyle’ education program (Vertigan, Theodoros, Gibson, & Winkworth, 2006). Treatment dose was four one-on-one thirty minute sessions over two months. Participants rated cough, respiratory, voice and upper airway symptoms, as well as overall limitation on two five point scales of severity and frequency. Participants in the intervention group improved on all measures at a significantly higher rate than those in the placebo group. Dropouts were similar across groups, effect sizes were not reported, and no follow up was undertaken. Other teams have made similar findings with less robust study designs (Murry et al., 2010; Murry, Tabaee, & Aviv, 2004). There is a clear need for further research to investigate the treatment agent in SP intervention; that is, which of the four prongs is specifically efficacious in treatment.
 It should be noted that these figures vary greatly between studies, with a recent paper suggesting CRC occurs in up to between 0%-50% of specialist presentations – a range that is not clinically useful (Gibson & Vertigan, 2015).
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