Chronic coughing is defined as coughing that lasts more than 8 weeks and affects 4-10% of the general population. Individuals who have never smoked yet have a persistent cough are frequently diagnosed with asthma, gastroesophageal reflux disease, or upper airway cough syndrome.
Although treating the underlying causes of coughs can assist the vast majority of people, it is becoming increasingly obvious that a sizable minority of people will continue to cough despite standard medical therapy. These persons are commonly diagnosed with refractory chronic cough. Despite intensive investigation, the core reason for a small proportion of individuals’ chronic cough remains unexplained.
According to a study published in eClinical Medicine, chronic cough patients frequently describe throat pain and coughing fits in reaction to seemingly benign stimuli such as laughing, strong odors, and changes in the surrounding temperature.
Some writers associate these signs and symptoms with a sensory imbalance and label the disorder “cough hypersensitivity syndrome.” Sensitization of cough mediation circuits in the peripheral and/or central brain might explain the varied clinical manifestations of chronic cough.
Patients with chronic cough commonly report an urge-to-cough (UTC) or overt coughing in response to mechanical stimuli that work on specific parts of the neck and upper trunk, which may be explained by sensory dysregulation. The purpose of this study was to look at the frequency and clinical importance of somatically triggered cough in a non-selected cohort of chronic coughers.
Somatically induced cough is characterized as a cough and/or feeling of an upper airway obstruction (UTC) triggered by mechanical stimuli, especially finger pressure on upper chest and neck areas.
To put this to the test, researchers predicted that those with sensory dysregulation, such as those who have chronic coughing due to somatic evocation of cough, will have distinct clinical outcomes. A recent study conducted in Italy has found that somatically evoked cough (SPC) or upper trunk cough (UTC) is prevalent among females suffering from chronic cough, and it suggests a mechanism of central sensitisation that facilitates the cough reflex.
The study is the first to investigate the clinical relevance of SPC or UTC in a real-life population of adult patients with chronic coughs referred to a tertiary care center in Italy. The results confirm previous observations regarding a high percentage of SPC+ individuals among chronic coughers (particularly females), the anatomical distribution of SPCs in the upper trunk and neck, and the characteristics of the evoked responses.
The study also found that symptom-driven treatments of cough-associated symptoms almost always resulted in a marked reduction of symptoms other than cough itself in both SPC+ and SPC- patients. However, SPC+ patients failed to display a consistent reduction in cough score over the 6-month follow-up period. The percentage of non-responsive patients was almost three times higher than in the SPC- subgroup.
The researchers suggest that sensitization of peripheral and central neural pathways mediating cough is the fundamental mechanism underlying the cough hypersensitivity syndrome. The study’s findings suggest the role of a central sensitisation mechanism in facilitating the cough reflex, which might share similarities with the cough reflex sensitisation promoted by central convergence and synergy of different types of terminal fibers.
In SPC+ patients, activation of mechanically sensitive endings via finger pressure or functionally equivalent maneuvers might increase tachykinin concentration at the NTS level, thus facilitating the perception of an UTC or overt coughing by otherwise ineffective stimuli such as talking and laughing or even, in some instances, the chest wall and respiratory muscle movements of breathing.
The study has some limitations, including the involvement of body areas that are anatomically and functionally different, but it provides valuable insights into the neurophysiological basis of clinical forms of chronic cough.
The researchers suggest that mechanisms underlying nociception and cough may share similar features leading to the development of pain and cough hypersensitivities, and these mechanisms might constitute the neurophysiological basis of clinical forms of chronic cough, of which SPCs may represent a clinical hallmark.