Coughing Triggered by Mechanical Stimulation Suggests New Type of Cough Sensitization

Patient responses to mechanical stimulation of somatic points of cough suggest that the central convergence of stimuli originating from different somatic and/or visceral areas facilitating the cough reflex is associated with the genesis of chronic cough, according to a study recently published in Respiratory Medicine.

These findings may disclose a potential "novel paradigm of cough sensitization," said the authors.

Researchers previously documented a case of a patient with chronic cough who complained of an urge to cough (UTC) and/or coughing triggered by normally innocuous stimuli involving light pressure on the tissues of the neck or chest.

Researchers conducted a study to further investigate features of this cough paradigm in patients with chronic cough and control subjects.

The study included 58 consecutive chronic cough adult outpatients without a history of recent respiratory infections and 34 healthy, age and gender-matched nonsmokers. Researchers collected demographic data from all participants.

Patients were asked to rate the magnitude of the disturbance caused by their cough using a 0-9 modified Borg Scale, referred to as their cough score.

Additionally, researchers attempted to evoke coughing and/or the UTC with finger pressure on discrete areas of the chest wall and neck as well as by encouraging full vertical extension and flexion of the neck. Any area on the upper trunk or neck that gave rise to an urge to cough sensation or overt coughing in response to mechanical actions such as pressure, flexion, or extension was determined as a somatic point for cough.

Participants with at least 1 somatic point of cough or no identifiable somatic points of cough were classified as being somatic point of cough-positive or -negative, respectively.

Researchers found that these mechanical actions evoked coughing or UTC in about 50% of patients with chronic cough. Conversely, the control subjects did not report an urge to cough or cough with mechanical action on any occasion. However, pressure on the sternal bone did evoke light pain in 9 control subjects (26.7%).

Patients were found to have a median cough duration of 2 years and their mean (SD) cough score was 5.4 (1.08).

Sternal pressure evoked pain in 14 patients (24.1%). The somatic point of cough-positive subgroup had a mean (SD) cough score of 5.9 (1.8). The subgroup of somatic point of cough-negative patients had a similar mean (SD) cough score, 5.0 (1.7).

Both subgroups experienced similar prevalence of pain sensations.

The most frequently identified somatic points of cough were the jugular notch as well as neck flexion or extension. The magnitude of responses was similar among all somatic points of cough. However, pressure on the sternum and spine were seldom effective. Sternal pressure evoked pain in approximately the same percentage of normal subjects and patients with chronic cough, suggesting that this response is likely unrelated to common cough.

Researchers found that coughing and urge to cough were reproducible (kappa test = 0.84; 95% CI, 0.78–0.96). All responses were abolished by cooling of relevant areas with dry ice.

These findings confirmed researchers’ previous observation of a chronic cough phenotype with urge to cough and/or coughing evoked by stimulation of specific somatic points.

While these findings do not contradict the notion of cough as a vagally-mediated reflex, they suggest central convergence of stimuli originating from different somatic and/or visceral areas facilitating the cough reflex (ie, central reflex sensation).

“The results may disclose a novel paradigm of cough sensitisation possibly involving central convergence of somatic and visceral neural stimuli,” wrote the authors.

Such convergence has been implicated in referred pain, pain perceived at a location other than the site of the painful stimulus.

Overall, the authors suggest that the large percentage of somatic point of cough-positive patients points to a relevant role of this symptom in the origin and/or persistence of chronic cough.

However, the reason urge to cough and/or cough can only be induced by mechanical stimulation of specific somatic areas remains unclear.

The authors encourage further investigation of the possible impact of this novel cough paradigm on the clinical history of patients with chronic cough, especially difficult-to-treat chronic cough.

Reference

Mannini C, Bernacchi G, Bonti V, et all. Somatic points for cough and urge to cough in chronic coughers. Respiratory Medicine. Published online July 13, 2022. doi:10.1016/j.rmed.2022.106929