Clinical Aspects of Chronic Idiopathic Postnasal Drip: An Entity Not to Be Overlooked

Discussion

CIPND. The authors have reported the clinical aspects of patients with CIPND. It is noteworthy to mention that the term ‘chronic idiopathic postnasal drip’ is not widely used but rather a novel denomination. In contrast, the symptom of postnasal drip, or ‘post-nasal catarrh’, is not new. The first modern medical record of the symptom dates back to 1794 (2, 3). However, it is notable that many papers and articles cite Dobell, who described ‘post-nasal catarrh’ extensively (4). Yet, with the emergence of the term ‘postnasal drip syndrome,’ the focus on the disease seemed to shift. The term ’postnasal drip syndrome’ was initially introduced to explain chronic cough in patients, thus it was never the exact same condition as ‘post-nasal catarrh’. However, as ‘postnasal drip syndrome’ became familiar among physicians, aspects of the concept of ‘post-nasal catarrh’ were partially incorporated, leading to confusion in terminology Consequently, some researchers began describing patients with postnasal drip symptoms as ‘postnasal drip syndrome’ patients (5-8). The authors aimed to resolve the ambiguity by avoiding the use of the term ‘postnasal drip syndrome’ and hoped to prevent confusion among readers. Also, we suggest using ‘postnasal drip’ to clearly describe patients in such conditions.

As described in the introduction, there are chronic postnasal drip patients without a clear diagnosis. The authors selected these patient group as a single entity and analyzed its clinical aspects. Since it is a single-center study, most of the patients underwent certain routine clinical evaluation and treatment including 1) first-generation antihistamine-decongestant prescription; 2) exclusion of other diseases. This allowed the authors to include patients to the retrospective cohort with less risk of misdiagnosis and bias.

Clinical features of CIPND. The patients with CIPND presented median symptom severity of seven in the visual analogue scale. This result suggests that this entity, which has not been of interest recently, is causing considerable discomfort to patients.

Cross-analysis between associated symptoms and postnasal drip viscosity showed that patients with serous drip presented more rhinorrhea, whereas those with mucoid drip presented more throat discomfort. However, these results are based on subjective judgement, and it is unclear whether the accompanying symptoms vary depending on the true viscosity of the postnasal drip or if patients have just described the nature of postnasal drip based on the accompanying symptoms. There is a report showing that different viscosity of artificial mucus did not reproduce the postnasal drip symptoms of rhinitis patients, and the patients had an increased sense of postnasal drip compared to the control group (9). In contrast, others reported that patients with postnasal drip showed changes in mucus viscosity and mucociliary clearance (10).

Of the patients, 30.3% presented cough, a prevalence higher than that observed in the general population (11). However, the relationship between postnasal drip and cough is still controversial. Even if we expand our scope to patients with non-idiopathic postnasal drip, the direct relationship between cough and drip is not clear. Early researchers believed that coughing in patients with postnasal drip occurred due to mechanical or chemical stimulation in the respiratory tract by the changed properties or increased amount of nasal mucus (12). However, several studies suggest that changes in the nasal mucus do not cause cough directly (6, 9, 13). Some researchers suggested cough hypersensitivity syndrome or sensory hyper-reactivity to explain chronic cough in patients with postnasal drip (14, 15).

Treatment response. In this study, 71.6% (58/81) of CIPND patients who received first-generation antihistamines and nasal decongestants reported a subjective treatment effect of fair or better. The American College of Chest Physicians (AACP) has recommended the empirical prescription of first-generation antihistamines-nasal decongestants for upper respiratory cough syndrome (previously, known as postnasal drip syndrome), when the cause is not clear (16). However, this recommendation is based on the results of a study targeting the improvement of cough in patients with chronic cough. Treatment effect of this combination treatment on postnasal drip symptoms was reported only in a single study targeting common cold patients, which showed that cough and postnasal drip improved significantly through combined treatment (17). To the best of the authors’ knowledge, this study is the only one reporting the treatment effect of first-generation antihistamines and nasal decongestant combination therapy in patients with CIPND. There are few other studies discussing the treatment effect on postnasal drip symptoms. One such study reported the treatment effect of proton pump inhibitors on postnasal drip, which significantly reduced the symptom in the treatment group (18). Some studies focused on the treatment of post-nasal drip symptoms in rhinosinusitis (8, 19). Therefore, a prospective, placebo-controlled study is needed to guide treatment.

The mechanism underlying the efficacy of first-generation antihistamines in the treatment of postnasal drip symptoms in CIPND patients is not clear. However, it is presumed to be similar to the mechanism by which they suppress cough in patients with post-nasal drip syndrome (or upper airway cough syndrome). First-generation antihistamines are known to suppress coughing through complex processes including not only inhibition of peripheral histamine receptors, but also sedation, anticholinergic action, binding to non-histaminergic receptors, and inhibition of central histamine receptors (20). There is also a report suggesting a similar neurological pathway involved in itching and coughing. It appears that the action of the above-mentioned first-generation antihistamines may have relieved postnasal drip symptoms through a similar inhibitory process (21).

Symptom re-occurrence and factors. CIPND patients with nasal stiffness showed significantly higher rate of symptom re-occurrence. It is well known that most patients complaining of nasal stiffness have anatomical factors in general (22) and considering that a significantly higher proportion of these patients experienced symptom recurrence within 24 hours of drug discontinuation, anatomical factors may have caused postnasal drip symptoms.

Limitations. The initial rule-out diagnosis of diseases such as laryngopharyngeal reflux relied on subjective outcomes, which may have introduced bias. Also, in the treatment outcome analysis of first-generation antihistamine and decongestant, there was no standardization of drug dosage and duration. Randomization or a control group was also missing. Therefore, the treatment outcome of the drug is hard to be determined based on the results of this study alone. Furthermore, the treatment outcome was based on retrospective analysis of data extracted from medical records, resulting in categorical data. Some objective data, such as cobblestone appearance in the nasopharynx, could not be obtained due to the retrospective study design. In the analysis of the re-occurrent patient group, it’s size (n=15) reduced its statistical value.

Despite the limitations of the study, our findings delineate the clinical aspects of CIPND and the potential efficacy of first-generation antihistamine and nasal decongestants in its treatment. Also, the study supports the establishment of CIPND as a distinct entity, advocating that this term can provide better understanding in future clinical treatment and research of the patients.