Intranasal trigeminal sensitivity: measurements before and after nasal surgery

Assessment of Intranasal Function of the Trigeminal Nerve in Daily Clinical Practice

BACKGROUND

The trigeminal nerve is a mixed cranial nerve responsible for the motor innervation of the masticatory muscles and the sensory innervation of the face, including the nasal cavities. Through its nasal innervation, we perceive sensations, such as cooling, tingling, and burning, while the trigeminal system mediates the perception of airflow. However, the intranasal trigeminal system has received little attention in the clinical evaluation of patients with nasal pathology.

SUMMARY

Testing methods that enable the clinical assessment of intranasal trigeminal function have recently been developed. This study aims to present the current clinical methods that can be utilised in everyday practice, as described in the literature. These methods include four assessment techniques: (1) the quick screening test of trigeminal sensitivity involves patients rating the intensity of ammonium vapour presented in a lipstick-like container. (2) The lateralisation test requires subjects to identify which nasal cavity is being stimulated by a trigeminal stimulus, such as eucalyptol or menthol, while the other side receives an odourless stimulus. (3) The trigeminal sticks test evaluates the trigeminal function similarly to the olfactory function using sticks filled with trigeminal stimulant liquids. (4) The automated CO2 stimulation device is used for measuring trigeminal pain thresholds, utilising intranasal CO2 stimuli to define the pain threshold.

KEY MESSAGES

Assessing intranasal trigeminal function clinically may prove useful in evaluating rhinology patients, particularly those who encounter nasal obstruction without anatomical blockage and those experiencing olfactory disorders with suspected trigeminal dysfunction. Despite their limitations, the presented methods may provide useful information about nasal patency, chemosensitivity, and pain sensation in the daily clinical practice of such patients, leading to better therapeutic decisions.

Intranasal trigeminal sensitivity to mechanical stimuli is associated with the perception of nasal patency

PURPOSE

The aim of this prospective study was to examine the characteristics of a clinical test for the assessment of nasal trigeminal sensitivity to mechanical stimuli and its association with the perception of nasal patency.

METHODS

Thirty-two normosmic healthy subjects participated (17 women and 15 men; age = 26 ± 3 years). Precisely defined air puffs were used with a flow rate of 2L/min for mechanical stimulation. They were presented to the nasal vestibule, nasal septum, and inferior turbinate with various stimulus durations. Thresholds were measured by single-staircase stimuli with changes in stimulus duration in steps of 10 ms. Trigeminal suprathreshold intensity was rated by subjects for stimulus durations of 200, 300, 400, and 500 ms. Test-retest reliability was examined by intraclass correlations (ICCs) and Bland-Altman plot with limits of agreement. Pearson's correlations were calculated between self-rated nasal patency and nasal trigeminal sensitivity.

RESULTS

As indicated by trigeminal threshold and suprathreshold intensities, the nasal vestibule is the most sensitive area among the three locations, followed by the nasal septum and the inferior turbinate (p < 0.001). Coefficients of correlations between test and retest were 0.76 for thresholds, and 0.56 suprathreshold intensities (p < 0.001). The Bland-Altman analysis showed a good agreement between test-retest values. In addition, significant positive associations between trigeminal suprathreshold intensities and self-rated nasal obstruction were found at the inferior turbinate (r = 0.4, p < 0.05).

CONCLUSION

Reliable assessment of nasal trigeminal sensitivity for air puffs appears to be possible. Nasal trigeminal suprathreshold sensitivity to mechanical stimuli is associated with the perception of nasal patency at the inferior turbinate. This opens a window into the assessment of the perception of nasal airflow in various clinical purposes, especially for patients with sinonasal diseases.

LEVEL OF EVIDENCE: 3

Unique Measurements of Intranasal Trigeminal Function: A Pilot Study

OBJECTIVE

To investigate novel methods of measuring intranasal trigeminal function and correlate to validated measures of trigeminal function.

STUDY DESIGN

Prospective cohort study.

SETTING

Tertiary medical center.

METHODS

Forty-one subjects without nasal congestion were assessed. The trigeminal temperature function of the cool/warmth detection threshold and cold/heat pain threshold was measured with the Thermal Sensory Analyzer (TSA) device, as previously validated at buccal mucosa and infraorbital skin. Identical temperature sensory function was assessed at the anterior septum and inferior turbinate. Lateralization of trigeminal odorants eucalyptol, isothiocyanate, and acetic acid was conducted. Visual analog scales (VAS) of trigeminal function were collected.

RESULTS

Extraoral cheek site and oral site thermal measures were moderately correlated, suggesting consistent assessment of trigeminal function. Nearly all intranasal thermal measures correlated between the septum and turbinate (significant correlations [ρ] ranged from .3 to .8). Oral and extraoral cheek sites had modest correlations to intranasal cold and heat pain (ρ = .4-.5). The oral site had modest correlations of cold and heat detection to intranasal sites, with turbinate appearing to have the most correlations. Isothiocyanate lateralization was the most closely correlated to intranasal thermal scores for cold and heat pain. Turbinate thermal measures had weak correlations with trigeminal VAS scores (ρ = .3-.4).

CONCLUSION

Intranasal trigeminal measures of thermal function correlate to validated extraoral and intraoral thermal measures. The turbinate appears to have stronger correlations to the septum than found in the mouth and face. TSA testing might provide a rapid, novel method of intranasal trigeminal function assessment.

Trigeminal Sensitivity in Patients With Allergic Rhinitis and Chronic Rhinosinusitis

OBJECTIVE

Allergic rhinitis (AR) and chronic rhinosinusitis with nasal polyps (CRSwNP) are of high importance in otorhinolaryngology. Some of their symptoms are related to changes in the nasal trigeminal sensitivity. The aim of this study was to compare nasal trigeminal sensitivity in patients with AR, CRSwNP, and healthy controls (HC).

METHODS

A total of 75 individuals participated (age 19-78 years; 34 AR, 10 CRSwNP and 31 HC). Olfactory function was determined using the extended Sniffin' Sticks test battery. Trigeminal sensitivity was assessed with CO₂ detection thresholds. Trigeminal negative mucosal potentials (NMP) and EEG-derived event-related potentials (ERP) were recorded in response to selective olfactory (phenylethyl alcohol) and trigeminal (CO₂ ) stimuli using high-precision air-dilution olfactometry.

RESULTS

In comparison to HC, AR patients had lower CO₂ thresholds, also reflected in shorter peak latencies in NMP and trigeminal ERP measurements. CRSwNP patients had a decreased sensitivity for trigeminal stimuli, also reflected in prolonged trigeminal ERP latencies, and reduced olfactory function compared to HC.

CONCLUSION

AR patients seemed to be more sensitive to trigeminal stimuli than CRSwNP patients. Importantly, the differences could be shown on psychophysical and electrophysiological levels. The changes in trigeminal sensitivity appear to be present already at the level of the respiratory epithelium. The differences between the two groups may depend on the specific inflammatory changes accompanying each disorder, the degree of inflammatory activity, or duration of the inflammatory disorder. However, because the sample sizes are relatively small, these results need to be confirmed in the future studies with larger groups.

LEVEL OF EVIDENCE

4 Laryngoscope, 133:654-660, 2023.

[Correlation between nasal mucosal temperature change and nasal airflow perception]

The mechanism of nasal airflow perception remains little known. It is currently believed that the main mechanism for perceiving nasal patency is to activate transient receptor potential melastatin subtype 8. Computer fluent dynamics show that increased airflow and heat flux are associated with higher subjective scores. Similarly, physical measurements of the nasal cavity using a temperature probe show a correlation between the lower nasal mucosa temperature and better results. Trigeminal function detection also indirectly confirms this. This literature review aimed to explore the role of nasal mucosal temperature change in the subjective perception of nasal patency and the secondary aim was to appraise the relevant evidence about the mechanism.

Intranasal trigeminal sensitivity may be impaired after functional nasal surgery

Functional nasal surgery is frequently performed for sinonasal diseases not responding to medical treatment. Although surgery mostly turns out to be successful in such cases, a potential side effect of manipulating the nasal mucous membrane is impairment of intranasal trigeminal function. Not well known by specialists and clinically scarcely explored, this function provides sensory information from the nasal mucosa. It is responsible for the afferent part of protective nasal reflexes such as sneezing and coughing, but also provides the feeling of nasal airflow (1). Recent work suggests that patients with low intranasal trigeminal function are more prone to suffer from nasal obstruction and may be less satisfied with functional surgery (2-6). It has been suggested that intranasal trigeminal function decreases with mucosal changes, such as chronic inflammation and improves again once the inflammation has been treated (3). However, the influence of functional nasal surgery (i.e. surgery aimed at the improvement of nasal function) with consecutive mucosal micro-injuries on intranasal trigeminal function is not yet fully clear (2-4).

Trigeminal impairment in treatment-refractory chronic nasal obstruction

BACKGROUND

Patients with anatomically unexplained, chronic nasal obstruction (CNO) that is refractory to medical treatment pose a challenge for clinicians. A surgical solution, addressing mechanical obstacles, is unsuited for these patients. CNO may result from disrupted airflow perception due to activation of the intranasal trigeminal system; therefore, aim of this study is to evaluate if intranasal trigeminal function of these CNO patients is decreased.

METHODS

In this retrospective cross-sectional study, we compared 143 CNO patients and 58 healthy volunteers, between 18 to 80 years old. We assessed nasal patency by means of rhinomanometry (RM) and measured susceptibility of intranasal trigeminal system by the trigeminal lateralization task (TLT).

RESULTS

TLT scores were significantly lower in CNO patients compared to controls (p less than 0.001), but RM scores were not different between groups. Accordingly, TLT allowed to identify CNO patients with an accuracy of the area under the curve (AUC) of 0.78, while the value for RM was at chance (AUC=0.47). CNO patients showed normal reaction to vasoconstrictive agents with significantly lower RM values after Xylomethazoline application.

CONCLUSION

Results suggest that reported nasal obstruction in CNO patients without any obvious anatomical obstacle and resistant to medical treatment may be linked to decreased perception of nasal airflow rather than physical obstruction. In this sub-set of CNO patients, trigeminal testing more adequately reflects the reported obstruction than nasal resistance assessment does. In future studies, the relation of the trigeminal status and the subjective sensation of nasal obstruction needs to be addressed with validated patient rated outcome measures (PROMs).

Some like it, some do not: behavioral responses and central processing of olfactory-trigeminal mixture perception

Exploring the potential of eucalyptol as a masking agent for aversive odors, we found that eucalyptol masks the olfactory but not the trigeminal sensation of ammonia in a previous study. Here, we further investigate the processing of a mixture consisting of eucalyptol and ammonia, two olfactory–trigeminal stimuli. We presented the two pure odors and a mixture thereof to 33 healthy participants. The nostrils were stimulated alternately (monorhinal application). We analyzed the behavioral ratings (intensity and pleasantness) and functional brain images. First, we replicated our previous finding that, within the mixture, the eucalyptol component suppressed the olfactory intensity of the ammonia component. Second, mixture pleasantness was rated differently by participants depending on which component dominated their mixture perception. Approximately half of the volunteers rated the eucalyptol component as more intense and evaluated the mixture as pleasant (pleasant group). The other half rated the ammonia component as more intense and evaluated the mixture as unpleasant (unpleasant group). Third, these individual differences were also found in functional imaging data. Contrasting the mixture either to eucalyptol or to both single odors, neural activation was found in the unpleasant group only. Activation in the anterior insula and SII was interpreted as evidence for an attentional shift towards the potentially threatening mixture component ammonia and for trigeminal enhancement. In addition to insula and SII, further regions of the pain matrix were involved when assessing all participant responses to the mixture. Both a painful sensation and an attentional shift towards the unpleasant mixture component complicates the development of an efficient mask because a pleasant perception is an important requirement for malodor coverage.

[Breath changes induced by short chemosensory stimuli cannot be intentionally suppressed]

INTRODUCTION

Breathing changes induced by repeated short olfactory stimuli are used as an objective indicator of the integrity of the olfactory system. Until now, it has not been investigated whether chemosensorically induced changes in inspiratory and expiratory time parameters can be suppressed intentionally. The same applies to breathing changes due to weak CO₂ stimuli.

METHODOLOGY

34 healthy adult normosmics were stimulated during relaxed regular nasal breathing using a flow olfactometer with nine differently concentrated H₂S and three weak CO₂ stimulation pulses. They were instructed to intentionally maintain regular nasal breathing during the stimulation. A significant breathing change was present if the duration of the inspiration (DIN) or the expiration (DEX) of the first stimulatory breath was outside the double standard deviation of the mean of five prestimulatory regular breaths. These could be shortened or extended the DIN or DEX.

RESULTS

Despite high motivation, the chemosensorically induced breathing changes could not be suppressed intentionally. Rest breathing reacted to both stimulants by changes in both the inspiratory and the expiratory time parameters. However, it outweighed the expiratory reactions. CO₂ evoked more breathing changes than H₂S. The frequency of reaction rate of H₂S stimuli was not concentration-dependent. Strong H₂S stimuli induced more frequent shortening than prolongation of DEX.

CONCLUSIONS

Chemosensorically triggered breathing changes cannot be suppressed intentionally. They therefore provide an additional objective tool to check the functionality of nasal chemosensory afferents.

The intranasal trigeminal system

Many odors activate the intranasal chemosensory trigeminal system where they produce cooling and other somatic sensations such as tingling, burning, or stinging. Specific trigeminal receptors are involved in the mediation of these sensations. Importantly, the trigeminal system also mediates sensitivity to airflow. The intranasal trigeminal and the olfactory system are closely connected. With regard to central nervous processing, it is most interesting that trigeminal stimuli can activate the piriform cortex, which is typically viewed as the primary olfactory cortex. This suggests that interactions between the two systems may form at a relatively early stage of processing. For example, there is evidence showing that acquired olfactory loss leads to reduced trigeminal sensitivity, probably on account of the lack of interaction in the central nervous system. Decreased trigeminal sensitivity may also be responsible for changes in airflow perception, leading to the impression of congested nasal airways.

Axonal Guidance Signaling Pathway Is Suppressed in Human Nasal Polyps

Background Dysfunctional innervation might contribute to the pathogenesis of chronic rhinosinusitis with nasal polyps (CRSwNP), but the state of the axonal outgrowth signaling in CRSwNP is unknown. The purpose of this study was to explore the axonal outgrowth pathway-related protein expression in CRSwNP. Methods Institutional review board approved study in which tissue proteomes were compared between control and CRSwNP patients (n = 10/group) using an aptamer-based proteomic array and confirmed by whole transcriptomic analysis. Results Compared with controls, proteins associated with axonal guidance signaling pathway such as beta-nerve growth factor, semaphorin 3A, Ras-related C3 botulinum toxin substrate 1, Bcl-2, protein kinase C delta type, and Fyn were significantly decreased in patients with CRSwNP (fold change [FC] = -1.17, P = .002; FC = -1.09, P < .001; FC = -1.33, P < .001; FC = -1.31, P < .001; FC = -1.31, P = .004; and FC = -1.20, P = 0.012, respectively). In contrast, reticulon-4 receptor, an inhibitory factor, was significantly increased in patients with CRSwNP (FC = 1.25, P < .001). Furthermore, neuronal growth-associated proteins such as ciliary neurotrophic factor receptor subunit alpha, neuronal growth regulator 1, neuronal cell adhesion molecule, neural cell adhesion molecule L1, platelet-derived growth factor subunit A, and netrin-4 were all significantly decreased in patients with CRSwNP (FC = -1.25, P < .001; FC = -1.27, P = .002; FC = -1.65, P = .013; FC = -4.20, P < .001; FC = -1.28, P < .001; and FC = -2.31, P < .001, respectively). In contrast, tissue eosinophil count ( P < .001) and allergic inflammation factors such as IgE, periostin, and galectin-10 were all significantly increased in patients with CRSwNP (FC = 12.28, P < .001; FC = 3.95, P < .001; and FC = 2.44, P < .001, respectively). Furthermore, the log FC of the studied proteins expression significantly and positively correlated with log FC of their mRNA expression ( P < .001, r = .88). Conclusions Axonal guidance signaling and neural growth factors pathways proteins are significantly suppressed in eosinophilic CRSwNP.

Effects of "trigeminal training" on trigeminal sensitivity and self-rated nasal patency

Purpose

Patients with the feeling of a congested nose not always suffer from an anatomical obstruction but might just have a low trigeminal sensibility, which prevents them from perceiving the nasal airstream. We examined whether intermittent trigeminal stimulation increases sensitivity of the nasal trigeminal nerve and whether this effect is accompanied by subjective improvement of nasal breathing.

Method

Thirty-five patients (M_age = 58.4 years; SD = 14.8; Min_age = 21 years; Max_age = 79 years; 43% females) and 30 healthy controls (M_age = 36.7 years, SD = 14.5; Min_age = 20 years; Max_age = 73 years; 60% females) participated in a study comprised of two sessions separated by “trigeminal training”. During each session, trigeminal sensitivity towards CO₂, trigeminal lateralization abilities and ratings of nasal patency were assessed. Age and training compliance were controlled.

Results

“Trigeminal training” had a positive effect on trigeminal sensitivity in both groups, (p = .027) and this effect depended on the training compliance (p < .001). “Trigeminal training” had no effect on lateralization abilities of the subjects (p > .05). Ratings of nasal patency increased in patients (p = .03), but not in controls.

Conclusions

“Trigeminal training” consisting of intermittent presentation of diverse stimulants leads to an increase of trigeminal sensitivity, but this effect depended on the training compliance. Importantly, in patients, this training is also associated with an increase in self-rated nasal patency.

Intranasal trigeminal function in patients with empty nose syndrome

OBJECTIVES/HYPOTHESIS

Trigeminal nerve mediates the perception of nasal airflow. This study examines whether impaired intranasal trigeminal function is a part of the paradoxical nasal obstruction sensation in patients with empty nose syndrome (ENS).

STUDY DESIGN

Prospective case-control study in a tertiary hospital.

METHODS

Three groups were examined: 1) ENS patients with previous bilateral near total inferior turbinectomy, 2) patients who underwent near total inferior turbinate removal (ITR) without ENS symptoms, and 3) control participants. All participants examined with active anterior rhinomanometry, olfactory testing (extended Sniffin' Sticks test), and trigeminal testing (lateralization task using menthol and odorless solvent).

RESULTS

Seventy-one participants were included (21 ENS patients, 18 ITR patients, and 31 controls). Analyses revealed that ENS patients had significantly lower scores on trigeminal lateralization testing than the ITR group and controls. The ENS group had also significantly lower scores in olfactory testing than controls. No statistical differences were found in rhinomanometry between groups. The gender factor was not associated with the chemosensory testing; however, this was not the case with the age factor, as trigeminal test results were negatively correlated.

CONCLUSIONS

This study demonstrates significantly impaired intranasal trigeminal function in ENS patients when compared with ITR patients and controls. Further prospective studies are needed to clarify the role of preoperative trigeminal function of these patients and the contribution of surgery to this impairment.

LEVEL OF EVIDENCE

3b. Laryngoscope, 127:1263-1267, 2017.

Subjective changes in nasal patency after chewing a menthol-containing gum in patients with olfactory loss

CONCLUSION

The subjective increase in nasal patency after oral menthol application depends on olfactory function. In patients with relatively low olfactory sensitivity, this effect is small or absent. It was hypothesized that this may also modulate the sensation of nasal blockage.

OBJECTIVE

Menthol stimulates the nasal trigeminal nerve, resulting in a subjectively increased nasal airflow and patency without objectively measurable changes. Patients suffering from olfactory impairment also express a reduced nasal trigeminal sensitivity. The aim of this investigation was to examine the effect of menthol on nasal patency ratings in a group of patients suffering from olfactory dysfunction.

METHODS

A group of 92 patients with olfactory impairment was included in this study. Olfactory function was assessed using the 'Sniffin' Sticks.' Patients were instructed to chew a menthol-containing gum for 30 s, after which they rated the change in nasal patency on a categorical scale.

RESULTS

Patients who rated the change in nasal patency as pronounced scored higher on the Sniffin' Sticks olfactory test compared to patients who experienced little or no change in nasal patency after chewing the menthol-containing gum. On average, similar changes could be observed for all etiologies of olfactory impairment included in this study.