Office Procedures for Quantitative Assessment of Olfactory Function

Olfaction in dentistry

Practitioners of oral medicine frequently encounter patients with complaints of taste disturbance. While some such complaints represent pathological processes specific to the gustatory system, per se, this is rarely the case. Unless taste-bud mediated qualities such as sweet, sour, bitter, salty, umami, chalky, or metallic are involved, 'taste' dysfunction inevitably reflects damage to the sense of smell. Such 'taste' sensations as chicken, chocolate, coffee, raspberry, steak sauce, pizza, and hamburger are dependent upon stimulation of the olfactory receptors via the nasopharynx during deglutition. In this paper, we briefly review the anatomy, physiology, and pathophysiology of the olfactory system, along with means for clinically assessing its function. The prevalence, etiology, and nature of olfactory disorders commonly encountered in the dental clinic are addressed, along with approaches to therapy and patient management.

Grafting the olfactory epithelium to the olfactory bulb

BACKGROUND

Impaired olfactory function leads to a decrease in the quality of life for many patients. Surgical treatment options are limited, especially for those suffering from hyposmia or anosmia after posttraumatic injury to the olfactory nerves. Stem cells located in the olfactory epithelium (OE) have the capacity to grow new neurons, making the OE an ideal candidate for restorative tissue grafting. This study was performed to determine if strips of OE survive transplantation directly to the olfactory bulb (OB).

METHODS

Transgenic mice, expressing a green fluorescent protein (GFP), were used to obtain the donor graft tissue. Strips of OE from GFP donor mice were transplanted directly to sites in the OB and cerebral cortex (CC; control sites) of wild-type mice. Graft survival rates at 30 days were determined for transplant sites in the OB and CC.

RESULTS

Strips of OE from transgenic mice survived transplantation to the OB and continued to express the GFP marker protein. The 30-day survival rate in the OB (83%, 5 of 6 grafts) was the same as in the CC (10 of 12 grafts). The morphology of the graft revealed characteristics found in normal OE.

CONCLUSION

We showed that strips of OE can be successfully grafted to both the OB and CC. Grafts of the OE, if strategically positioned on the ventral surface of the bulb and given access to the nasal cavity, could provide the basis for new surgical treatments to restore olfactory function.

Allergic rhinitis and aspirin-exacerbated respiratory disease as predictors of the olfactory outcome after endoscopic sinus surgery

BACKGROUND

Unlike the functional outcomes of endoscopic sinus surgery, which have been thoroughly studied, the effect of the surgery on olfactory performance and the relative predictive factors have not been adequately assessed by literature. Allergic rhinitis and aspirin-exacerbated respiratory disease (AERD) are examined as potential confounding factors of the olfactory outcome in patients with extensive nasal polyposis and rhinosinusitis treated with functional endoscopic sinus surgery (FESS).

METHODS

A population of 116 adults with severe nasal polyposis was subjected to FESS after failure of the appropriate medical treatment. The olfactory outcome was quantified by Sniffin' Sticks at the 1st, 3rd, and 6th postoperative month in relation to the concomitant presence of allergic rhinitis (n = 62) or AERD (n = 18).

RESULTS

Allergic patients seemed to perform worse than nonallergic patients at all time frames. However, when patients with similar olfactory acuity, age, and medical history are compared, allergic rhinitis does not seem to affect the postoperative improvement of the composite threshold-discrimination-identification scores. The same seems to apply for the likelihood of acquiring normosmia after surgery. On the contrary, AERD significantly limits the recovery of olfactory function at all follow-up examinations and patients with AERD are unlikely to become normosmic.

CONCLUSION

The olfactory recovery after FESS for nasal polyposis is significantly affected by the concomitant presence of AERD. Although allergy seems to have a general negative effect on olfactory acuity, it was not found to affect the extent of the olfactory improvement, when patients with comparable preoperative characteristics are addressed.

Olfactory function and disease severity in chronic rhinosinusitis

BACKGROUND

Olfactory dysfunction is deemed to be a significant contributor to poor quality of life (QOL). However, little is known about the relationship of olfactory testing to other measures of disease burden in patients with chronic rhinosinusitis (CRS). In this study, we examine the relationship of olfactory function to computed tomography (CT) scores, endoscopy scores, and QOL measures in patients with CRS.

METHODS

A multi-institutional, cross-sectional analysis of 367 patients was performed. Several objective measures were collected: the Smell Identification Test, Lund-MacKay CT score, Lund-Kennedy endoscopy score, two validated disease-specific QOL instruments, the Rhinosinusitis Disability Index and the Chronic Sinusitis Survey, and a general health-related QOL instrument, the Medical Short Form-36. Analysis of variance was performed. Correlation coefficients were calculated.

RESULTS

Patients with olfactory dysfunction had significantly worse mean endoscopy scores (normosmics, 4.16 [+/- 3.97]; hyposmics, 6.26 [+/- 4.21]; anosmics, 9.61 [+/- 4.48]; p < 0.001) and significantly worse CT scores (normosmics, 9.11 [+/- 5.40]; hyposmics, 11.16 [+/- 5.96]; anosmics, 17.62 [+/- 5.37]; p < 0.001). Endoscopy scores were moderately correlated with olfactory scores (r = -0.46; 95% CI, -0.38, -0.54; p < 0.001). CT scores were moderately correlated with olfactory scores (r = -0.53; 95% CI, -0.45, -0.60; p < 0.001). Olfactory function was not correlated with disease-specific or general health-related QOL measures.

CONCLUSION

Although previous studies have suggested that olfactory impairment is associated with poor QOL, this study found no such correlation. In contrast, olfaction scores correlated well with other objective measures of CRS, namely, endoscopy and CT scores.

Preoperative prognostic factors for olfactory change after functional endoscopic sinus surgery

BACKGROUND

Functional endoscopic sinus surgery (FESS) has been considered to improve the olfactory function in patients with chronic rhinosinusitis. However, which factors might affect the olfactory outcome after FESS has not been well investigated.

METHODS

A total of 70 patients with chronic rhinosinusitis who underwent FESS were enrolled in the study. The potential prognostic factors for improvement in olfaction after FESS were evaluated in these patients. On the day before FESS, the olfactory function was evaluated by a symptom score, a phenyl ethyl alcohol odor detection threshold test, the University of Pennsylvania Smell Identification Test, and a short-term odor memory/discrimination test, and were reevaluated by the same methods 6 months after FESS.

RESULTS

The degree of nasal obstruction, the second minimal cross-sectional area measured by acoustic rhinometry, computed tomography scores before FESS, the degree of preoperative olfactory loss indicated by threshold and identification scores, and coexistence of nasal polyps or allergic rhinitis were not significantly reliable to influence the rates of olfactory improvement after FESS.

CONCLUSION

Degree of nasal obstruction, extent of rhinosinusitis disease, and coexistence of nasal polyps or allergic rhinitis did not predicate the overall possibility of any olfactory improvement after FESS.

Olfactory bulb volume in patients with sinonasal disease

BACKGROUND

The aim of this study was to assess the volume of the olfactory bulb (OB) in patients with chronic rhinosinusitis (without nasal polyposis at the endoscopic evaluation) and to evaluate the correlation between this measure and the degree of sinonasal inflammation.

METHODS

Patients with sinonasal disease (SND; n = 22) were compared with healthy controls (n = 16) using orthonasal and retronasal olfactory test results and OB volumes measurement calculated by planimetric manual contouring using standardized methods. The Lund-Mackay score (originally described for CT scan) was also used to gauge sinonasal inflammation (SND score).

RESULTS

The two groups were not significantly different in terms of age or distribution of sex. Patients had significantly higher right- and left-sided SND scores than controls. There was no significant group difference between patients and controls with regard to OB volume. However, patients with an SND score < or =12 had larger OB volumes than patients with higher SND scores (p < 0.001). Even when controlling for the subjects' age, a significant correlation was present between OB volume and SND score (r = -0.52; p = 0.001) with smaller OB volumes being associated with a higher degree of sinonasal pathology.

CONCLUSION

OB volume correlated with the SND score, which is an indicator of the degree of sinonasal inflammation. SND patients with a slight decrease or even normal olfactory function may already exhibit changes in their OB volume. This study also seems to emphasize the idea that OB volume changes are more sensitive to subtle changes in the olfactory system than results from psychophysical testing.

Olfactory function in patients with chronic rhinosinusitis before and after functional endoscopic sinus surgery

BACKGROUND

The olfactory loss in patients with chronic rhinosinusitis has been measured by different methods. However, the results have been variable and it is not clear whether functional endoscopic sinus surgery (FESS) significantly improves olfactory function. This study was performed to evaluate the influences of FESS on olfactory function in patients with chronic rhinosinusitis using three different types of olfactory tests.

METHODS

Seventy patients with chronic rhinosinusitis were administered the University of Pennsylvania Smell Identification Test (UPSIT), a single staircase phenyl ethyl alcohol odor detection threshold test (STT), and a short-term odor memory/discrimination test a day before and 6 months after FESS. A questionnaire inquiring about the patients' self-perception of olfactory function was administered also. Independent ratings of the severity of chronic rhinosinusitis before FESS were established from CT scans.

RESULTS

Fifty-two (74.3%) of the patients reported that their olfactory function was impaired before surgery, and 68.6% of the patients reported impaired olfactory function after surgery, a difference that was not significant. No meaningful changes in any of the olfactory test scores were noted 6 or more months after FESS. Preoperatively, small correlations between CT scores and the symptom scores (r = 0.278; p = 0.024), threshold scores (r = -0.27; p = 0.031), and UPSIT scores (r = -0.36; p = 0.003) were observed.

CONCLUSION

In patients with severe rhinosinusitis, FESS had little impact on the ability to smell, regardless of the method for assessing smell function. Subtle associations between olfactory function and the severity of chronic rhinosinusitis determined by CT were observed, however, preoperatively. The olfactory test measures were correlated with one another both pre- and postoperatively.

Olfactory dysfunction in patients with narcolepsy with cataplexy is restored by intranasal Orexin A (Hypocretin-1)

Until recently, olfactory dysfunction was an unknown feature of narcolepsy. Orexin A, also called hypocretin-1, is abnormally decreased or undetectable in the cerebrospinal fluid of narcoleptic patients with cataplexies. As hypothalamic orexin-containing neurons project throughout the entire olfactory pathway, from the olfactory mucosa to the olfactory cortex, disturbed orexinergic transmission may crucially be involved in impaired olfactory performance of narcolepsy patients. In our study we analysed the olfactory performance (threshold, discrimination, identification and sum score of these measurements, the TDI score) of narcoleptic patients with cataplexies (n = 10) and of age-, gender-, BMI- and smoker/non-smoker-matched healthy controls (n = 10). We then in a double-blind, randomized, placebo-controlled cross-over design applied orexin A intranasally to seven of the patients and measured 2-phenyl-ethyl alcohol (PEA) single-staircase odour detection thresholds. Compared to the controls, patients showed significantly lower scores for olfactory threshold (patients: median 8.0, range 4.0-10.5; controls: median 9.4, range 7.5-13.3; P < 0.05), discrimination (patients: median 12.5, range 10-15; controls: median 15.0, range 12-16; P < 0.005), identification (patients: median 13.0, range 10-16; controls: median 14.0, range 13-16; P < 0.05) and TDI score (patients: median 33.4, range 30-36; controls: median 38.4, range 35-43; P < 0.0001). In all patients, the PEA olfactory threshold score increased after administration of orexin A (median 11.5, range 6.5-13.25) compared to placebo (median 7.75, range 6.25-11.25; P < 0.05). Our results support the hypothesis that mild olfactory dysfunction is an intrinsic symptom of narcolepsy with cataplexies. The observation that intranasal orexin A restores olfactory function is in favour of this hypothesis. Furthermore, our data support that the pathophysiological mechanism underlying olfactory dysfunction in narcolepsy is the lack of CNS orexin.

Drug-induced taste disorders

Numerous drugs have the potential to adversely influence a patient's sense of taste, either by decreasing function or producing perceptual distortions or phantom tastes. In some cases, such adverse effects are long lasting and cannot be quickly reversed by drug cessation. In a number of cases, taste-related adverse effects significantly alter the patient's quality of life, dietary choices, emotional state and compliance with medication regimens. In this review, we describe common drug-related taste disturbances and review the major classes of medications associated with them, including antihypertensives, antimicrobials and antidepressants. We point out that there is a dearth of scientific information related to this problem, limiting our understanding of the true nature, incidence and prevalence of drug-related chemosensory disturbances. The limited data available suggest that large differences exist among individuals in terms of their susceptibility to taste-related adverse effects, and that sex, age, body mass and genetic variations in taste sensitivity are likely involved. Aside from altering drug usage, management strategies for patients with taste-related adverse effects are sorely needed. Unfortunately, stopping a medication is not always an easy option, particularly when one is dealing with life-threatening conditions such as seizures, cancer, infection, diabetes mellitus and uncontrolled hypertension. Hopefully, the information contained in this review will sensitize physicians, researchers and drug manufacturers to this problem and will result in much more research on this pressing topic.