Management of long-lasting phantosmia: a systematic review

Olfactory Nomenclature: An Orchestrated Effort to Clarify Terms and Definitions of Dysosmia, Anosmia, Hyposmia, Normosmia, Hyperosmia, Olfactory Intolerance, Parosmia, and Phantosmia/Olfactory Hallucination

BACKGROUND

Definitions are essential for effective communication and discourse, particularly in science. They allow the shared understanding of a thought or idea, generalization of knowledge, and comparison across scientific investigation. The current terms describing olfactory dysfunction are vague and overlapping.

SUMMARY

As a group of clinical olfactory researchers, we propose the standardization of the terms "dysosmia," "anosmia," "hyposmia," "normosmia," "hyperosmia," "olfactory intolerance," "parosmia," and "phantosmia" (or "olfactory hallucination") in olfaction-related communication, with specific definitions in this text.

KEY MESSAGES

The words included in this paper were determined as those which are most frequently used in the context of olfactory function and dysfunction, in both clinical and research settings. Despite widespread use in publications, however, there still exists some disagreement in the literature regarding the definitions of terms related to olfaction. Multiple overlapping and imprecise terms that are currently in use are confusing and hinder clarity and universal understanding of these concepts. There is a pressing need to have a unified agreement on the definitions of these olfactory terms by researchers working in the field of chemosensory sciences. With the increased interest in olfaction, precise use of these terms will improve the ability to integrate and advance knowledge in this field.

Novel Therapies in Olfactory Disorders

Purpose of Review

To summarize and critically review the recent literature on novel treatments for olfactory disorders (OD).

Recent Findings

Emerging therapies in the management of OD include multiple vitamins and supplements, biologics, neuromodulators, and intranasal agents. There is also an active investigation into treatments that harness the neuroregenerative properties of the olfactory epithelium, such as platelet-rich plasma and stem cell transplantation.

Summary

Successful management of OD is multimodal and tailored to the underlying etiology. As the findings of further investigations accrue, the management of OD will undoubtedly continue to be advanced and refined, and likely harness the intrinsic neuroregenerative properties of the olfactory system.

Phantom smells: a prevalent COVID-19 symptom that progressively sets in

PURPOSE

One of the long-term symptoms of COVID-19 is phantosmia, a type of Olfactory Disorder (OD) that has deleterious impacts on patients' quality of life. The aim of this article was to study how this poorly understood qualitative OD manifests itself in the COVID-19.

METHODS

4691 patients with COVID-19 responded to our online questionnaire focusing on COVID-19-related OD. We first analyzed the prevalence of phantosmia in this population. Then, with the help of Natural Language Processing techniques, we investigated the qualitative descriptions of phantom smells by the 1723 respondents who reported phantosmia.

RESULTS

The prevalence of phantosmia was of 37%. Women were more likely to report phantosmia than men, as well as respondents for whom OD was described as fluctuating rather than permanent, lasted longer, was partial rather than total and appeared progressively rather than suddenly. The relationship between OD duration and phantosmia followed a logarithmic function, with a prevalence of phantosmia increasing strongly during the first 2 months of the disease before reaching a plateau and no decrease over the 15 months considered in this study. Qualitative analyses of phantosmia descriptions with a sentiment analysis revealed that the descriptions were negatively valenced for 78% of the respondents. Reference to "tobacco" was more frequent in non-smokers. Source names and odor characteristics were used differently according to age and OD duration.

CONCLUSION

The results of this descriptive study of phantosmia contribute to the current efforts of the medical community to better understand and treat this rapidly increasing COVID-19-related OD.

International consensus statement on allergy and rhinology: Olfaction

BACKGROUND

The literature regarding clinical olfaction, olfactory loss, and olfactory dysfunction has expanded rapidly over the past two decades, with an exponential rise in the past year. There is substantial variability in the quality of this literature and a need to consolidate and critically review the evidence. It is with that aim that we have gathered experts from around the world to produce this International Consensus on Allergy and Rhinology: Olfaction (ICAR:O).

METHODS

Using previously described methodology, specific topics were developed relating to olfaction. Each topic was assigned a literature review, evidence-based review, or evidence-based review with recommendations format as dictated by available evidence and scope within the ICAR:O document. Following iterative reviews of each topic, the ICAR:O document was integrated and reviewed by all authors for final consensus.

RESULTS

The ICAR:O document reviews nearly 100 separate topics within the realm of olfaction, including diagnosis, epidemiology, disease burden, diagnosis, testing, etiology, treatment, and associated pathologies.

CONCLUSION

This critical review of the existing clinical olfaction literature provides much needed insight and clarity into the evaluation, diagnosis, and treatment of patients with olfactory dysfunction, while also clearly delineating gaps in our knowledge and evidence base that we should investigate further.

Short duration phantosmia changes in a post‐COVID‐19 patient in Bangladesh

Phantosmia is a condition in perceived odors that do not exist. Given the high outlook and swift recovery of COVID‐19‐induced olfactory dysfunction, the emphasis should be on patients presenting with a poor prognosis who might receive from early management to avoid sequelae such as olfactory dysfunction‐related phantosmia.

Phantosmia Among Pediatric, Adolescent, and Young Adult Patients Receiving Proton Beam Therapy

Purpose

Phantosmia, an underreported toxicity of brain radiation therapy (RT), is defined as an olfactory disorder resulting in a malodorous phantom smell. This study aimed to characterize the incidence of phantosmia in patients treated with intensity modulated proton therapy (IMPT).

Methods and Materials

In this institutional review board–approved retrospective study, the electronic medical record of a pencil beam scanning-only proton center was queried for patients ≤39 years of age who received IMPT for primary intracranial, metastatic intracranial, skull base, nasopharyngeal or sinonasal neoplasms between August 2019 and December 2020. Patient, clinical, and phantosmia-related characteristics were collected. The olfactory region was defined to include the olfactory bulb and tract. Phantosmia severity was graded by intervention use (mild, no intervention; moderate, supportive treatment; severe, RT discontinuation).

Results

Ninety-nine patients met the inclusion criteria. Twelve patients (12.1%) reported phantosmia. Patients described perceiving a “chlorine,” “broccoli,” “stale water,” “metallic,” or “noxious” smell. Of the patients who reported phantosmia, median age was 17 (12-33) years, 66.7% were male, and 91.7% had intracranial tumors. None of the patients had prior RT. Chemoradiotherapy treatment did not correlate with phantosmia development (odds ratio, 1.09; 95% confidence interval, 0.32-3.70; P = .90). Ten patients experienced accompanying toxicities, including taste changes (n = 3), vision disturbances (n = 5), and nausea/emesis (n = 7). Phantosmia was mild (n = 7) or moderate (n = 5). All patients completed their RT course. Sixty-seven percent received craniospinal irradiation (CSI) while 33% received focal brain RT, with the olfactory region receiving doses as low as 0.5 Gy. Notably, 8 of 27 patients who received CSI (30%) reported phantosmia (odds ratio, 7.66; 95% confidence interval, 2.07-28.34; P = .002).

Conclusions

In the first-ever study examining radiation-induced phantosmia among children and young adults treated with IMPT, all affected patients received irradiation dose to the olfactory region. Physician awareness of phantosmia, especially in the context of CSI, may improve the patient experience and treatment compliance. A prospective study is needed to elucidate frequency, severity, and phantosmia mechanism.

Olfactory hallucinations in a population-based sample

Olfactory hallucinations referring to olfactory perceptions in the absence of chemical stimuli, occur in non-clinical and clinical populations. Few studies have investigated their prevalence in the general population and little is known about factors triggering and maintaining them such as substance use, severe life events, and mood. We analyzed self-report data from 2500 community dwelling Norwegians, aged 18-96 years, for occurrence of olfactory hallucinations and co-occurring hallucinations in other modalities (auditory, visual, tactile). Analyses included age, sex, self-reported symptoms of depression and anxiety, mental health status, and experience of severe life-events. The results show that 4.2% (95% CI 3.5-5.1%) reported having experienced olfactory hallucinations, and 56% of individuals experiencing olfactory hallucinations also reported these in combination with hallucinations in other modalities. Prevalence varied significantly in terms of age and sex, in that olfactory hallucinations were most frequently reported by young individuals and females. Self-reported symptoms of anxiety and experience of stressful life events were significantly associated with olfactory hallucinations, suggesting that experiencing olfactory hallucinations may negatively affect functioning and may increase the likelihood of developing psychopathology. Findings underline the need to continue to examine olfactory hallucinations albeit with a more comprehensive assessment in order to increase knowledge on this experience.

Qualitative Olfactory Disorders: Patient Experiences and Self-Management

Background

Qualitative olfactory disorders in the form of parosmia and phantosmia are very subjective and cannot be measured at present. They pose an unpleasant experience for patients and a therapeutic challenge for clinicians.

Objective

This study aimed to characterise the specific experiences of patients affected by the qualitative symptoms of parosmia and phantosmia including both triggers for symptoms and self-help measures they have tried.

Methods

A cross-sectional survey questionnaire was developed with the input of patient experts within the charity Fifth Sense. The survey was then open online for 3 months to charity members complaining of qualitative symptoms. The survey captured the frequency and impact of symptoms and self-management undertaken. Reflective feedback was also captured from a patient workshop.

Results

There were 100 participants; 61% female, age range 13-88. Common self-reported aetiology included sinonasal disease (17%), idiopathic (33%) and post-viral olfactory loss (26%) and post-traumatic olfactory loss (23%). Parosmia was reported as a daily symptom in 67% compared to 31% for phantosmia; 36% complained of suffering with both symptoms. Only 4% of respondents reported having received any successful treatment for their qualitative symptoms and 58% reported having received no treatment whatsoever. Olfactory training was the most common self-management method reported.

Conclusion

This study illustrates that qualitative disturbances remain problematic for those who experience them due to the duration of symptoms, the relative lack of experience or knowledge amongst medical professionals and the lack of therapeutic options. In future, consideration needs to be given to adaptation and coping strategies to help patients deal with these symptoms.

Phantosmia with COVID-19 Related Olfactory Dysfunction: Report of Nine Case

Phantosmia has been described as a sense of smell without a true stimulating odor and not been reported with COVID-19 disease. Nine patients admitted to Ear Nose Throat (ENT) Clinic with complaints of a phantom smell sense after an average of 33.5 ± 9.5 days after the initial PCR diagnosis. According to the Sniffin 'Sticks test, phantosmia was associated with objective hyposmia in three patients with the persistent phantom smell, and other six patients were detected normosmic. Phantosmia or olfactory hallucinations have not been previously associated with COVID-19 disease. Additionally, COVID-19 related phantosmia showed different characteristics according to described in the literature.

Intranasal sodium citrate in quantitative and qualitative olfactory dysfunction: results from a prospective, controlled trial of prolonged use in 60 patients

Objectives

We have previously shown that treatment with intranasal sodium citrate may be beneficial in post-infectious olfactory dysfunction. Sodium citrate reduces free intranasal calcium and is, therefore, thought to prevent calcium-mediated feedback inhibition at the level of the olfactory receptor. We aimed to determine whether treatment with a 2-week course of intranasal sodium citrate improves quantitative olfactory function in patients with post-infectious impairment. We also aimed to determine whether sodium citrate is beneficial in treating qualitative olfactory dysfunction.

Methods

We performed a prospective, controlled study. Patients applied intranasal sodium citrate solution to the right nasal cavity for 2 weeks. The left nasal cavity was untreated and, therefore, acted as an internal control. Monorhinal olfactory function was assessed using the “Sniffin’ Sticks” composite ‘TDI’ score, before and after treatment. The presence of parosmia and phantosmia was also assessed.

Results

Overall, there was a significant increase in TDI after treatment (using the best of right and left sides). Treatment with sodium citrate did not significantly improve quantitative olfactory function, compared to control. The proportion of patients reporting parosmia did not change significantly after treatment. However, there was a significant reduction in the proportion of patients reporting phantosmia, at the end of the study period.

Conclusions

Treatment with intranasal sodium citrate for a period of 2 weeks does not appear to improve quantitative olfactory function in patients with post-infectious impairment, compared to control. It may, however, be beneficial in treating phantosmia, which should be further addressed in future work.

Prescription Medication Use and Phantom Odor Perception Among US Adults

INTRODUCTION

Prescription medication use may be associated with phantom odor perception. We evaluated associations between number of prescription medications and their therapeutic class and phantom odor perception among U.S. adults.

METHODS

Data were collected between 2011-2014 as part of the National Health and Nutrition Examination Survey (NHANES). A complex sampling design resulted in a nationally representative sample of 7,417 adults aged 40 years and older. During an in-home interview, participants were asked whether they had experienced an unpleasant, bad, or burning odor when nothing is there. Prescription medication use was assessed using validation with prescription bottles, when possible.

RESULTS

Almost one quarter (23.3%) of adults uses ≥5 prescription medications. Use of five or more prescription medications is associated with 70% greater odds of phantom odor perception (OR 1.69 (1.09, 2.63)). Among adults 60 years and older, antidiabetic medications, antihyperlipidemic agents, and proton pump inhibitors are associated with 74-88% greater odds of report of phantom odor [OR=1.74 (1.09, 2.77), OR=1.85 (1.22. 2.80), and OR=1.88 (1.15, 3.07)], respectively.

CONCLUSIONS

Phantom odor perception may be a side effect of antidiabetic or antihyperlipidemic agents. Among people taking proton pump inhibitors, phantom odors may also be a consequence of gastric gas reflux.

IMPLICATIONS

Common prescription medications may be providing an olfactory stimulus.

Propofol Total Intravenous Anesthesia as an Intervention for Severe Radiation-Induced Phantosmia in an Adolescent with Ependymoma

Radiation-induced phantosmia has been reported both in children and adults. A fraction of these patients have nausea and vomiting triggered by phantosmia. Radiation-induced phantosmia, although transient, can be distressing enough to prevent a patient from staying still during radiation therapy. To date, specific interventions for radiation-induced phantosmia, including anesthesia, have not been reported. We report for the first time anesthesia as an intervention for transient severe radiation-induced phantosmia, in a 16-year-old girl with ependymoma undergoing proton therapy, and we discuss the pros and cons of techniques for anesthesia and airway management.