To evaluate the functional magnetic resonance imaging changes in the olfactory structures of coronavirus disease 2019 patients experiencing olfactory dysfunction.

This study included patients aged 25–65 years who presented with a sudden loss of smell, confirmed coronavirus disease 2019 infection, and persistent olfactory dysfunction for a minimum of 2 months without any treatment.

Irrespective of the side of brain activation, the analysis of the cumulative maximum diameter of the activation zones revealed significantly lower activation in the upper frontal lobe (p = 0.037) and basal ganglia (p = 0.023) in olfactory dysfunction patients. Irrespective of the side of activation, the analysis of the number of activation points demonstrated significantly lower activation in the upper frontal lobe (p = 0.036) and basal ganglia (p = 0.009) in olfactory dysfunction patients.

Patients with coronavirus-triggered olfactory dysfunction exhibited lower activity in their basal ganglia and upper frontal lobe.

Olfaction has recently found clinical value in prediction, discrimination and prognosis of some neurodegenerative disorders. However, data originating from standard tests on olfactory dysfunction in Huntington's disease are limited to odour identification, which is only one domain of olfactory perceptual space.

Twenty-five patients and 25 age- and gender-matched controls were evaluated by the Sniffin’ Sticks test in three domains of odour threshold, odour discrimination, odour identification and the sum score of them. Patients’ motor function was assessed based on the Unified Huntington's Disease Rating Scale.

Compared with controls, patients’ scores of all olfactory domains and their sum were significantly lower. Besides, our patients’ odour threshold and odour discrimination impairments were more frequently impaired than odour identification impairment (86 per cent and 81 per cent vs 34 per cent, respectively).

Olfactory impairment is a common finding in patients with Huntington's disease; it is not limited to odour identification but is more pronounced in odour discrimination and odour threshold.

The aim of this study was to identify the potential electrophysiological biomarkers of human responses by comparing the electroencephalogram brain wave changes towards lavender versus normal saline in a healthy human population.

This study included a total of 44 participants without subjective olfactory disturbances. Lavender and normal saline were used as the olfactory stimulant and control. Electroencephalogram was recorded and power spectra were analysed by the spectral analysis for each alpha, beta, delta, theta and gamma bandwidth frequency upon exposure to lavender and normal saline independently.

The oscillatory brain activities in response to the olfactory stimulant indicated that the lavender smell decreased the beta activity in the left frontal (F7 electrode) and central region (C3 electrode) with a reduction in the gamma activity in the right parietal region (P4 electrode) (p < 0.05).

Olfactory stimulants result in changes of electrical brain activities in different brain regions, as evidenced by the topographical brain map and spectra analysis of each brain wave.

To investigate the clinical features, therapeutic efficacy and symptom time course of post-coronavirus disease 2019 parosmia.

A 22-item online questionnaire was distributed to AbScent research group and Facebook coronavirus disease 2019 anosmia group adult members to assess clinical features, interventions and their subjective efficacy for parosmia.

A total of 209 participants (86 per cent females) reported: smell loss on average 3 days after coronavirus symptoms, recovery 4 weeks later, and first parosmia symptoms 12 weeks post infection. Respondents reported 10 per cent body weight loss, and listed onion and garlic as significant parosmia triggers. Regarding quality of life, depression was the most cited item (54 per cent). Smell training was trialled by 74 per cent of participants, followed by nasal corticosteroid spray (49 per cent). Stellate ganglion block, trialled by 16 per cent of respondents, had the highest reported improvement (45 per cent), with 21 per cent reporting a sustained benefit – the highest rate amongst registered treatment options.

Post-coronavirus parosmia has a significant impact and remains challenging to treat. Stellate ganglion block appears to be successful relative to other reported treatments. Further research into the pathophysiology, efficacy and mechanism of stellate ganglion block effect is warranted.

This study aimed to evaluate the recovery of olfactory function at six months in individuals infected with the coronavirus disease 2019 omicron variant, using psychophysical tests.

A prospective case–control study that included severe acute respiratory syndrome coronavirus-2 patients infected in February and March 2022 was conducted. Patients underwent the Sniffin’ Sticks test within 10 days of infection and again after at least 6 months. The olfactory scores were compared with those of a control group.

In all, 102 patients and 120 controls were enrolled in the study. At baseline, 26 patients (25.5 per cent) self-reported smell loss. The median threshold, discrimination and identification score was 33.6 (interquartile range, 12.5) for the cases and 36.5 (interquartile range, 4.38) for the controls (p < 0.001). Based on the threshold, discrimination and identification scores, 12 controls and 34 patients reported olfactory dysfunction (p < 0.001). Eighty cases underwent re-evaluation at six months; the median threshold, discrimination and identification score was 37.1 (interquartile range, 4.75) with no significant differences compared with the controls.

Six months after infection, the prevalence of olfactory dysfunction in patients did not differ significantly from the control population.

Smell impairment affects 60–80 per cent of individuals aged over 80 years. This review aimed to identify any association between vitamin D deficiency and smell impairment, and determine the efficacy of vitamin D to treat smell impairment.

A literature search was conducted across four databases between the years 2000 and 2022. The literature screen was performed by two independent reviewers.

Seven articles were included in this review. Four studies examined the association between vitamin D deficiency and smell impairment, with three studies identifying a significant relationship. Three studies investigated the use of vitamin D as treatment for smell impairment, which found complete resolution or significant symptom improvement after vitamin D deficiency was treated.

This review identified limited studies on this topic. As vitamin D supplementation is relatively cost-efficient, further large-scale studies should be carried out to investigate the efficacy of vitamin D for treating anosmia.

This study aimed to determine the predictors of olfactory improvement after endoscopic sinus surgery among patients with chronic rhinosinusitis with nasal polyps.

This prospective cohort study included patients admitted to a university hospital between 2006 and 2012. Assessment using odour identification testing, a sinonasal symptom questionnaire, the Rhinosinusitis Disability Index and mucus biomarker levels was performed at various time points. Correlation of variables with identification score differences at six post-operative time points and at baseline was performed, followed by multiple linear regression to determine significant predictors at each of the six post-operative time points.

Baseline absence of acute sinusitis, elevated serpin F2 and anterior rhinorrhoea predict early olfactory improvement, whereas baseline allergic rhinitis predicts late olfactory improvement. Baseline odour identification score was the strongest predictor across all time points.

Patients with chronic rhinosinusitis and nasal polyps with worse disease or baseline olfactory function may benefit more from endoscopic sinus surgery in terms of olfactory improvement.

This study aimed to evaluate odour measurements after endoscopic repair of cerebrospinal fluid fistulas.

Demographic characteristics, cerebrospinal fluid leak location, surgical procedure, aetiology and smell test results were retrospectively reviewed.

A total of 27 patients were included. The mean age was 43.52 years. The aetiology was spontaneous in 13 patients (48.1 per cent) and traumatic in 14 patients (51.9 per cent). The skull base defect was at the cribriform plate in 15 patients (55.6 per cent), the frontal sinus posterior wall in 4 patients (14.8 per cent), the sphenoid sinus posterior wall in 4 patients (14.8 per cent), around the anterior ethmoid artery in 2 patients (7.4 per cent), at the ethmoid roof in 1 patient (3.7 per cent) and at the sphenoid sinus posterolateral wall in 1 patient (3.7 per cent). After the comparison of pre-operative and post-operative values in identification, discrimination and threshold categories, a statistically significant difference was seen only in the threshold category (p = 0.014).

The results demonstrated that endoscopic repair of cerebrospinal fluid leak is safe in terms of olfactory functions.

Olfactory impairment may be present among patients with coronavirus disease 2019 self-perceived as asymptomatic. This study aimed to assess olfactory function among these individuals.

A cross-sectional study involving patients with coronavirus disease 2019 self-perceived as asymptomatic was conducted. Assessments included the subjective Malaysian Smell and Taste Questionnaire and the culturally adapted Malaysian version of the objective Sniffin’ Sticks Identification smell test.

In 81 participants (mean age of 31.59 ± 12.04 years), with mean time from diagnosis to smell test of 7.47 ± 3.79 days, subjective assessment showed that 80.2 per cent were asymptomatic (questionnaire score of 6) and 19 per cent had mild symptoms (questionnaire score of 7 and 8). The mean objective smell test score was 10.89 ± 2.11. The prevalence of olfactory impairment was 76.6 per cent among patients with coronavirus disease 2019 self-perceived as asymptomatic. There was no association between the questionnaire and the smell test scores (p = 0.25). There was a correlation between the smell test score and the duration from diagnosis to smell test (p = 0.04).

The objective assessment demonstrated that coronavirus disease 2019 patients who perceived themselves as asymptomatic showed olfactory impairment.

In presentations of anosmia or dysosmia, magnetic resonance imaging may be required to screen for intracranial pathology such as olfactory neuroblastomas and other intracranial masses impacting on the olfactory pathway. This study aimed to establish positive magnetic resonance imaging findings of anosmia or dysosmia for scans performed before the coronavirus disease 2019 pandemic.

The study examined the outcome of patients who presented with isolated olfactory dysfunction and who underwent magnetic resonance imaging between 2015 and 2019.

Of the 131 patients, 41 (31.3 per cent) had normal scan findings, 50 (38.2 per cent) had insignificant paranasal mucosal disease and 6 (4.6 per cent) had mucosal thickening significant enough to require additional intervention. These interventions included repeat nasoendoscopy or commencement of intranasal or oral steroids. No patients had olfactory neuroblastoma.

Only 4.6 per cent of the magnetic resonance imaging scans revealed abnormal findings related to anosmia or dysosmia, and none required ENT surgical intervention. None of the magnetic resonance imaging scans identified an olfactory neuroblastoma or intracranial masses impacting on the olfactory pathway.

This study evaluated the olfactory, sinonasal and mucociliary functions of patients with post-coronavirus disease 2019 long-term persistent olfactory dysfunction.

Three groups of 30 patients each were formed: patients with a history of coronavirus disease 2019 infection with self-reported, persistent, sudden-onset olfactory dysfunction (group 1), patients with a history of coronavirus disease 2019 infection without any self-reported olfactory dysfunction (group 2) and healthy controls with no history of coronavirus disease 2019 infection (group 3). Saccharin time, Sniffin’ Sticks, Turkish Nasal Obstruction Symptom Evaluation and Sino-Nasal Outcome Test 22 scores were compared.

Turkish Nasal Obstruction Symptom Evaluation scores were similar between groups (p = 0.252). Sino-Nasal Outcome Test-22 scores were higher in group 1 than groups 2 and 3 (p < 0.01 and p < 0.001, respectively). Saccharin time was significantly longer in group 1 than groups 2 and 3 (p < 0.05 and p < 0.01, respectively). Group 1 had lower olfactory scores than groups 2 and 3 (p < 0.001 and p < 0.001, respectively).

Mucociliary clearance time was significantly prolonged in patients with post-coronavirus disease 2019 persistent olfactory dysfunction. Coronavirus disease 2019 infection was likely to cause asymptomatic olfactory dysfunction.

Although systemic steroids have been shown to improve olfactory function, topical steroids have not demonstrated the same efficacy. This could a result of limited drug delivery to the narrow, superiorly placed olfactory cleft. This study aimed to examine the penetration of intranasal drugs to the olfactory cleft following endonasal balloon dilatation.

Balloon dilatation was performed in 12 thawed, fresh-frozen cadaver specimens. In the Mygind position, nasal drops mixed with blue food dye were administered into the nostril before and after the dilatation procedure. Endoscopic videos were recorded to assess dye staining of the olfactory cleft and osteo-meatal complex using a 4-point Likert scale.

Prior to balloon dilatation, the mean penetration of nasal drops into the olfactory cleft was 1.34, which improved significantly (p < 0.05) to 2.66 following the procedure. There was no change in dye penetration into the osteo-meatal complex after balloon dilatation.

The results of this exploratory study suggest that balloon dilatation may improve the delivery of nasal drops to the olfactory cleft area. The clinical applicability and impact on olfactory function will require further assessment.

This study aimed to determine the association of some demographic and clinical factors with recovery from olfactory and gustatory dysfunction in coronavirus disease 2019 patients in Iran.

This prospective cohort study was performed on 242 coronavirus disease 2019 patients with olfactory and gustatory dysfunction. The time from onset to recovery for olfactory and gustatory dysfunction was estimated by the Kaplan–Meier estimator.

After six months, 239 patients (98.8 per cent) had completely recovered from olfactory dysfunction. Olfactory and gustatory dysfunction symptoms resolved in 80.99 per cent and 83.56 per cent of the patients, respectively, within the first 30 days of symptom onset. Mean recovery time for olfactory dysfunction (35.07 ± 4.25 days) was significantly longer in those infected during the first epidemic wave compared with those infected during the second wave (21.65 ± 2.05 days) (p = 0.004). A similar pattern in recovery time was observed for cases of gustatory dysfunction (p = 0.005).

The recovery rate for coronavirus disease 2019 related olfactory and gustatory dysfunction is high within the first month of symptom onset.

This study aimed to assess the olfactory recovery rates and patterns in a cohort of coronavirus disease 2019 positive patients, and to investigate the clinical predictors of poor long-term olfactory restoration.

An observational retrospective study was conducted on 146 patients between September 2020 and January 2021 at a tertiary referral hospital. Coronavirus disease 2019 positive patients with olfactory dysfunction were sent a modified version of the COVID-19 Anosmia Reporting Tool for Clinicians via e-mail.

The difference in median recovery time between complete recovery and incomplete or no recovery was statistically significant. On multivariate analysis, the only significant factor associated with incomplete or no recovery was anosmia duration.

After a mean time of 5.6 months from severe acute respiratory syndrome coronavirus-2 infection, persistent olfactory disorders were self-reported in 36.7 per cent of patients. Complete recovery was more likely to occur within 15 days. Given the high prevalence of coronavirus disease 2019, a large number of patients are expected to suffer from long-term olfactory morbidity.

This study aimed to investigate the association of nasal nitric oxide and olfactory function.

A cross-sectional study was performed in 117 adults, including 91 patients with chronic rhinosinusitis and 26 healthy controls. Scores on the 22-item Sino-Nasal Outcomes Test, Lund-Mackay scale and Lund-Kennedy scale were recorded to assess severity of disease. All participants were screened for common inhaled and food allergens. Nasal nitric oxide and fractional exhaled nitric oxide testing, acoustic rhinometry and anterior rhinomanometry testing were performed to measure nasal function. The validated Sniffin’ Sticks test battery was used to assess olfactory function.

Higher nasal nitric oxide was an independent protective factor for odour discrimination and odour threshold in participants with chronic rhinosinusitis after adjusting for age, gender, drinking, smoking, 22-item Sino-Nasal Outcomes Test, Lund-Mackay score, Lund-Kennedy score, immunoglobulin E and the second minimal cross-sectional area by acoustic rhinometry. Nasal nitric oxide also showed high discrimination in predicting impaired odour discrimination. In addition, nasal nitric oxide was lower in older participants, those with higher Lund-Mackay or Lund-Kennedy scores and higher with elevated total serum immunoglobulin E concentrations above a threshold of 0.35 kU/l.

Higher nasal nitric oxide is associated with better odour discrimination in chronic rhinosinusitis and is modulated by age, degree of allergy and severity of chronic rhinosinusitis.

Impaired olfaction may be a biomarker for early Lewy body disease, but its value in mild cognitive impairment with Lewy bodies (MCI-LB) is unknown. We compared olfaction in MCI-LB with MCI due to Alzheimer’s disease (MCI-AD) and healthy older adults. We hypothesized that olfactory function would be worse in probable MCI-LB than in both MCI-AD and healthy comparison subjects (HC).

Cross-sectional study assessing olfaction using Sniffin’ Sticks 16 (SS-16) in MCI-LB, MCI-AD, and HC with longitudinal follow-up. Differences were adjusted for age, and receiver operating characteristic (ROC) curves were used for discriminating MCI-LB from MCI-AD and HC.

Participants were recruited from Memory Services in the North East of England.

Thirty-eight probable MCI-LB, 33 MCI-AD, 19 possible MCI-LB, and 32HC.

Olfaction was assessed using SS-16 and a questionnaire.

Participants with probable MCI-LB had worse olfaction than both MCI-AD (age-adjusted mean difference (B) = 2.05, 95% CI: 0.62–3.49, p = 0.005) and HC (B = 3.96, 95% CI: 2.51–5.40, p < 0.001). The previously identified cutoff score for the SS-16 of ≤ 10 had 84% sensitivity for probable MCI-LB (95% CI: 69–94%), but 30% specificity versus MCI-AD. ROC analysis found a lower cutoff of ≤ 7 was better (63% sensitivity for MCI-LB, with 73% specificity vs MCI-AD and 97% vs HC). Asking about olfactory impairments was not useful in identifying them.

MCI-LB had worse olfaction than MCI-AD and normal aging. A lower cutoff score of ≤ 7 is required when using SS-16 in such patients. Olfactory testing may have value in identifying early LB disease in memory services.

The primary goal of this study was to evaluate the association between olfactory dysfunction or taste impairment and disease severity and radiological findings in coronavirus disease-2019. The secondary goal was to assess the prevalence, severity and course of olfactory dysfunction or taste impairment in patients with coronavirus disease 2019.

This prospective observational cohort study evaluated patients hospitalised with coronavirus disease 2019 between April 1 and 1 May 2020. Olfactory dysfunction and taste impairment were evaluated by two questionnaires. Chest computed tomography findings and coronavirus disease-2019 severity were assessed.

Among 133 patients, 23.3 per cent and 30.8 per cent experienced olfactory dysfunction and taste impairment, respectively, and 17.2 per cent experienced both. The mean age was 56.03 years, and 64.7 per cent were male and 35.3 per cent were female. No statistically significant association was found between olfactory dysfunction (p = 0.706) and taste impairment (p = 0.35) with either disease severity or chest computed tomography grading.

Olfactory dysfunction or taste impairment does not have prognostic importance in patients with coronavirus disease 2019.

Despite the rapidly emerging reports of olfactory dysfunction amongst adult patients with coronavirus disease 2019, cases involving children and adolescents are scarcely reported. The literature was reviewed to elucidate olfactory dysfunction amongst children and adolescents with coronavirus disease 2019.

A search of the literature published from 1 December 2019 to 30 April 2021 was conducted using four databases, based on Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines and the Cochrane Handbook for Systematic Reviews of Interventions. The search was performed over one month (May 2021).

Only 9 articles were identified, with a total of 316 laboratory confirmed coronavirus disease 2019 positive children and adolescents, of whom 156 reported olfactory dysfunction. Four studies reported olfactory dysfunction based on subjective tests; four studies carried out objective assessment. Most studies reported on olfaction recovery.

The literature review revealed an olfactory dysfunction rate of 49 per cent amongst children and adolescents with coronavirus disease 2019. Persistence of olfactory dysfunction was reported in 7.1 per cent of the patients. Further studies involving objective measures need to be carried out in children and adolescents with coronavirus disease 2019.