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Introduction: Migraine is a leading cause of disability and suffering worldwide. However, conventional pharmacological migraine preventive therapies are often challenging and accompanied by adverse effects. Recently, structured odour exposure has shown to successfully increase pain thresholds in patients with chronic back pain. Despite the importance of the olfactory system in migraine, there are no studies investigating the impact of structured odour exposure in patients with migraine. Methods and analysis: This double-blind randomised placebo-controlled trial will be conducted at the Headache Clinic of the University Pain Center at TU Dresden, Germany and aims at investigating the impact of a 12-week structured exposure to odours in women with migraine. Fifty-four women between 18 and 55 years with migraine with aura will be recruited and randomised to training with odours and odourless training. The primary outcomes are mechanical and electrical pain thresholds. Secondary outcomes comprise olfactory threshold and the number of headache days. Other exploratory measurements are headache associated pain intensity, acute analgesic intake, symptoms of anxiety and depression, and quality of life. Additionally, this protocol assesses neuroanatomical and neurofunctional changes associated with the 12-week olfactory training. Data analysis will be executed on the basis of the general linear model considering repeated measurements. Ethics and dissemination: Ethical approvals were obtained from the Ethics Board of the TU Dresden (Protocol No. BO-EK-353082020). Participation will only be possible after written informed consent is provided. Findings will be disseminated through peer-reviewed journals and scientific conferences.

Introduction: COVID-19 can be associated with a variety of longer-lasting impairments that can have a significant impact on patients' quality of life (QoL). While this is well described in the literature for limitations in lung capacity or permanent headaches, there is little research on the impact of olfactory dysfunction in the context of COVID-19 on patients' QoL. Methods: In 65 patients with a history of COVID-19, the present olfactory ability was assessed using the Sniffin' Sticks test. In addition, olfactory QoL was assessed by the Questionnaire of Olfactory Disorders. Self-assessment was performed with visual analogue scales. The data were compared with the results obtained in healthy individuals and in patients with hyposmia due to other viral infections. Results: The QoL of COVID-19 patients was significantly lower compared to the healthy control group. Even recovered subjects whose olfaction had already returned to the normal range still had a reduced QoL. The severity of the olfactory impairment correlated with the reduction in QoL. However, the olfactory QoL of COVID-19 patients was not worse than that of patients' olfactory loss due to other viral infections. Patients with parosmia had reduced QoL and rated their situation worse than patients without parosmia. Conclusion: QoL appears to be impaired in patients with long-lasting COVID-19 olfactory disorders several months after overcoming acute symptoms, even if olfaction has normalized. However, the impairment is not more pronounced than in patients with other postviral olfactory disorders of the same duration.

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). 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. 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. 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.

Purpose This study aimed to evaluate the course of olfactory dysfunction [OD] due to upper respiratory tract infections [URTI] especially for COVID-19 [C19] in a multicentric design and to investigate possible predictors for the outcome. Methods In a multicentric study, patients (n = 147, of which 96 were women) with OD due to URTI, including C19 and non-C19 were evaluated at two visits with a standardized medical history and “Sniffin’ Sticks” extended psychophysical testing to examine the course and possible predictors for improvement of olfactory function. Results C19 patients showed better overall olfactory function (p < 0.001) compared to non-C19. Olfactory function (p < 0.001) improved over 3.5 ± 1.2 months in a comparable fashion for C19 and non-C19 comparable over time (p = 0.20) except for a more pronounced improvement of odour threshold (p = 0.03) in C19. C19 patients with parosmia exhibited a higher probability of clinically relevant improvement of odour threshold, a better threshold in the second visit, and tended to have a better TDI-score at the second visit. Further possible predictors for an improving olfactory function were younger age, female gender, and had lower scores in olfactory tests at the first visit. Conclusions Patients with C19 and non-C19 URTI exhibit a similar improvement over 3–4 months except for the odour threshold, with a better TDI in both visits for C19. For C19 a better prognosis in terms of olfactory recovery was found for younger patients with parosmia and lower olfactory scores at the first visit. Still, for many patients with olfactory loss, an improvement that is experienced as complete may only occur over months and possibly years.