Recent anecdotal and scientific reports have provided evidence of a link between COVID-19 and chemosensory impairments such as anosmia. However, these reports have downplayed or failed to distinguish potential effects on taste, ignored chemesthesis, and generally lacked quantitative measurements. Here, we report the development, implementation and initial results of a multi-lingual, international questionnaire to assess self-reported quantity and quality of perception in three distinct chemosensory modalities (smell, taste, and chemesthesis) before and during COVID-19. In the first 11 days after questionnaire launch, 4039 participants (2913 women, 1118 men, 8 other, ages 19-79) reported a COVID-19 diagnosis either via laboratory tests or clinical assessment. Importantly, smell, taste and chemesthetic function were each significantly reduced compared to their status before the disease. Difference scores (maximum possible change ±100) revealed a mean reduction of smell (-79.7 ± 28.7, mean ± SD), taste (-69.0 ± 32.6), and chemesthetic (-37.3 ± 36.2) function during COVID-19. Qualitative changes in olfactory ability (parosmia and phantosmia) were relatively rare and correlated with smell loss. Importantly, perceived nasal obstruction did not account for smell loss. Furthermore, chemosensory impairments were similar between participants in the laboratory test and clinical assessment groups. These results show that COVID-19-associated chemosensory impairment is not limited to smell, but also affects taste and chemesthesis. The multimodal impact of COVID-19 and lack of perceived nasal obstruction suggest that SARS-CoV-2 infection may disrupt sensory-neural mechanisms.

The olfactory test battery "Sniffin'Sticks" comprises a perception threshold test, an odour discrimination test and an odour identification test. The purpose of this study was to examine the suitability of the Sniffin'Sticks for use in everyday practice and to obtain (at least provisional) normal values. Thirty normosmic and 15 anosmic volunteers were examined with the Sniffin'Sticks and the "University of Pennsylvania Smell Identification Test" (UPSIT). All three Sniffin'Sticks tests distinguish between normosmics and anosmics in a highly significant manner. The good correlation of the individual tests with each other and with the results of the UPSIT documents the reliability of the test results. Critical mention must be made of the overly complex determination of the olfactory threshold. In conclusion, the Sniffin'Sticks test battery provides a validated instrument adapted to European conditions for the examination of olfactory disorders. It has proven successful in everyday clinical practice and constitutes a major aid for compiling medical certificates.

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Postviral olfactory disorders usually occur after an upper respiratory tract infection (URTI) associated with a common cold or influenza. With a prevalence between 11 and 40% they are among the common causes of olfactory disorders. Women are more often affected than men and post-URTI disorders usually occur between the fourth and eighth decade of life. The exact location of the damage in post-URTI is not yet known even though from biopsies a direct damage of the olfactory receptor cells is very likely. Nevertheless, central mechanisms cannot completely be ruled out. The diagnosis is made according to the history, clinical examination and olfactory testing. Affected patients usually recall the acute URTI and a close temporal connection should be present to establish the diagnosis. Spontaneous recovery might occur within 2 years. So far, no effective therapy exists even though specific olfactory training might be promising.

Olfactory dysfunction is a frequent nonmotor symptom in idiopathic Parkinson's disease (PD) and may be considered as an early clinical feature of the disease preceding motor symptoms by years. According to recent neuropathological staging concepts, impaired olfaction is assumed to indicate an early pathological process and might be associated with structural changes in the brain. A morphometric analysis of magnetic resonance images [voxel-based morphometry (VBM)] was used to investigate gray matter atrophy related to psychophysically measured scores of olfactory function in early PD patients (n ϭ 15, median Hoehn and Yahr stage 1.5), moderately advanced PD patients (n ϭ 12, median Hoehn and Yahr stage 2.5), and age-matched healthy controls (n ϭ 17). In PD patients, but not in controls, cortical atrophy in olfactory-related brain regions correlated specifically with olfactory dysfunction. Positive correlations between olfactory performance and gray matter volume were observed in the right piriform cortex in early PD patients and in the right amygdala in moderately advanced patients. The results provided first evidence that olfactory dysfunction in PD is related to atrophy in olfactory-eloquent regions of the limbic and paralimbic cortex. In addition, olfactory-correlated atrophy in these brain regions is consistent with the assumption that olfactory impairment as an early symptom of PD is likely to be associated with extranigral pathology.

Although 5% of the general population exhibit a functional anosmia, little is known about the frequency of gustatory disorders. Whenever taste function has been tested within large sociodemographic studies, so far only short test versions were applied making the interpretation difficult. Using two psychophysical taste tests, the validated "taste strips" and suprathreshold taste solutions of the four basic tastes sweet, sour, salty and bitter we investigated 761 healthy subjects within the age range of 5-89 years. Prior to testing, all subjects rated their taste function. According to testing with the taste strips, 5.3% scored below the result considered as hypogeusia. All four taste sprays were correctly identified by 82.3% of all subjects. Results of the two taste tests correlated positively (r = 0.33, p < 0.001), and there was a significant negative correlation between age and test results. However, we never observed complete ageusia. Misinterpretations of tastes were surprisingly common. In summary, hypogeusia was present in 5% while complete ageusia seems to be very rare, in contrast to misinterpretations of tastes.

In patients with PD, results obtained under the specific conditions used suggest that neuronal activity in the amygdala and hippocampus is reduced. Assuming an impact on olfactory-related regions early in PD, our findings support the idea that selective impairment of these brain regions contributes to olfactory dysfunction. Furthermore, neuronal activity in components of the dopaminergic, cortico-striatal loops appears to be upregulated, indicating that compensatory processes are involved. This mechanism has not yet been demonstrated during olfactory processing in PD.

Objectives: Olfactory dysfunction is a common problem. However, too little attention has been paid to questionnaires used to evaluate quantitative olfactory dysfunction. Therefore, the current study aimed to develop a simple self-reported Mini Olfactory Questionnaire (Self-MOQ) for the screening of quantitative olfactory dysfunction in clinical practice. Methods: Two hundred and eighty-five patients who had subjective complaints of olfactory disorder participated. The Sniffin' Sticks test score was used to define functional anosmia, hyposmia, or normosmia. We assessed the factor structure as well as internal consistency, convergent validity, and discrimination performance. Results: The results showed that the final version of the Self-MOQ included only one factor with five items. The Self-MOQ has a good internal reliability (Cronbach's α = 0.84) and validity (r = −0.60, P < 0.001). The receiver operating characteristic analyses indicated that the Self-MOQ as compared to a visual analogue scale (VAS) is an effective measure for discriminating normosmic from hyposmic/anosmic patients, anosmic patients, and hyposmic patients. Conclusion: The Self-MOQ is a simple, reliable and valid questionnaire to screen olfactory dysfunction in clinical practice that appears to be superior to the use of VASs but does not replace olfactory testing.