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Journal of Neurophysiology Aug 2022Olfactory dysfunction is a hallmark symptom of COVID-19 disease resulting from the SARS-CoV-2 virus. The cause of the sudden and usually temporary anosmia that most... (Review)
Review
Olfactory dysfunction is a hallmark symptom of COVID-19 disease resulting from the SARS-CoV-2 virus. The cause of the sudden and usually temporary anosmia that most people suffer from COVID-19 is likely entirely peripheral-inflammation and other damage caused by the virus in the sensory epithelium inside the upper recesses of the nasal cavity can damage or prevent chemicals from properly activating the olfactory sensory neurons. However, persistent olfactory dysfunction from COVID-19, in the form of hyposmia and parosmia (decreased or altered smell) may affect as many as 15 million people worldwide. This epidemic of olfactory dysfunction is thus a continuing public health concern. Mounting evidence suggests that the SARS-CoV-2 virus itself or inflammation from the immune response in the nasal sensory epithelium may invade the olfactory bulb, likely via non-neuronal transmission. COVID-19-related long-term olfactory dysfunction and early damage to olfactory and limbic brain regions suggest a pattern of degeneration similar to that seen in early stages of Alzheimer's disease, Parkinson's disease, and Lewy body dementia. Thus, long-term olfactory dysfunction coupled with cognitive and emotional disturbance from COVID-19 may be the first signs of delayed onset dementia from neurodegeneration. Few treatments are known to be effective to prevent further degeneration, but the first line of defense against degeneration may be olfactory and environmental enrichment. There is a pressing need for more research on treatments for olfactory dysfunction and longitudinal studies including cognitive and olfactory function from patients who have recovered from even mild COVID-19. More than 15 million people worldwide experience persistent COVID-19 olfactory dysfunction, possibly caused by olfactory bulb damage. SARS-CoV-2 can cause inflammation and viral invasion of the olfactory bulb, initiating a cascade of degeneration similar to Alzheimer's disease and Lewy body disease. People who have had even mild cases of COVID-19 show signs of degeneration in cortical areas connected with the olfactory system. These data suggest a wave of post-COVID dementia in the coming decades.
Topics: Alzheimer Disease; COVID-19; Humans; Inflammation; Olfaction Disorders; Olfactory Bulb; SARS-CoV-2; Smell
PubMed: 35894511
DOI: 10.1152/jn.00255.2022 -
Neuropsychology Review Mar 2024Olfactory training (OT), or smell training,consists of repeated exposure to odorants over time with the intended neuroplastic effect of improving or remediating... (Review)
Review
Olfactory training (OT), or smell training,consists of repeated exposure to odorants over time with the intended neuroplastic effect of improving or remediating olfactory functioning. Declines in olfaction parallel declines in cognition in various pathological conditions and aging. Research suggests a dynamic neural connection exists between olfaction and cognition. Thus, if OT can improve olfaction, could OT also improve cognition and support brain function? To answer this question, we conducted a systematic review of the literature to determine whether there is evidence that OT translates to improved cognition or altered brain morphology and connectivity that supports cognition. Across three databases (MEDLINE, Scopus, & Embase), 18 articles were identified in this systematic review. Overall, the reviewed studies provided emerging evidence that OT is associated with improved global cognition, and in particular, verbal fluency and verbal learning/memory. OT is also associated with increases in the volume/size of olfactory-related brain regions, including the olfactory bulb and hippocampus, and altered functional connectivity. Interestingly, these positive effects were not limited to patients with smell loss (i.e., hyposmia & anosmia) but normosmic (i.e., normal ability to smell) participants benefitted as well. Implications for practice and research are provided.
Topics: Humans; Brain; Cognition; Olfaction Disorders; Olfactory Training; Smell
PubMed: 36725781
DOI: 10.1007/s11065-022-09573-0 -
The Journal of Allergy and Clinical... Apr 2023
Topics: Humans; COVID-19; SARS-CoV-2; Olfaction Disorders; Smell
PubMed: 36813187
DOI: 10.1016/j.jaci.2023.02.007 -
Oral Diseases Nov 2022The COVID-19 pandemic caused by SARS-CoV-2 virus quickly spread globally, infecting over half a billion individuals, and killing over 6 million*. One of the more unusual... (Review)
Review
The COVID-19 pandemic caused by SARS-CoV-2 virus quickly spread globally, infecting over half a billion individuals, and killing over 6 million*. One of the more unusual symptoms was patients' complaints of sudden loss of smell and/or taste, a symptom that has become more apparent as the virus mutated into different variants. Anosmia and ageusia, the loss of smell and taste, respectively, seem to be transient for some individuals, but for others persists even after recovery from the infection. Causes for COVID-19-associated chemosensory loss have undergone several hypotheses. These include non-functional or destroyed olfactory neurons and gustatory receptors or of their supporting cells, disruption of the signaling protein Neuropilin-1, and disruption in the interaction with semaphorins, key molecules in the gustatory and olfactory axon guidance. The current paper will review these hypotheses and chart out potential therapeutic avenues.
Topics: Humans; COVID-19; Pandemics; SARS-CoV-2; Taste Disorders; Olfaction Disorders; Anosmia
PubMed: 35790059
DOI: 10.1111/odi.14300 -
Chemical Senses Jan 2021Among those many individuals who experience a reduced odor sensitivity (hyposmia/anosmia), some individuals also have disorders that lead to odor distortion, such as...
Among those many individuals who experience a reduced odor sensitivity (hyposmia/anosmia), some individuals also have disorders that lead to odor distortion, such as parosmia (i.e. distorted odor with a known source), or odor phantoms (i.e. odor sensation without an odor source). We surveyed a large population with at least one olfactory disorder (N = 2031) and found that odor distortions were common (46%), with respondents reporting either parosmia (19%), phantosmia (11%), or both (16%). In comparison to respondents with hyposmia or anosmia, respondents with parosmia were more likely to be female, young, and suffering from post-viral olfactory loss (P < 0.001), while respondents with phantosmia were more likely to be middle-aged (P < 0.01) and experiencing symptoms caused by head trauma (P < 0.01). In addition, parosmia, compared to phantosmia or anosmia/hyposmia, was most prevalent 3 months to a year after olfactory symptom onset (P < 0.001), which coincides with the timeline of physiological recovery. Finally, we observed that the frequency and duration of distortions negatively affects the quality of life, with parosmia showing a higher range of severity than phantosmia (P < 0.001). Previous research often grouped these distortions together, but our results show that they have distinct patterns of demographics, medical history, and loss in quality of life.
Topics: Female; Humans; Male; Middle Aged; Odorants; Olfaction Disorders; Prevalence; Quality of Life; Smell
PubMed: 34698820
DOI: 10.1093/chemse/bjab046 -
Ugeskrift For Laeger Feb 2023Change in olfactory and/or gustatory dysfunction have gained attention in recent years because of COVID-19. However, these symptoms are common and have numerous... (Review)
Review
Change in olfactory and/or gustatory dysfunction have gained attention in recent years because of COVID-19. However, these symptoms are common and have numerous different aetiologies, which should not be forgotten. Adequate diagnostic work up and clinical examination is essential. Treatment may include olfactory training, topically applied steroids and perhaps surgery. This review summarises common reversible causes of olfactory and/or gustatory dysfunction and current treatment modalities.
Topics: Humans; COVID-19; SARS-CoV-2; Olfaction Disorders; Smell; Taste Disorders
PubMed: 36892317
DOI: No ID Found -
Science Translational Medicine Dec 2022SARS-CoV-2 causes profound changes in the sense of smell, including total smell loss. Although these alterations are often transient, many patients with COVID-19 exhibit...
SARS-CoV-2 causes profound changes in the sense of smell, including total smell loss. Although these alterations are often transient, many patients with COVID-19 exhibit olfactory dysfunction that lasts months to years. Although animal and human autopsy studies have suggested mechanisms driving acute anosmia, it remains unclear how SARS-CoV-2 causes persistent smell loss in a subset of patients. To address this question, we analyzed olfactory epithelial samples collected from 24 biopsies, including from nine patients with objectively quantified long-term smell loss after COVID-19. This biopsy-based approach revealed a diffuse infiltrate of T cells expressing interferon-γ and a shift in myeloid cell population composition, including enrichment of CD207 dendritic cells and depletion of anti-inflammatory M2 macrophages. Despite the absence of detectable SARS-CoV-2 RNA or protein, gene expression in the barrier supporting cells of the olfactory epithelium, termed sustentacular cells, appeared to reflect a response to ongoing inflammatory signaling, which was accompanied by a reduction in the number of olfactory sensory neurons relative to olfactory epithelial sustentacular cells. These findings indicate that T cell-mediated inflammation persists in the olfactory epithelium long after SARS-CoV-2 has been eliminated from the tissue, suggesting a mechanism for long-term post-COVID-19 smell loss.
Topics: Animals; Humans; COVID-19; Anosmia; SARS-CoV-2; RNA, Viral; Olfaction Disorders; Olfactory Mucosa; Gene Expression
PubMed: 36542694
DOI: 10.1126/scitranslmed.add0484 -
International Forum of Allergy &... Nov 2020
Topics: Humans; Odorants; Olfaction Disorders; Olfactory Bulb; Smell
PubMed: 32776673
DOI: 10.1002/alr.22681 -
Cell and Tissue Research Jan 2021The sense of smell essentially contributes to social communication, guides nutrition behaviour and elicits avoidance towards environmental hazards. Olfactory smell... (Review)
Review
The sense of smell essentially contributes to social communication, guides nutrition behaviour and elicits avoidance towards environmental hazards. Olfactory smell impairment may hence entail severe consequences for affected individuals. Compared with sensory loss in other modalities, reduced olfactory function is often unnoticed by those affected and diagnosed late. Those patients seeking help frequently suffer from long-term impairments resulting in reduced well-being and quality of life. The current review provides an overview of aetiology, prevalence and specifics of diagnostics in acquired and congenital olfactory loss and focusses on short- and long-term consequences. Compensation strategies are elaborated, and treatment options are mentioned. Individual characteristics associated with the development of serious mental health impairment are discussed in order to help practitioners identifying populations at risk.
Topics: Humans; Olfaction Disorders
PubMed: 33496882
DOI: 10.1007/s00441-020-03381-9 -
Journal of Investigational Allergology... 2020The first cases of coronavirus 2019 disease (COVID-19) occurred in Wuhan, China, and the disease rapidly become a public health emergency of international proportions.... (Review)
Review
The first cases of coronavirus 2019 disease (COVID-19) occurred in Wuhan, China, and the disease rapidly become a public health emergency of international proportions. COVID-19 can cause mild-to-severe acute respiratory syndrome (SARS) and is caused by the SARS-CoV-2 coronavirus. The clinical manifestations of COVID-19 include fever, dry cough, fatigue, sputum production, shortness of breath, sore throat, and headache. We performed this narrative review to analyze the current literature on postviral olfactory dysfunction related to the SARSCoV- 2 pandemic. Since the initial anecdotal reports from China, increasingly frequent international reports on COVID-19 indicate that 5% to 85% of affected patients lose their sense of smell, thus highlighting the very heterogeneous nature of the literature in this area. Therefore, we advise home isolation measures and/or social distancing, as well as tests to detect SARS-CoV-2 when possible, in patients with sudden and severe loss of smell who cannot be promptly evaluated.
Topics: Betacoronavirus; COVID-19; Coronavirus Infections; Disease Outbreaks; Female; Humans; Male; Olfaction Disorders; Olfactory Bulb; Pandemics; Pneumonia, Viral; SARS-CoV-2; Smell
PubMed: 32406374
DOI: 10.18176/jiaci.0567