Central presentation of postviral olfactory loss evaluated by positron emission tomography scan: A pilot study

Abstract

Background Postviral olfactory loss after upper respiratory tract infection (URI) is not uncommon. However, its exact location and nature are not fully understood. Although it is likely to be caused by a direct damage of olfactory epithelium, a damage of the central pathway has also been suspected as its possible mechanism. This study will show basal metabolism in the brain of patients with postviral olfactory loss using fluorodeoxyglucose-positron emission tomography (FDG PET). Methods Nine patients with postviral olfactory dysfunction were enrolled. All of the patients had neither apparent sinusitis nor rhinitis. All of them recalled causative URI and temporal connection with development of their olfactory loss. After olfactory function tests using the butanol threshold test and smell identification test confirmed olfactory impairment, FDG PET studies were performed during a rest state. The cerebral metabolic abnormality was compared between the patients and age/gender-matched healthy controls using a voxel-wised analysis. Results In comparison with healthy controls, the patients showed a significant hypometabolism in the right piriform cortex and bilateral amygdala and parahippocampal areas where the olfactory neurons primarily project. Furthermore, hypometabolism was also shown in the bilateral insular cortices, medial and lateral temporal cortex where the olfactory information is integrated to produce the sensation. Increased metabolism was not found in any brain area. Conclusion This study showed that the postviral olfactory loss is likely to be associated with decreased metabolism in the specific brain regions where the olfactory information is received and integrated.

New loss of smell and taste: Uncommon symptoms in COVID-19 patients on Nord Franche-Comte cluster, France

“…For example, in patients with POL, the main suspected mechanism is a damage of olfactory epithelium: we know that MRI of the olfactory bulb show a reduction of its volume ( Rombaux et al, 2006 ) and biopsy of the olfactory cleft reveal a diminution of the olfactory receptors ( Yamagishi et al, 1994 ). However, central damage during viral infection are also suspected ( Kim et al, 2012 ). Different kind of viruses can induce a POL, including coronaviruses ( Chen et al, 2020 ).…”

Clinical features of COVID-19 and influenza: a comparative study on Nord Franche-Comte cluster

“…These notions led to suspect another pathogenesis than a nasal obstruction for anosmia, as it is described in post-viral olfactory loss (POL) which can also be associated with dysgeusia [15]. The pathogenesis of POL involves probably a damage of the sensory receptors [16] or a lesion of the neural system (olfactory cranial nerve or central lesion) [17].…”

COVID-19-Related Anosmia: The Olfactory Pathway Hypothesis and Early Intervention

“…Furthermore, 70% of patients who reported complete resolution proved hyposmic to an objective test. Also, the study population subgroup analysis showed a high frequency of olfactory disorders throughout the observation period, ranging between 77.4% (days 1-4) and 69.2% (days [25][26][27][28][29][30][31][32][33][34][35]. Anosmia or severe hyposmia affected 70.9% of patients in the early stages; they improved after the first 10 days, reaching moderate hyposmia values.…”

“…On the contrary, Kim and Hong demonstrated that persistent PVOD is associated with decreased metabolism in specific brain regions where the olfactory stimuli are processed and integrated, suggesting that anosmia is, in some cases, caused by a central injury mechanism (25). Virally induced damage of OB and other brain areas was highlighted through magnetic resonance imaging correlating olfactory function with OB volume (26).…”