Loss of Smell and Taste in COVID-19 Patients Linked to Orbitofrontal Cortex

Loss of Smell and Taste in COVID-19 Patients Linked to Orbitofrontal Cortex

Infection with SARS-CoV-2 often sees patients temporarily lose the senses of smell (anosmia) and taste (ageusia), but why this occurs with COVID-19 is not well understood. A study of patients using functional MRI (fMRI) imaging has provided some insights into how and why this occurs.

Researchers at Ibn Sina hospital in Kuwait report that between 43.9% and 52.7% of patients with COVID-19 suffer loss of the senses of smell and taste after contracting COVID-19.

Khaled A. Gad, M.D., and Ismail Ibrahim Ismail, MSc, who work in the Radiology and neurology departments respectively at Ibn Sina hospital, detailed their experience with a 25-year-old female patient with COVID-19 who lost both senses following SARS-CoV-2 infection.

Doctors at the hospital provided conservative treatment and the patient’s symptoms started to improve, although after a month she complained about cacosmia and cacogeusia, which are sensations from offensive odors and tastes. Tests on the patient revealed no abnormalities in her ears, nose, and throat, and an MRI scan of her olfactory bulbs and sulci appeared normal with no structural abnormalities. The patient was prescribed oral and intranasal corticosteroids, multivitamins and zinc, and underwent olfactory training, but even with these treatments the cacosmia and cacogeusia continued for three months.

An fMRI study was then commissioned to further examine the patient’s symptoms. In the study, the patient underwent alternated blocks of smell with pleasant scents followed by periods of rest. Blood oxygen level-dependent (BOLD) activation maps were fused to T1-weighted multi-planar images, which revealed a lack of activation in the orbitofrontal cortex (OFC), but an almost consistent pattern of BOLD activation in the primary and secondary olfactory areas.

The OFC contains the secondary and tertiary olfactory and gustatory cortex areas, where processing of olfactory and gustatory information occurs. “Given these findings, we could suggest central olfactory pathway impairment, mainly involving OFC, may be involved in the underlying etiology of persistence of olfactory and gustatory symptoms in patients after COVID-19 infection,” suggested the researchers, indicating SARS-CoV-2 may invade the brain through the olfactory pathway.

You can read more about the study in the paper – Absent Blood Oxygen Level–Dependent Functional Magnetic Resonance Imaging Activation of the Orbitofrontal Cortex in a Patient With Persistent Cacosmia and Cacogeusia After COVID-19 Infection – which was recently published in the JAMA Neurology. DOI: 10.1001/jamaneurol.2021.0009

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