Brain Imaging Points to Possible Reason for Persistent Smell, Taste Trouble in COVID Patients

By Megan Brooks

January 26, 2021

NEW YORK (Reuters Health) - Impairment of the central olfactory pathway, mainly involving the orbitofrontal cortex (OFC), may underlie persistent impairment in smell and taste in patients after COVID-19 infection, clinicians report.

Dr. Khaled Gad and Dr. Ismail Ibrahim Ismail of Ibn Sina Hospital, Sabah Health Region, Kuwait, describe a 25-year-old previously healthy woman with COVID-19 who developed fever, generalized body pain, dry cough, anosmia and ageusia.

Her clinical course was uncomplicated, and she was treated conservatively. And while anosmia and ageusia began to improve during recovery, she started to suffer offensive odor (cacosmia) and taste (cacogeusia) with stimulation of these sensations. Ear, nose, and throat evaluation was normal and CT findings of the paranasal sinuses were unremarkable.

Findings of her neurological examination were also normal, the clinician report in JAMA Neurology. Brain magnetic resonance imaging (MRI) showed normal findings, including the olfactory bulbs and sulci, with no structural or signal abnormality.

The patient underwent a task-based functional MRI (f-MRI) study with alternating blocks of smell activation by a pleasant scent intervened with periods of rest. The researchers generated blood oxygen level-dependent (BOLD) activation maps fused to T1-weighted multiplanar images. The noteworthy finding, they say, was "absent activation in the region of the OFC, while the right uncus/piriform cortex demonstrated strong BOLD signal."

"The utility of fMRI in patients with COVID-19 is not well established, and to our knowledge, this is the first published report using fMRI in a patient with persistent cacosmia and cacogeusia after COVID-19 infection," they write in their paper.

In a joint email to Reuters Health, Dr. Ismail and Dr. Gad said it was important to publish this case report for two reasons.

"First, the technical success we were able to achieve by designing the f-MRI study of olfaction given the fact that this has always been challenging to perform," they said.

"Second, we'd like to convey a clear message to clinicians and other professionals highlighting the potential complexity (of the effects on smell) in COVID-19. We were able to focus on the possible alteration at the level of functional brain networks in the absence of apparent structural lesions shedding light on how this virus might be responsible for scenarios that require further research to understand."

Since publication of the case-report, they say, the patient has been performing olfactory training, "with a very slight improvement of the offensive odors and taste after 9 months of COVID-19 infection. She still reports avoiding certain odors (e.g. perfumes) and certain foods (e.g. fish, meat) because she still perceives them as offensive."

SOURCE: JAMA Neurology, online January 22, 2021.