fMRI Identifies Smell and Taste Malfunction in COVID-19 Patients

Functional MRI (fMRI) has helped increase understanding about the loss of smell and taste that frequently accompany COVID-19 infection. The answer lies in the orbitofrontal cortex (OFC).

In a case study published Jan. 22 in JAMA Neurology, investigators from Ibn Sina hospital in Kuwait detailed their experience in April 2020 with a 25-year-old, COVID-19-positive female patient who had both anosmia and ageusia – loss of smell and taste, respectively.

Both Khaled A. Gad, M.D., from the Ibn Sina radiology department, and Ismail Ibrahim Ismail, MSc, from the neurology department, outlined the findings. It is the first published report, they said, of using fMRI with COVID-19-positive patients who have lost the senses of smell and taste.

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According to studies conducted throughout the past year, the investigators said, changes in smell and taste are not uncommon with this viral infection. These symptoms affect 52.7 percent and 43.9 percent of COVID-19-positive patients, respectively.

A, Axial T2-weighted image of the brain at the level of medial temporal lobes, gyrus rectus, and orbitofrontal gyrus showing no structural or signal abnormalities. B, Fused blood oxygen level–dependent (BOLD) map on coronal T1-weighted image showing no activation in the region of the orbitofrontal cortex. Credit: JAMA Neurology

Initially, doctors followed a conservative treatment course, and the patient’s anosmia and ageusia began to abate. However, within the month, she began to suffer cacosmia (sensations from offensive odor) and cacogeusia (sensations from offensive taste). Clinical evaluations of her ear, nose, and throat were normal, and CT of the paranasal sinuses were unremarkable, the authors said. MRI of the olfactory bulbs and sulci also appeared normal. To counteract and relieve these symptoms, she was prescribed oral and intranasal corticosteroids, as well as multi-vitamins, zinc, and olfactory training, but her symptoms persisted for three months.

To further examine the patient’s symptoms, the team created a task-based fMRI study that alternated blocks of smell with pleasant scents and periods of rest, fusing generated blood oxygen level-dependent (BOLD) activation maps with T1-weighted multi-planar images.

A, Fused blood oxygen level–dependent (BOLD) map on coronal T1-weighted image showing activation of the right uncus at the region of piriform cortex and at the anterior cingulate. B, Fused BOLD map on axial T1-weighted image showing 2 sites of activation of the right uncus at the region of piriform cortex. T map threshold approximately 40% to 50% (P < .05). Credit: JAMA Neurology

Images captured with fMRI, they said, have revealed a nearly consistent pattern of BOLD activation of primary and secondary olfactory areas, but with this patient, activation was absent in the OFC. The BOLD signal was strong in the right uncus/piriform cortex, however. This finding fell in line with what is being increasingly discovered with COVID-19 patients.

“There is accumulating evidence of implication of OFC in patients with COVID-19 with olfactory dysfunction,” they explained.

Even though the use of fMRI with these patients has not yet been well established, it does offer valuable information that can help providers better understand what is happening with this group.

“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,” they said.

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