Loss of smell during COVID linked to structural, functional brain alterations
Many individuals who lost their sense of smell when infected with COVID-19 show structural and functional brain alterations on imaging, according to new work published in Nature.
Near the onset of the pandemic, when tests for the virus varied in their reliability and a COVID diagnosis was a nearly automatic isolation sentence, anosmia became a telltale sign of infection. According to data shared by the Centers for Disease Control and Prevention last year, around 34% of patients who contracted COVID between 2020 and 2023 reported losing their sense of smell.
Now, experts are concerned that the symptoms could be associated with long-term brain alterations. In a group of people who reported anosmia as one of their COVID symptoms, experts recently observed an association between the loss of smell and decreased functional activity during decision-making tasks, reduced cortical thickness and other neural measures. These findings indicate that patients who report issues with smell during a bout with COVID may need additional, targeted follow-up, the group suggested.
“This symptom can serve as a clinical, and in some cases a preclinical, indicator of neurological diseases such as Alzheimer's disease, Huntington's disease, Parkinson's disease, vascular dementia, and mild cognitive impairment, among others,” co-corresponding author Pablo Billeke, with the Laboratory of Neuroscience and Neuromodulation in Santiago, Chile, and colleagues explain. “Therefore, objective evaluations and follow-up are required.”
For the study, researchers conducted an array of tests, including cognitive screenings, decision-making tasks and MRI evaluations, on a sample of 100 patients—73 who had prior mild to moderate COVID and 27 who had never contracted the virus. The team looked for variations in behavior, neural activity and brain structure between patients who experienced anosmia and those who did not.
Patients who reported losing their sense of smell showed altered olfactory network connectivity. However, these individuals also reported having issues with memory and mood disturbances since recovering from the virus.
The symptom also was associated with decreased BOLD signal during decision-making in the lateral prefrontal, medial frontal and left temporoparietal regions of the brain. The loss of white matter integrity and reduced cortical thickness were also observed in this group.
The team pointed to a prior EEG/fNIRS study that found similar functional alterations in patients with anosmia, suggesting that the “deficits, although subtle, could have long-term implications for quality of life and cognitive performance.”
The group suggested that the symptom be taken into more serious consideration when treating patients who may be struggling with lingering symptoms of COVID, such as fatigue, mood disorders and cognitive struggles.
“These findings contribute to our understanding of the neurological consequences of COVID-19 and underscore the importance of early detection and intervention in at-risk populations.”
The study can be viewed here.
In addition to her background in journalism, Hannah also has patient-facing experience in clinical settings, having spent more than 12 years working as a registered rad tech. She began covering the medical imaging industry for Innovate Healthcare in 2021.