Dopamine Loss Linked to Long COVID Fatigue
A new brain imaging study published in the journal eBioMedicine provides evidence that long COVID is linked to injury in the brain’s dopamine-releasing neurons. Researchers at the Centre for Addiction and Mental Health (CAMH) found that reduced dopamine nerve terminal density in the striatum correlates with common long COVID symptoms, including fatigue, memory difficulties, and slowed movement.
Mapping Neurological Damage
Researchers utilized positron emission tomography (PET) scans to evaluate the integrity of dopamine neurons in individuals suffering from long COVID compared to healthy control subjects. The study identified significantly lower levels of a specific imaging marker—indicating a loss of dopamine nerve terminal density—across all major regions of the striatum.
The striatum is a critical brain structure responsible for regulating motivation, motor control, and cognitive processing. According to the study, the location of the dopamine loss directly mirrored the specific symptoms reported by patients:
- Ventral striatum: Lower markers in this region were associated with diminished motivation.
- Dorsal putamen: Reductions here correlated with slower physical movement.
- Caudate putamen: Loss in this area was linked to memory difficulties.
Dr. Jeffrey Meyer, senior scientist at the Brain Health Imaging Center and senior author of the study, stated that these findings provide compelling evidence of injury to dopamine-releasing neurons. He noted that such injury is a known factor in other neurological conditions characterized by motor and motivational deficits.
Neuroinflammation as a Primary Driver
This research builds upon previous work by the same team, which established that long COVID patients often exhibit elevated levels of neuroinflammation, particularly in areas rich in dopamine-releasing neurons. Dr. Meyer explained that inflammation can cause direct injury to these neurons. By showing that the decrease in the dopamine marker occurs specifically in these inflamed regions and correlates with patient symptoms, the study creates a clearer link between immune system response and neurological dysfunction.
Clinical Trials for Dopamine Therapy
The identification of dopamine system injury marks a shift in how clinicians may approach long COVID treatment. Historically, research has focused heavily on general immune changes and systemic inflammation.
The study suggests that clinical focus could now shift toward therapeutic strategies aimed at augmenting dopamine function. Potential avenues for future research include the use of dopamine precursors or inhibitors of dopamine metabolism. The research team, in partnership with the University Health Network (UHN), intends to launch a clinical trial within the next few months to test whether targeting the dopamine system can alleviate fatigue, memory issues, and motivational deficits in patients.
Validating the Patient Experience
For those living with the condition, these results offer a biological explanation for symptoms that have often been difficult to categorize. Susan Deuville, a lived experience research adviser who contributed to the work, noted that the findings validate the experiences of patients who have struggled with the persistent and debilitating effects of long COVID for years.
Clinical Implications and Outlook
What is the significance of the striatum in this study? The striatum is a deep-brain structure that acts as a control center for motivation, movement, and cognitive function. The study suggests that damage to the dopamine neurons within this area is a primary driver of the neurological symptoms seen in long COVID.
Does this mean long COVID is a dopamine deficiency disorder? The study indicates that long COVID involves, at least in part, a disorder of the brain’s dopamine system. The researchers propose that the loss of these neurons contributes to the specific neuro-cognitive symptoms patients experience.
Are there approved treatments based on this discovery? No. While the study suggests that repurposing medications that boost dopamine function could be a viable strategy, clinical trials are required to determine the safety and efficacy of these treatments for long COVID patients. The team at CAMH and UHN plans to initiate such trials shortly.