One of the most important clues to understanding brain fog in Lyme disease may come from an unexpected source: COVID-19 research.

A study by Remsik and colleagues, published in Cancer Cell, examined 13 patients hospitalized with COVID-19 who developed severe cognitive symptoms — confusion, headaches, memory loss, and in some cases psychosis and seizures. The researchers expected to find evidence of viral infection in the cerebrospinal fluid. They did not.

Instead, they found elevated cytokines — inflammatory signaling molecules — flooding the central nervous system. This finding raises a critical question: could cytokine brain fog explain what Lyme disease patients have been experiencing for decades?

What Are Cytokines?

Cytokines are small proteins released by immune cells to coordinate the body’s inflammatory response. During infection, cytokines help fight off pathogens. But when the immune response becomes prolonged or dysregulated, excessive cytokine activity can damage healthy tissue — including the brain.

This overactivation is sometimes called a “cytokine storm.” When cytokines cross the blood-brain barrier or are produced within the central nervous system, they can disrupt neural communication, alter neurotransmitter function, and impair cognition.

What the COVID-19 Study Found

Remsik and colleagues found persistent inflammation and elevated cytokines in the cerebrospinal fluid of COVID-19 patients with brain fog — despite no evidence of direct viral invasion of the brain.

The authors concluded that these increased cytokines likely resulted from both increased blood-brain barrier permeability and local production by cells within the central nervous system. In other words, the brain fog was driven by inflammation, not by the virus itself.

This distinction matters enormously for Lyme disease patients.

Cytokine Brain Fog and Lyme Disease

Investigators have previously raised concerns that Lyme disease spirochetes can cross the blood-brain barrier, triggering neuroinflammation that contributes to brain fog. Dr. Robert Bransfield raised concerns that persisting immune activation causes a cytokine storm in patients with chronic Lyme disease — a mechanism strikingly similar to what Remsik and colleagues documented in COVID-19.

If cytokines can cause brain fog in COVID-19 patients without direct brain infection, the same mechanism may explain why many Lyme disease patients experience persistent cognitive symptoms even after antibiotic treatment — when the spirochete may no longer be detectable but the inflammatory cascade continues.

This aligns with what clinicians observe in post-treatment Lyme disease syndrome (PTLDS): patients whose infections have been treated but whose immune systems remain activated, producing ongoing symptoms including brain fog, fatigue, and pain.

How Cytokines Affect Brain Function

Elevated cytokines in the central nervous system can disrupt cognition through several mechanisms:

• Impairing communication between neural networks
• Altering neurotransmitter balance, particularly serotonin and dopamine
• Activating microglia — the brain’s immune cells — which can sustain inflammation
• Increasing blood-brain barrier permeability, allowing more inflammatory molecules into the brain
• Disrupting sleep architecture and autonomic nervous system regulation

The result is what patients describe as slowed thinking, difficulty concentrating, word-finding problems, and mental fatigue — the hallmarks of cytokine brain fog.

Why This Research Matters for Lyme Patients

For years, Lyme disease patients reporting persistent brain fog after treatment have been told their symptoms are psychological or stress-related. The cytokine research from COVID-19 provides a biologic framework that validates what these patients have been saying all along: their cognitive symptoms are driven by inflammation, not imagination.

This parallel between COVID-19 and Lyme disease brain fog also opens the door to new treatment strategies targeting neuroinflammation rather than relying solely on antibiotics or psychiatric medications.

Frequently Asked Questions

What is cytokine brain fog?
Cytokine brain fog refers to cognitive impairment caused by elevated inflammatory cytokines in the central nervous system. It can cause slowed thinking, memory problems, and difficulty concentrating.

Can cytokines cause brain fog without active infection?
Yes. The COVID-19 study found elevated cytokines and cognitive symptoms even without direct viral infection of the brain. The same pattern may occur in Lyme disease after spirochetes are no longer detectable.

Is cytokine brain fog the same as Lyme brain fog?
Cytokine-driven inflammation is likely one of the key mechanisms behind brain fog in Lyme disease, though other factors — including autonomic dysfunction, sleep disruption, and co-infections — may also contribute.

Can cytokine brain fog be treated?
Addressing the underlying inflammatory process is key. This may include treating active infections, supporting immune regulation, improving sleep, and reducing neuroinflammatory triggers.

Why do Lyme and COVID brain fog look so similar?
Both conditions can trigger immune activation and cytokine elevation within the central nervous system. The cognitive symptoms are driven by the inflammatory response rather than by the specific pathogen.

References

1. Remsik J, Wilcox JA, Babady NE, et al. Inflammatory Leptomeningeal Cytokines Mediate COVID-19 Neurologic Symptoms in Cancer Patients. Cancer Cell. 2021;39(2):276-283.e3.
2. Bransfield RC. The psychoimmunology of Lyme/tick-borne diseases and its association with neuropsychiatric symptoms. Open Neurol J. 2012;6:88-93.

Related Reading

• Brain Fog Lyme Disease: Why It Happens and What Helps
• Brain Fog in COVID-19 and Lyme Disease Patients
• Cognitive Dysfunction in Lyme Disease
• Disseminated Lyme Disease and Weakened Immune System
• Persistent Lyme Infection or Inflammatory Immune Response?