what is lyme disease?
Lyme disease is an infection caused by a bacterium called Borrelia burgdorferi. It gets into the human body through the bite of an infected tick, specifically a type of small tick found in woodland and grassland areas.
You may have heard about the circular, bullseye-shaped rash that can appear after a tick bite. This is one of the most recognisable early signs of Lyme disease, though not everyone who is infected will develop it.
For most people, Lyme disease stays in the skin and joints, causing flu-like symptoms and sometimes joint pain. But in around one in ten untreated cases, the bacterium finds its way into the nervous system: the brain, spinal cord, and the nerves running throughout the body. When this happens, it's called neurological Lyme disease, or Lyme neuroborreliosis.
what makes borrelia unusual?
Borrelia burgdorferi is not your average bacterium. It has evolved over millions of years to be extremely good at surviving inside the bodies of mammals, including humans.
One of its most remarkable tricks is the ability to constantly change the proteins on its outer surface, a bit like changing your coat every time the police are looking for you. This means that by the time your immune system makes antibodies to recognise and attack it, the bacterium has already changed its appearance.
It can also hide inside cells and in the thick, collagen-rich tissue around joints and tendons, places that antibiotics and immune cells struggle to reach in high enough concentrations.
This is not a design flaw. It's what the bacterium has been refining for a very long time. Understanding these tricks is essential to understanding both why the infection can be difficult to treat, and why some people remain unwell for a long time.
disrupting the nervous system
Getting past the brain's defences
Your brain has a remarkable protective barrier called the blood-brain barrier, which acts like a very strict border control, keeping harmful substances out of the brain while letting in what it needs.
Borrelia burgdorferi has the ability to push through this barrier and enter the fluid and tissue surrounding the brain and spinal cord. Once inside, the immune system detects the intruder and mounts a response, sending in immune cells and triggering inflammation.
This inflammation is largely what causes the symptoms of neurological Lyme disease. It's the body trying to fight back, but in doing so it also disrupts normal brain and nerve function.
Direct damage to nerves
The bacterium can also directly infect the cells that wrap around and protect your nerves, a bit like damaging the insulation on an electrical cable. When this insulation (called myelin) is disrupted, the nerves can no longer carry signals properly, which is why many people with neurological Lyme disease experience pain, numbness, tingling, or muscle weakness.
When the immune system mistakes the body for the enemy
One of the more troubling aspects of Lyme disease is what's sometimes called molecular mimicry.
The proteins on the surface of the Borrelia bacterium look remarkably similar to some of the proteins found in human tissue, particularly in joints and, possibly, in some parts of the nervous system.
The immune system, which has been trained to attack those bacterial proteins, can sometimes get confused and start attacking the body's own tissue instead.
This is thought to contribute to why some people continue to have symptoms even after the infection has been treated, because the immune system has essentially been misdirected and hasn't stopped fighting.
what are the symptoms?
The symptoms of neurological Lyme disease can vary a lot from person to person, which is one of the reasons it can be tricky to diagnose.
One of the most common signs is a weakness or drooping on one side of the face, identical in appearance to Bell's palsy, caused by inflammation of the facial nerve. In areas where Lyme disease is common, a child or adult presenting with facial palsy should always be checked for Lyme disease.
Severe, burning nerve pain, often worse at night, is another hallmark. People describe it as shooting, electric, or like being stung repeatedly. It can affect any part of the body depending on which nerves are inflamed.
Headache, neck stiffness, and sensitivity to light are also common, signs of inflammation around the brain and spinal cord. And some people experience what they describe as 'brain fog': difficulty concentrating, word-finding problems, and memory lapses that can be disabling in their own right.
what about chronic lyme?
This is one of the most debated and important questions in Lyme disease research right now.
It's estimated that around 10% to 35% of those treated for Lyme Disease continue to experience symptoms such as fatigue, cognitive difficulties, and pain for months or years after completing antibiotic treatment. This is often called Post-Treatment Lyme Disease Syndrome, or PTLDS.
It's real, and it can be genuinely disabling. What's less clear is exactly why it happens. Several possibilities are being explored.
In some people, the immune system may have been pushed into a state of chronic low-grade inflammation that doesn't fully resolve. In others, the initial infection may have caused some lasting nerve damage that heals slowly. In some cases, it may be a combination of both.
What the evidence does not support is the idea that PTLDS is caused by ongoing active infection. Multiple trials of prolonged antibiotics have not shown benefit, and have the potential to cause harm. This points researchers away from the bacterium itself and towards the immune system and nervous system as the focus for new treatments.
current research
Better tests for neurological involvement
Current blood tests for Lyme disease can miss the infection, especially in its early stages. Researchers are working on tests that look for specific markers of immune response in the fluid surrounding the brain and spinal cord, which would give a much clearer picture of whether the nervous system is affected.
Understanding PTLDS
Large, carefully designed studies are now looking at the immune profiles of people with PTLDS, trying to identify what's different about them biologically, and whether specific anti-inflammatory or immune-modulating treatments might help.
A Lyme vaccine
mRNA vaccine technology, the same approach used in some COVID-19 vaccines, is now being applied to Lyme disease. Early results from clinical trials are encouraging, and a vaccine could eventually prevent the infection altogether, eliminating neurological Lyme disease before it starts.
lyme co-infections
A tick bite can sometimes transmit more than one infection. When Lyme disease occurs alongside another tick-borne infection, this is known as a coinfection. Coinfections can produce overlapping or more severe symptoms and may make diagnosis and treatment more complicated.
Babesia
Babesia is a parasite that infects red blood cells and causes babesiosis. Neurological symptoms associated with Babesia may include persistent or severe headaches, dizziness or light-headedness, confusion or difficulty thinking clearly, problems with concentration and memory, extreme fatigue and reduced mental energy, weakness or difficulties with coordination, balance or walking difficulties, and changes in mental state.
Rickettsia
Rickettsia refers to a group of bacteria that can cause several tick-borne illnesses, depending on the species and geographical location. Neurological symptoms associated with Rickettsia infections may include persistent or severe headaches, dizziness, confusion or difficulty thinking clearly, problems with concentration and memory, extreme fatigue, sensitivity to light, weakness, muscle aches, changes in mental state, and difficulties with balance or coordination
Bartonella
Bartonella is a group of bacteria associated with several human infections. Although Bartonella infection is sometimes discussed in relation to Lyme disease, ther routes of transmission are recognised for some Bartonella species.
Possible neurological manifestations include dizziness or vertigo, numbness, tingling or altered sensation, nerve pain or burning sensations, weakness or muscle pain, tremor or involuntary movements, poor coordination or balance problems, visual disturbances and cognitive difficulties.
Determining root cause
Because symptoms can overlap, a history of tick exposure, travel, geographical location, clinical presentation and appropriate laboratory testing including Armin labs or Igenex testing are essential when considering possible coinfections.
Not everyone with Lyme disease has a coinfection, and persistent symptoms do not automatically mean that another infection is present.
