Nervous system involvement in Lyme disease

The blood-brain barrier regulates what enters the brain and spinal cord. Borrelia burgdorferi has been shown in research to actively cross this barrier — it binds to and penetrates the endothelial cells that form the barrier wall. Once inside, it gains access to the central nervous system, where standard antibiotics penetrate poorly and the immune response is limited.

Borrelia has been detected in brain tissue, spinal cord, and peripheral nerves in post-mortem studies. It can invade neurons, glial cells, and the dorsal root ganglia — clusters of sensory nerve cell bodies that relay pain and sensation signals. Invasion of the dorsal root ganglia is the primary mechanism behind radicular pain and sensory neuropathy.

Even when Borrelia is not directly present in nerve tissue, the immune response it generates is itself neurotoxic. Elevated inflammatory cytokines disrupt nerve signalling, damage myelin (the protective coating on nerve fibres), and create conditions in which nerves fire abnormally. This produces symptoms even in the absence of structural damage that would be visible on imaging.

Some research suggests that antibodies the immune system produces against Borrelia proteins cross-react with nerve tissue proteins that share similar molecular sequences. In this autoimmune mechanism, the immune system’s own response attacks the nervous system — which may explain why some neurological symptoms persist even after bacterial load has been reduced by antibiotic treatment.

Research found it took an average of eighteen months after infection for peripheral nervous system symptoms to manifest, and two years for central nervous system symptoms to appear. This delay is clinically important: by the time neurological symptoms become prominent, the tick bite may be long forgotten, and the connection between infection and neurological decline is rarely made.

Borrelia can form biofilms — communities of bacteria enclosed in a protective matrix that resists antibiotics and immune clearance — in nervous system tissue. Research by Alan MacDonald and others has detected Borrelia biofilms in brain tissue of patients with Alzheimer’s disease. In biofilm form, the bacteria can remain dormant before reactivating, which may explain the relapsing-remitting course seen in some patients.

The most common form in late Lyme disease. Multiple nerves are affected, typically starting distally — in the hands and feet — and progressing proximally over time. Symptoms are often symmetric: both hands, or both feet, affected in a similar pattern. Patients describe numbness, tingling, burning, or a “glove and stocking” sensory loss. Standard nerve conduction studies may show mild slowing, but negative results do not rule out neuropathy — particularly in small fiber involvement, where standard testing is unreliable.

Nerve root inflammation is one of the classic presentations of Lyme neuroborreliosis, particularly in European strains (Bannwarth’s syndrome). Pain radiates from the spine along the path of an affected nerve root — into the arm, the leg, the chest, or the abdomen. It is typically worse at night, described as sharp, jabbing, deep and boring, or electric. It is frequently misidentified as a herniated disc, intercostal neuralgia, or unexplained abdominal pain.

A pattern in which multiple individual peripheral nerves are affected, but in an asymmetric and sometimes seemingly random distribution — one hand, one foot, one facial area. Research suggests that virtually all Lyme-related peripheral neuropathies are manifestations of this underlying pattern. It results from inflammatory vasculitis (blood vessel inflammation) that Borrelia produces around nerve sheaths, cutting off the blood supply to individual nerve segments.

Burning in the feet, particularly at night. Hypersensitivity to touch — clothing feels painful, or walking on a hard floor creates an intense unpleasant sensation. Temperature dysregulation — feeling that one part of the body is hot when it is not, or cold intolerance far beyond what the room temperature explains. Prickling, crawling skin sensations. These symptoms tend to be worst at night and often worsen during herxheimer reactions.

Small fibers also carry signals that regulate automatic body functions — heart rate, blood pressure, digestion, sweating, and bladder control. When damaged, autonomic dysregulation follows: postural dizziness when standing, abnormal sweating, heart rate fluctuations, digestive motility problems, and bladder urgency. SFN therefore bridges the neurological and autonomic symptom clusters and may be a central mechanism in dysautonomia seen in Lyme patients.

Facial nerve palsy produces weakness or complete paralysis of the muscles on one side of the face: the eye may not fully close, the corner of the mouth droops, and the ability to raise an eyebrow on the affected side is lost. In Lyme disease, it is often bilateral — affecting both sides, sometimes not simultaneously. Bilateral Bell’s palsy is rare in other conditions and should be considered a red flag for Lyme neuroborreliosis. CDC reporting data show facial palsy in 9 out of every 100 reported Lyme cases.

Lyme can affect cranial nerve VIII (vestibulocochlear) — producing tinnitus, hearing loss, or vestibular disturbance. Cranial nerve VI (abducens) — causing double vision or inability to move the eye fully laterally. Cranial nerve II (optic nerve) — producing visual changes, light sensitivity, or optic neuritis. Cranial nerve X (vagus) — with effects on heart rate, digestion, and swallowing. Any cranial neuropathy without a clearly established cause warrants investigation for tick-borne illness.

The trigeminal nerve can be directly invaded by Borrelia or inflamed by the immune response to infection. Inflammation of the trigeminal nerve root or ganglion produces exactly the kind of episodic, severe, lancinating facial pain seen in classical trigeminal neuralgia. In Lyme patients, this pain may be accompanied by other cranial nerve signs, or may appear in isolation. Pain neurology literature identifies Lyme as a rule-out diagnosis in any atypical facial pain or neuralgia syndrome.

Standard brain MRI looks for vascular compression of the trigeminal root. When no compression is found, the neuralgia is labelled idiopathic and managed symptomatically — anticonvulsants like carbamazepine suppress the pain signal. These medications may reduce the symptom but do nothing to address an underlying infection. In Lyme-related trigeminal neuralgia, the pain is driven by an active infectious process; suppressing the nerve signal while leaving the infection untreated allows neurological damage to progress.

Brain fog is not a vague complaint. It is a clinical state characterised by slowed processing speed, impaired working memory, difficulty with word retrieval, inability to sustain attention, and a feeling of cognitive unreliability. Neuropsychological testing in Lyme patients with encephalopathy has consistently shown measurable deficits in these areas, even when structural MRI appears normal. The mechanism involves cytokine-mediated disruption of neuronal signalling, reduced cerebral blood flow in affected areas, and in some cases direct bacterial invasion of brain tissue.

Brain MRI in Lyme encephalopathy frequently shows no abnormality on standard sequences — which is why patients are told there is nothing wrong. However, SPECT (single-photon emission computed tomography) imaging measures blood flow rather than structure. Research at Johns Hopkins using SPECT in Lyme patients revealed hypoperfusion — areas of reduced blood flow — in a pattern distinct from other neurological conditions, correlating with patients’ reported cognitive symptoms. SPECT is not a routine scan and is not available in most standard neurology practices.

Cerebrospinal fluid analysis in Lyme neuroborreliosis may show elevated protein, elevated white blood cells, and — critically — oligoclonal bands, which are immunoglobulin patterns associated with CNS inflammation and considered a hallmark of multiple sclerosis. Their presence in Lyme patients has led directly to misdiagnosis of MS. Research published in PLOS One demonstrated that oligoclonal bands in Lyme neuroborreliosis are in fact borrelia-specific — targeted against the infecting bacterium — rather than the self-reactive antibodies of MS. In MS, oligoclonal bands persist indefinitely. In Lyme, they disappear with successful treatment.

Non-restorative sleep is one of the most consistent and debilitating features of Lyme encephalopathy. It is not simply insomnia — it is structural. Sleep studies in Lyme patients show disruption of deep slow-wave sleep: the stage during which neurological repair, glymphatic clearance (the brain’s waste-removal system), and memory consolidation occur. When this stage is impaired, cognitive dysfunction worsens, immune function is suppressed, and inflammatory burden increases — creating a self-perpetuating loop.

Both can produce white matter lesions (T2 hyperintensities) on brain MRI. Both can produce oligoclonal bands in CSF. Both can produce relapsing-remitting episodes of neurological symptoms separated by periods of partial or complete remission. Both can affect vision, balance, sensation, bladder function, and cognition. A patient with these features who tests seronegative on standard Lyme testing may receive an MS diagnosis by exclusion.

MS lesions have characteristic locations (periventricular, juxtacortical, infratentorial, spinal cord) following McDonald criteria; Lyme lesions are less constrained and often smaller. MS oligoclonal bands persist indefinitely; Lyme oligoclonal bands are borrelia-specific and clear with treatment. MS is not associated with the radiculopathy, marked joint involvement, autonomic dysfunction, or geographic and tick-exposure clustering that Lyme produces. Bilateral Bell’s palsy and the typical Bannwarth radicular pain pattern are not features of MS.

The connection between spirochetal infection and dementia was established long before the Lyme hypothesis. Treponema pallidum — the spirochete that causes syphilis — is a well-documented cause of dementia in its late stage. Late-stage syphilis (general paresis) produces brain atrophy, cognitive decline, amyloid deposition, and neurofibrillary tangles — the same pathological features that define Alzheimer’s disease. Dr. Judith Miklossy, Swiss neuropathologist and Director of the Prevention Alzheimer International Foundation, has argued that Borrelia burgdorferi may operate in an analogous way.

In 1986, Dr. Alan MacDonald first reported the presence of Borrelia burgdorferi in the brain tissue of an Alzheimer’s patient. Miklossy’s research, published in the Journal of Alzheimer’s Disease in 2004, confirmed the presence of Borrelia antigens and genes co-localised with beta-amyloid deposits in Alzheimer’s brain tissue. A 2022 study by Senejani et al. in the same journal found Borrelia co-localising with amyloid and phosphorylated tau — the two pathological hallmarks of Alzheimer’s — in post-mortem brain tissue from both Alzheimer’s and Parkinson’s patients.

A central pillar of Alzheimer’s research has been the amyloid hypothesis — the idea that accumulation of beta-amyloid protein is the primary cause of neurodegeneration. This hypothesis has struggled: dozens of clinical trials targeting amyloid have largely failed to produce the cognitive improvements predicted. An alternative view, supported by MacDonald’s and Miklossy’s work, is that amyloid accumulation may be a downstream consequence of chronic infection — the brain’s attempt to trap and neutralise bacteria. In this model, amyloid is not the disease; it is the scar tissue of a persistent infectious process. If this model is correct, treating infection early may prevent the downstream accumulation.

Miklossy’s 2011 review in the Journal of Neuroinflammation — “Alzheimer’s disease: a neurospirochetosis” — analysed all available data from 247 examined cases. The analysis found a statistically significant association between spirochetes and Alzheimer’s (p = 1.5 × 10¹&sup7;, odds ratio = 20). When techniques detecting all types of spirochetes were used, spirochetal infection was observed in more than 90% of Alzheimer’s brain tissue. Borrelia burgdorferi specifically was detected in 25.3% of Alzheimer’s cases — thirteen times more frequently than in controls.

Miklossy et al.’s 2006 study in Neurobiology of Aging exposed primary mammalian neuronal and glial cells to Borrelia spirochetes in culture. The result: elevated amyloid precursor protein levels, beta-amyloid deposition, tau hyperphosphorylation, and structures morphologically identical to Alzheimer’s senile plaques and neurofibrillary tangles — none of which were observed in uninfected control cultures. This is not an association study. The spirochetes directly produced Alzheimer’s pathology in otherwise healthy brain cells.

The research connection between Borrelia and Parkinson’s is less developed but documented. The 2022 Senejani study found Borrelia antigens and DNA in brain tissue from Parkinson’s patients, co-localising with amyloid and tau markers. Separately, Lyme disease can produce a syndrome clinically mimicking Parkinson’s: tremor, rigidity, bradykinesia (slowness of movement), and gait disturbances. There are peer-reviewed case reports of Parkinson’s-like syndromes reversing or substantially improving with Lyme treatment when the underlying infection is identified.

Bartonella infection is associated with a neuropsychiatric profile that is strikingly distinct from Borrelia: agitation, sudden severe anxiety, mood instability, rage or emotional dysregulation that feels out of character, and in some cases presentations that resemble bipolar disorder, psychosis, or personality change. These effects are believed to be driven by Bartonella’s invasion of the brain’s vascular supply, triggering neuroinflammation in limbic and prefrontal regions.

Bartonella produces the characteristic stretch-mark-like striae seen on the skin (described in the dermatological cluster) through vascular inflammation. It produces similar inflammation in the vascular supply to peripheral nerves, contributing a neuropathy that compounds Borrelia’s direct nerve damage. Some researchers describe Bartonella as producing more severe and rapid-onset neurological involvement than Borrelia alone, particularly in the central nervous system.

Standard MRI detects structural changes: lesions, tissue destruction, mass effects. Neurological Lyme is predominantly a functional disruption — inflammation that alters how nerves signal without destroying visible tissue. SPECT imaging, which measures blood flow rather than structure, is more likely to show abnormalities in Lyme encephalopathy. However, SPECT is not a routine scan and is not available in most standard neurology practices.

The standard two-tier test measures the antibody response to Borrelia — it does not detect the bacteria directly. In people who are immunosuppressed, or whose infection has been partially treated, or in whom the immune response has not yet fully developed, antibody levels may be too low to trigger a positive result. Studies suggest the two-tier test has sensitivity of approximately 40–60% in early disease. Late neurological involvement is precisely the stage at which false negatives remain common.