When Tick Disease Attacks the Brain: CNS Vasculitis from Ehrlichia canis in a Dog
A case report highlighting an uncommon neurological presentation of ehrlichiosis—and why early recognition matters
We all know ehrlichiosis as a tick-borne disease that typically presents with fever, thrombocytopenia, and maybe some nonspecific lethargy. But a fascinating case report published in Veterinary Medicine and Science reminds us that Ehrlichia canis can do something far more dramatic: trigger severe central nervous system vasculitis that mimics other serious neurological conditions.
Miguel Benito Benito and colleagues describe a 4-year-old spayed mixed-breed dog with a 2-month history of intermittent vestibulo-cerebellar ataxia and right head tilt—clinical signs that could fit dozens of differential diagnoses. What makes this case worth discussing is both the striking MRI findings and the remarkable response to targeted antibiotic therapy, offering important lessons for recognizing and treating this uncommon manifestation of a common disease.
The Clinical Picture
The patient presented with signs compatible with right paradoxical vestibular syndrome—that interesting presentation where central vestibular dysfunction causes a head tilt away from the side of the lesion, contradicting our typical vestibular localization rules. This alone signals a brainstem problem and should raise our index of suspicion for serious pathology.
The intermittent nature of signs over two months is particularly noteworthy. This isn't an acute stroke or rapid-onset inflammatory disease. The waxing and waning course could easily lead us down the wrong diagnostic path, perhaps considering seizure disorders, intermittent vascular events, or slowly progressive inflammatory conditions.
The Bloodwork Clues
Here's where things get interesting. The CBC revealed findings that should make us think beyond primary neurological disease:
Moderate lymphocytosis - suggesting immune system activation
Thrombocytopenia - a classic hallmark of ehrlichiosis that we see in most cases
Hyperproteinemia with hyperglobulinemia - indicating chronic antigenic stimulation
In isolation, none of these findings scream "neurological disease." But when combined with vestibular signs, they should prompt us to consider systemic infectious or inflammatory processes that can have CNS manifestations. This is exactly the kind of pattern recognition that separates complete diagnostic workups from focused investigations.
The thrombocytopenia is particularly significant here. While we often see low platelets with tick-borne diseases, when it appears alongside neurological signs, we need to consider both direct CNS infection and immune-mediated complications, including vasculitis.
The Imaging: When MRI Tells the Story
The MRI findings were dramatic and helped narrow the differential diagnosis considerably:
Multiple bilateral ill-defined lesions involving white matter of the brainstem, cerebellum, and forebrain
Strong diffuse meningeal contrast enhancement
This pattern is significant. The multifocal, bilateral distribution rules out many focal processes (neoplasia, focal trauma, single infarct). The meningeal enhancement suggests an inflammatory process affecting the meninges and potentially the blood vessels supplying the brain.
White matter predominance with multifocal distribution classically suggests a few key differentials:
Inflammatory/infectious meningoencephalitis
Vasculitis
Demyelinating disease
Certain toxic exposures
The strong meningeal enhancement particularly supports infectious or inflammatory etiologies. In a dog with systemic signs (thrombocytopenia, hyperglobulinemia), tick-borne disease should absolutely be on that list.
CSF Analysis: Confirming Inflammation
Cerebrospinal fluid cytology showed lymphocytic pleocytosis—increased white blood cells with predominantly lymphocytes. This finding confirms that we're dealing with an inflammatory CNS process and helps narrow our differentials further.
Lymphocytic pleocytosis can occur with:
Viral infections
Chronic bacterial infections
Rickettsial diseases (including ehrlichiosis)
Fungal infections
Immune-mediated/sterile inflammatory diseases
Combined with positive Ehrlichia spp. serology, the pieces fall into place: this is CNS involvement from ehrlichiosis, specifically manifesting as vasculitis affecting the cerebral blood vessels.
The Vasculitis Connection
CNS vasculitis from E. canis is uncommon but well-documented. The pathophysiology involves both direct endothelial infection and immune-mediated vascular inflammation. Ehrlichia organisms have tropism for monocytes and endothelial cells, and when they infect CNS vasculature, they can trigger:
Endothelial damage and dysfunction
Immune complex deposition in vessel walls
Inflammatory infiltrates around blood vessels
Subsequent ischemia and tissue damage
This explains the multifocal white matter lesions on MRI—they represent areas of vascular compromise and inflammation. The meningeal enhancement reflects the inflammatory process affecting the meninges and superficial blood vessels.
What makes this case particularly instructive is that it demonstrates how a systemic tick-borne infection can have dramatic CNS manifestations. We tend to think of ehrlichiosis as causing relatively mild, nonspecific illness, but cases like this remind us that serious neurological complications can occur.
Treatment Response: Dramatic and Diagnostic
The patient was treated with doxycycline—the gold standard for ehrlichiosis. The response was remarkable:
Clinical improvement within 24 hours - suggesting we hit the right target
Treatment continued for 6 weeks - appropriate duration for tick-borne disease
Complete resolution of MRI lesions on follow-up imaging
CSF showing only albumin-cytological dissociation (elevated protein without cells—a sign of blood-brain barrier disruption resolving)
Remained asymptomatic three months post-discharge
This dramatic response is both therapeutic and diagnostic. When we see complete resolution of multifocal CNS lesions with antibiotic therapy alone, it strongly supports an infectious etiology. Many of our inflammatory CNS diseases would require immunosuppression and wouldn't resolve completely with antibiotics.
The 24-hour improvement is particularly striking. While we don't expect MRI lesions to resolve that quickly, the clinical response suggests we rapidly interrupted the inflammatory cascade driving the patient's signs.
Clinical Pearls for Practice
This case offers several important takeaways for general practice:
1. Think Systemically with Neurological Cases
When faced with vestibular signs or other neurological presentations, don't just localize and assume primary CNS disease. Look for systemic clues on bloodwork. Thrombocytopenia with neurological signs should prompt consideration of vasculitis, whether immune-mediated or infectious.
2. Ehrlichiosis Can Do This
In endemic areas, E. canis should be on your differential list for inflammatory CNS disease, especially when you see:
Thrombocytopenia
Hyperglobulinemia
Multifocal neurological signs
Positive tick-borne disease serology
3. Paradoxical Vestibular Syndrome Means Central Disease
When you see a head tilt that's "wrong" (tilting away from the side of the lesion), you're dealing with central vestibular dysfunction, likely at the level of the brainstem. This demands more aggressive workup than peripheral vestibular disease.
4. Don't Underestimate the Doxycycline Trial
In cases where advanced imaging isn't available or affordable, a therapeutic trial of doxycycline for suspected tick-borne disease is reasonable when:
You're in an endemic area
Clinical signs fit
Bloodwork shows supportive changes
You've ruled out immediately life-threatening causes
Clinical improvement within days can support your diagnosis, though ideally you'd confirm with serology.
5. Follow-up Imaging Matters
This case beautifully demonstrates the value of repeat MRI after treatment. Complete resolution of lesions confirms effective therapy and helps with long-term prognostication. When possible, documenting resolution also helps justify aggressive treatment to clients who might question extended antibiotic courses.
The Bottom Line
CNS vasculitis from Ehrlichia canis is an uncommon but important manifestation of tick-borne disease that can present with dramatic neurological signs. The key to diagnosis is recognizing the pattern: multifocal CNS signs, thrombocytopenia, hyperglobulinemia, and positive serology in a dog from an endemic area.
The excellent response to doxycycline and complete resolution of lesions seen in this case should encourage us to keep tick-borne disease on our differential lists for inflammatory CNS disease, even when presentations seem unusual. Early recognition and appropriate treatment can lead to complete recovery, making this a condition we definitely don't want to miss.
Full Text Link: Central Nervous System Vasculitis Due to Ehrlichia canis in a Dog - Veterinary Medicine and Science, PMCID: PMC12581152
