Lyme Disease or Dementia? A Case of Reversible Cognitive Decline

Cognitive decline may not be dementia
Behavioral changes can have medical causes
Lyme disease can affect the brain
Some cases may be reversible

Lyme disease or dementia? In some cases, symptoms that resemble dementia—such as confusion, hallucinations, and behavioral changes—may be linked to underlying infection.

The authors describe a case in which a 75-year-old man with suspected dementia was referred to an Alzheimer’s Disease Care Unit but later tested positive for Lyme disease.

He initially presented with mild memory loss but was admitted due to hallucinations, confusion, and aggressive behavior.

Two weeks earlier, he had been diagnosed with cognitive impairment compatible with degenerative disease, the authors explain.

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When Symptoms Don’t Fit Typical Dementia

Antipsychotic medications did not alleviate his symptoms, and he was referred to an Alzheimer’s unit.

On admission, he exhibited:

• Delusions and hallucinations
• Aggressive behavior
• Urinary incontinence
• Insomnia

“He started presenting with hallucinations and aggressive behavior, requiring antipsychotic therapy and physical restraints.”

These symptoms developed rapidly—an important distinction from typical neurodegenerative dementia.

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Clues Suggesting an Underlying Infection

One month before his neuropsychiatric symptoms began, the patient developed knee pain that migrated to other joints.

He also reported a tick bite approximately six months earlier.

According to his wife, he had only mild memory issues previously and no confusion, aggression, or behavioral changes.

A CT scan was negative, but blood tests showed elevated inflammatory markers.

This combination—joint symptoms, inflammation, and rapid cognitive decline—raised concern for an infectious cause.

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Diagnosis: Lyme Disease

Because of the joint symptoms, Lyme disease testing was performed and returned positive.

Antibiotic treatment was initiated with intravenous ceftriaxone, followed by doxycycline.

A low-dose steroid was used to manage arthritis symptoms, and antipsychotic medication was eventually discontinued.

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Response to Treatment

Most of the patient’s symptoms improved following treatment for Lyme disease.

However, some deficits persisted:

• Memory loss
• Executive dysfunction

This suggests that while some effects may be reversible, others may take longer to recover or remain partially persistent.

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Why This Case Matters

“Cognitive impairment is usually seen as progressive, but a significant proportion of cases may be reversible,” the authors note.

They emphasize that sudden cognitive decline, especially with behavioral changes, should prompt evaluation for:

• Infections (including Lyme disease)
• Inflammatory conditions
• Other neurologic disorders

Not all dementia-like presentations are neurodegenerative.

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Clinical Perspective

Cases like this highlight the importance of considering reversible causes of cognitive decline.

When symptoms appear suddenly, fluctuate, or are accompanied by systemic findings—such as joint pain or inflammation—clinicians should broaden the differential diagnosis.

For more on cognitive symptoms, see Lyme disease symptoms guide.

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Clinical Takeaway

Lyme disease can present with symptoms that mimic dementia, particularly when the nervous system is involved.

Rapid onset, behavioral changes, and systemic symptoms should prompt evaluation for potentially reversible causes—including infection.

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Dr. Daniel Cameron, MD, MPH
Lyme disease clinician with over 30 years of experience and past president of ILADS.

Symptoms • Testing • Coinfections • Recovery • Pediatric • Prevention