Lyme endocarditis diagnosed by PCR testing

When Stroke Symptoms Lead to Unexpected Diagnosis

A 40-year-old man presented to the emergency department with a headache that had been ongoing for 5 days and intermittent numbness in his left arm.

CT scan and MRI of the brain revealed acute subarachnoid hemorrhage and the patient was admitted to the neurology unit for medical management of acute stroke.

Additional testing “redemonstrated the previously seen density on the mitral valve in addition to perforation of the valve leaflet with 4+ mitral regurgitation,” the authors state.

The clinical picture was evolving: what began as neurologic emergency revealed underlying cardiac pathology. The valve perforation and severe regurgitation indicated infective endocarditis—infection of the heart valve.

Culture-Negative Endocarditis Requires Tissue PCR

“We present a new case of culture-negative Lyme endocarditis highlighting clinical characteristics that should trigger tissue PCR to diagnose this pathogen in cases of culture-negative endocarditis,” the authors state.

The patient underwent a median sternotomy with cardioplegic arrest for aortic valve replacement and mitral valve repair.

Given the patient’s exposure to cats and farm animals and his squirrel-hunting history, he was tested for Coxiella and Bartonella—organisms that cause culture-negative endocarditis in patients with animal exposure.

Blood cultures were negative. Standard microbiologic culture techniques failed to identify the causative organism. This is not unusual—up to 31% of endocarditis cases are culture-negative, often due to prior antibiotic exposure, fastidious organisms with special growth requirements, or non-bacterial pathogens.

PCR Testing Reveals Borrelia burgdorferi

One week after the patient’s discharge from the hospital, PCR testing from mitral valve tissue returned positive for Borrelia burgdorferi.

The patient was treated successfully with doxycycline.

This represents a critical diagnostic breakthrough. Standard blood cultures cannot grow Borrelia burgdorferi—the organism requires specialized culture media and conditions rarely available in clinical laboratories. Without tissue PCR testing, the etiology would have remained unknown, and targeted antimicrobial therapy impossible.

PCR (polymerase chain reaction) detects bacterial DNA directly in tissue samples. It doesn’t require viable organisms or successful culture. In culture-negative endocarditis, tissue PCR from excised valve material can identify pathogens that standard techniques miss.

Missed Opportunities for Earlier Diagnosis

There was initially a low suspicion for Lyme endocarditis because of the lack of previous erythema migrans or recollection of recent contact with ticks.

“Convalescent serology was never rechecked 3 weeks after this initial presentation, and consequently he went undiagnosed, allowing for late complications to arise that may have been avoided with follow-up titers,” the authors point out.

This statement suggests the patient may have presented with earlier symptoms that were evaluated but not followed up appropriately. Initial Lyme serology in early infection is often negative—antibodies haven’t developed yet. Convalescent serology performed 3-6 weeks later captures seroconversion that initial testing misses.

Without follow-up serology, early Lyme disease went undiagnosed. The infection progressed untreated, ultimately causing endocarditis—a rare but devastating complication. Valve destruction led to severe mitral regurgitation. Embolic events from infected valve vegetation caused stroke.

The clinical cascade could have been prevented: early recognition → antibiotic treatment → preventing progression to cardiac involvement → avoiding valve surgery and stroke.

Clinical Characteristics Triggering PCR Testing

The authors conclude it is imperative to be aware that Borrelia species are a documented cause of infective endocarditis.

It is important to keep this rare causative organism in the differential diagnosis in cases of culture-negative endocarditis when the valve pathology suggests an unusual pattern and it is critical to send tissue for PCR to confirm the diagnosis.

Specific characteristics in this case that should have triggered Lyme consideration: Culture-negative endocarditis despite adequate culture techniques. Geographic location where Lyme disease is endemic. Outdoor exposure history (squirrel hunting). Unusual valve pathology with perforation. Young patient without typical endocarditis risk factors (IV drug use, prosthetic valves, prior endocarditis).

When these features converge—particularly culture-negative endocarditis in endemic area with outdoor exposure—tissue PCR for Borrelia should be performed routinely rather than as afterthought.

Why Lyme Endocarditis Is Missed

Lyme endocarditis is rare, accounting for a tiny fraction of endocarditis cases. Most clinicians never see a case, making it easy to overlook in differential diagnosis.

The absence of classic Lyme features—erythema migrans rash, recalled tick bite—reduces suspicion further. However, many patients never notice tick bites. Nymphal Ixodes ticks are tiny (poppy seed size) and painless. EM rash occurs in only 70-80% of cases and may appear in locations patients don’t see (back, scalp).

Additionally, Lyme carditis typically manifests as conduction abnormalities (heart block) rather than endocarditis. Valve infection is extremely unusual, making clinicians less likely to consider Lyme when endocarditis presents.

Finally, Borrelia doesn’t grow in standard blood cultures. Without specific tissue PCR testing, diagnosis is impossible. Culture-negative endocarditis has many causes—Coxiella, Bartonella, Brucella, fungi, Tropheryma whipplei. Lyme is rarely included in the differential.

Treatment and Outcomes

The patient was treated successfully with doxycycline following PCR confirmation of Lyme endocarditis.

This represents appropriate antibiotic selection. Doxycycline penetrates tissues well and has excellent activity against Borrelia burgdorferi. For Lyme endocarditis, treatment typically requires 4-6 weeks of doxycycline or intravenous ceftriaxone.

The patient also underwent valve replacement and repair—surgical intervention necessary because infection had already destroyed valve tissue. Medical therapy alone cannot reverse structural damage. Without surgery, ongoing severe mitral regurgitation would cause progressive heart failure.

The successful outcome—cardiac surgery followed by targeted antibiotic therapy—demonstrates that even late-stage Lyme complications can be treated when diagnosis is established.

Frequently Asked Questions

Can Lyme disease cause endocarditis?
Yes, though it’s extremely rare. Borrelia burgdorferi can infect heart valves, causing culture-negative endocarditis. This case demonstrates Lyme endocarditis causing valve perforation, severe regurgitation, and embolic stroke.

How is Lyme endocarditis diagnosed?
PCR testing of heart valve tissue obtained during surgery. Blood cultures are negative because Borrelia doesn’t grow in standard culture media. Standard serology may be negative or inconclusive. Tissue PCR provides definitive diagnosis.

Why wasn’t Lyme suspected earlier in this case?
No recalled tick bite or erythema migrans rash. Convalescent serology was never rechecked after initial presentation, missing opportunity for early diagnosis. Lyme endocarditis is rare, making it easy to overlook in culture-negative cases.

What are signs of culture-negative endocarditis from Lyme?
Valve dysfunction or perforation with negative blood cultures, unusual valve pathology, young patient without typical endocarditis risk factors, outdoor exposure in endemic area, neurologic or embolic complications.

Should all culture-negative endocarditis be tested for Lyme?
In endemic areas with compatible exposure history and unusual valve pathology, yes. Tissue PCR for Borrelia should be routine in culture-negative endocarditis when clinical features suggest possible Lyme disease.

Clinical Takeaway

This case illustrates why tissue PCR testing is critical in culture-negative endocarditis and how missed opportunities for earlier Lyme diagnosis can lead to devastating cardiac complications. A 40-year-old man presented with headache and left arm numbness. Brain imaging revealed acute subarachnoid hemorrhage—stroke from embolic event. Further evaluation showed valve perforation with severe mitral regurgitation—infective endocarditis. Blood cultures were negative. Given animal exposure history, testing focused on Coxiella and Bartonella. The patient underwent cardiac surgery with valve replacement and repair. One week post-discharge, PCR testing from mitral valve tissue returned positive for Borrelia burgdorferi. This was Lyme endocarditis—an extremely rare complication that standard diagnostic approaches missed. The diagnosis came only because tissue was sent for PCR testing. Without it, the etiology would have remained unknown forever. Standard blood cultures cannot grow Borrelia burgdorferi. The organism requires specialized media and conditions rarely available clinically. PCR detects bacterial DNA directly in tissue without requiring viable organisms or successful culture. In culture-negative endocarditis, it’s the only way to identify Lyme disease. The missed opportunities are striking. The patient lacked recalled tick bite or erythema migrans rash—but many Lyme patients never notice tiny nymphal tick bites, and EM rash occurs in only 70-80% of cases. More significantly, convalescent serology was never rechecked after initial presentation. Early Lyme serology is often negative because antibodies haven’t developed. Convalescent serology 3-6 weeks later captures seroconversion that initial testing misses. Without follow-up, early Lyme went undiagnosed. Untreated infection progressed to endocarditis—preventable with early recognition and antibiotic therapy. Valve destruction caused severe regurgitation. Infected vegetation embolized to brain causing stroke. The cascade could have been prevented: early diagnosis → treatment → avoiding cardiac complications → preventing surgery and stroke. The authors conclude that Borrelia species must be considered in culture-negative endocarditis differential diagnosis, particularly when valve pathology is unusual and patient has endemic area exposure. Tissue PCR should be routine rather than afterthought. Specific triggers for Lyme consideration: culture-negative despite adequate techniques, endemic geographic location, outdoor exposure history, unusual valve pathology with perforation, young patient without typical endocarditis risk factors. When these converge, tissue PCR for Borrelia should be performed automatically. The successful treatment with doxycycline following PCR confirmation demonstrates that even late-stage Lyme complications respond to appropriate antimicrobial therapy when diagnosis is established—albeit requiring cardiac surgery to repair damage that early treatment would have prevented.