Persistent high fever suggests coinfection more than isolated Lyme
Pathophysiology
Staging model
Early localized infection
Spirochete proliferation at bite site
Erythema migrans as inflammatory response
Early disseminated infection
Hematogenous spread
Neural and cardiac tissue involvement
Late infection
Immune-mediated synovitis
Persistent inflammation after bacterial clearance in some patients
Symptom mechanisms
Carditis
Inflammation of conduction system
Fluctuating AV block severity
Neuroborreliosis
Lymphocytic meningitis
Cranial neuritis and radiculitis patterns
Therapeutic Considerations
Antibiotic principles
Early therapy benefit
Reduced progression to disseminated disease
Reduced duration of symptoms
Route selection by syndrome
Oral therapy for uncomplicated early localized disease
IV therapy for severe carditis and neuroborreliosis
Duration principles
Shorter regimens effective for erythema migrans
Longer regimens for arthritis due to tissue penetration and inflammatory burden
Post-treatment symptoms
Persistent fatigue and pain after treatment can occur
Not an indication for indefinite antibiotics
Functional support and follow-up planning
Jarisch-Herxheimer-like reactions
Transient symptom worsening after antibiotics
Supportive care and reassurance when mild
Patient Discharge Instructions
copy discharge instructions
Discharge plan for suspected or confirmed Lyme disease
Antibiotics
Take exactly as prescribed
Do not stop early even if improved
Symptom expectations
Fever and aches should improve over several days
Rash may take longer to fade
Tick prevention
Daily skin checks after outdoor exposure
Shower soon after outdoor activity
Permethrin-treated clothing and DEET use per label
Return to ED now for red flags
Fainting or near-fainting
Chest pain or trouble breathing
New palpitations or very slow heart rate symptoms
Severe headache with neck stiffness
Confusion or new weakness
New facial droop or trouble closing an eye
Persistent high fever or shaking chills
Dark urine or yellowing of eyes
Rapidly spreading painful skin redness
Follow-up
Primary care visit within 2 to 3 days if not improving
Cardiology follow-up if any ECG abnormality was found
Neurology follow-up if facial palsy or meningitis symptoms occurred
References
Guidelines and high-quality sources
Core guideline set
IDSA AAN ACR 2020 Lyme disease clinical practice guideline
Erythema migrans as clinical diagnosis and immediate treatment recommendation
Antibiotic selection and duration recommendations by syndrome
CDC Lyme disease clinical resources
Two-tier testing principles and timing limitations
Tick removal and prophylaxis criteria summary
Public Health Agency of Canada Lyme disease resources
Canadian endemic region framing and prevention guidance
Testing and reporting considerations
Evidence levels mapping notes
Many Lyme recommendations derive from infectious diseases society guidance rather than ACEP levels
ACEP Level C alignment used for ED-practice consensus items
Class I or IIa framing reserved for pacing and unstable bradycardia pathways consistent with cardiology standards
Cardiac conduction management references
ACC AHA bradycardia and pacing guideline principles for unstable high-grade AV block
Telemetry and temporary pacing for symptomatic high-grade block
Diagnostic performance and pitfalls references
Two-tier serology sensitivity is lower in early localized infection
False negative risk in first weeks
Improved sensitivity later in disease
IgM false positives increase outside early window
Avoid isolated IgM interpretation without compatible timing
Correlate with exposure and syndrome
SymptomDx is an educational tool for medical professionals. It does not replace clinical judgment. Verify all clinical data and drug dosages with authoritative sources.