01Approach to the Critical Patient/attcp50

Immediate priorities

›Lyme carditis recognition

›High-degree AV block with hemodynamic compromise

›Syncope or presyncope in endemic area resident

›PR interval >= 300 ms on ECG

›Complete heart block management

›Transcutaneous pacing on standby

›Transvenous pacing if hemodynamically unstable

›If third-degree AV block with hypotension, activate cardiac team immediately

›Ceftriaxone 2 g IV daily initiated concurrently

›Atropine 0.5 mg IV for symptomatic bradycardia bridge

›Neuroborreliosis threats

›Lyme meningitis with raised ICP features

›Severe headache and meningismus

›Photophobia and vomiting

›Encephalopathy with altered consciousness

›GCS assessment and trend

›If GCS < 13, CT head prior to LP

›If bilateral facial palsy with meningismus, initiate IV ceftriaxone empirically

›Do not delay for serology confirmation

›Neurology consultation

Monitoring and targets

›Cardiac monitoring bundle

›Continuous telemetry for all suspected Lyme carditis

›PR interval trend every 15 to 30 minutes in high-degree block

›AV block can fluctuate from first-degree to complete within minutes

›Serial 12-lead ECGs

›Capture PR prolongation progression

02History/hx76

Presentation pattern

›Erythema migrans history

›Expanding skin lesion at bite site

›Onset 3 to 30 days after tick bite

›Diameter >= 5 cm

›Lesion characteristics

›Homogeneous red patch or target bull's-eye pattern

›Warm to touch but rarely pruritic or painful

›Multiple EM lesions suggest early dissemination

›Lesions at sites distant from bite

›Hematogenous spread marker

Tick exposure history

›Exposure details

›Geographic risk

›Northeast US from Virginia to Maine

›Upper Midwest Wisconsin and Minnesota

›Mid-Atlantic states

›Northern California

›Tick attachment duration

›Attachment >= 36 to 48 hours required for significant transmission risk

›Nymphal tick small size means attachment often unnoticed

›Seasonal risk

›Peak May through August coinciding with nymphal tick activity

›Nymphal stage most responsible for human transmission

Constitutional and systemic symptoms

›Systemic features

›Fever

›Low-grade in early localized disease

03Physical Exam/exam71

Vitals and general

›Vital sign assessment

›Temperature

›Low-grade fever in early localized disease

›High fever raises coinfection with Anaplasma or Babesia

›Heart rate

›Bradycardia with Lyme carditis and AV block

›Heart rate < 50 bpm triggers pacing assessment

›Blood pressure

›Hypotension with hemodynamically significant AV block

›SBP < 90 mmHg requires urgent intervention

›Oxygen saturation

›Baseline assessment

›Decreased in heart failure from carditis

Skin exam

›Erythema migrans findings

›Lesion morphology

›Expanding erythematous patch >= 5 cm

›May be homogeneous or target shaped with central clearing

›Lesion distribution

›Single lesion at bite site in early localized disease

›Multiple lesions at distant sites in early disseminated disease

›Important negatives

›No vesicles unlike HSV infection

›No purulence unlike cellulitis

›No scaling unlike tinea corporis

Neurologic exam

›Cranial nerve examination

04Differential Diagnosis/ddx69

Life-threatening mimics

›Urgent differentials

›Complete heart block from other causes

›ICD-10 I44.2

›Idiopathic fibrosis Lenegre disease

›Cardiac sarcoidosis

›Bacterial meningitis

›ICD-10 G00.9

›Purulent CSF with neutrophilic pleocytosis

›Rapid deterioration without treatment

›Septic arthritis

›ICD-10 M00.9

›High fever and erythematous joint

›Positive synovial fluid culture

Rash mimics

›Erythema migrans differential

›Southern tick-associated rash illness STARI

›Clinically indistinguishable from EM

›Caused by Amblyomma americanum tick bite

›Geographic overlap in southeastern US

›Cellulitis

›Tender warm with clear margins

›No central clearing

›Often with lymphangitis

›Tinea corporis

›Scaling erythematous border

›KOH preparation positive

›Slowly expanding

05Laboratory Tests/lt73

Serologic testing

›Two-tiered serologic testing

›Step 1 ELISA screening

›IgG and IgM antibodies against B burgdorferi

›Sensitivity < 40% in first 1 to 2 weeks of EM

›Sensitivity rises to > 90% in disseminated disease

›Step 2 Western blot confirmation

›Performed only if ELISA positive or equivocal

›IgM Western blot positive if >= 2 of 5 bands present

›IgG Western blot positive if >= 5 of 10 bands present

›Critical interpretation rules

›Western blot not valid if ELISA negative

›After 4 weeks of symptoms use IgG Western blot only

›False positives from EBV syphilis and autoimmune disease

›Repeat serology indications

›If initially negative with high clinical suspicion

›Repeat in 2 to 4 weeks

›Seroconversion often occurs by 4 to 6 weeks

›Do not retest after treatment

›Antibodies remain elevated for months to years

›Rising titers do not indicate active infection

Coinfection workup

›Coinfection labs when high fever persists on antibiotics

›Complete blood count with differential

›Leukopenia and thrombocytopenia suggest anaplasmosis

›Hemolytic anemia features suggest babesiosis

›Peripheral blood smear

›Intraerythrocytic ring forms for Babesia microti

06Diagnostic Tests/dt90

Scoring Systems

›Suspicious Index in Lyme Carditis SILC score

›Scoring components

›Erythema migrans present +4 points

›Known tick bite +3 points

›Constitutional symptoms +2 points

›Outdoor activity in endemic area +1 point

›Male sex +1 point

›Age < 50 years +1 point

›Risk stratification

›Low risk 0 to 2 points

›Intermediate risk 3 to 6 points

›High risk 7 to 12 points

›Clinical use

›High risk warrants empiric treatment for Lyme carditis

›Validated in emergency settings for AV block evaluation

›Rule of 7s pediatric Lyme meningitis

›Components

›Headache duration >= 7 days

›CSF mononuclear cells >= 70%

›Cranial nerve palsy present

›Interpretation

›Presence of all three supports Lyme meningitis over aseptic meningitis

›Helps guide empiric treatment in pediatric patients

ECG

›ECG findings in Lyme carditis

›AV block spectrum

›First-degree AV block PR interval > 200 ms

›Second-degree Mobitz type I Wenckebach most common

›Third-degree complete AV block in up to two-thirds of Lyme carditis cases

›PR interval monitoring threshold

›PR >= 300 ms warrants hospital admission and continuous monitoring

›Fluctuation from first-degree to complete block within minutes is characteristic

›Less common findings

›Bundle branch block

›Atrial and ventricular arrhythmias

›ST-T wave changes from myocarditis

›ACEP recommendation

›ECG in all patients with suspected disseminated Lyme disease

›Palpitations syncope or exercise intolerance triggers ECG

MRI

›MRI brain and spine in neuroborreliosis

›Indications

›Suspected Lyme encephalitis or encephalopathy

›Radiculopathy evaluation

›Exclude structural mimics of Lyme neuroborreliosis

›Findings in neuroborreliosis

›Leptomeningeal enhancement on gadolinium sequences

›Cranial nerve enhancement particularly CN VII

›White matter signal changes in encephalopathy

›MRI cardiac indications

›Myocarditis characterization in Lyme carditis

›Late gadolinium enhancement pattern

›Pericardial inflammation assessment

›Limitations

›Normal MRI does not exclude Lyme neuroborreliosis

›Availability and time constraints in acute setting

CT

›CT head in Lyme meningitis workup

›Indications

›GCS < 13 or focal neurologic deficit before LP

›Papilledema or signs of raised ICP

›Immunocompromised patient

›Expected findings

›Usually normal in Lyme meningitis

›Excludes mass lesion or hydrocephalus before LP

›CT chest in suspected Lyme pericarditis

›Pericardial effusion assessment

›Mediastinal adenopathy evaluation

›Contrast considerations

›Renal function assessment before contrast

›Allergy history review

Ultrasound

›Cardiac ultrasound echocardiography

›Indications in Lyme carditis

›Ventricular function assessment

›Pericardial effusion detection

›Valvular abnormality assessment

›Findings

›Left ventricular systolic dysfunction in myocarditis

›Pericardial effusion in pericarditis variant

›Usually normal valve structure

›POCUS at bedside

›Rapid ventricular function estimate in hemodynamically unstable patient

›IVC assessment for fluid responsiveness

›Musculoskeletal ultrasound

›Joint effusion detection

›Knee effusion quantification

›Baker cyst identification

›Guidance role

›Arthrocentesis guidance for knee effusion

›Aspiration accuracy improvement

›Differentiation from septic arthritis

›Imaging alone cannot differentiate Lyme from septic arthritis

›Synovial fluid analysis required

07Disposition/dispo36

Admission indications

›Mandatory admission criteria

›Lyme carditis with AV block

›PR >= 300 ms requires telemetry admission

›Any second or third-degree AV block

›Syncope or hemodynamic instability

›Neuroborreliosis requiring IV therapy

›Lyme meningitis

›Encephalopathy

›Severe radiculopathy with functional impairment

›Unable to tolerate oral medications

›Persistent vomiting

›Malabsorption concerns

›ICU indications

›Complete heart block with hemodynamic instability

›Requiring transcutaneous or transvenous pacing

›SBP < 90 mmHg despite atropine

›Encephalopathy with declining GCS

›Airway protection concern

›Continuous monitoring required

Discharge criteria

›Outpatient management criteria

›Early localized erythema migrans

›Hemodynamically stable with no cardiac symptoms

›No neurologic deficits

›Able to take oral antibiotics

›First-degree AV block only with PR < 300 ms

›Daily or twice daily ECG monitoring arranged

08Treatment/t82

Post-exposure prophylaxis

›Single dose prophylaxis after tick bite

›Doxycycline 200 mg PO single dose

›Within 72 hours of tick removal

›High-risk tick defined as Ixodes scapularis attached >= 36 hours

›In endemic area

›Efficacy

›Reduces risk of Lyme disease by approximately 87%

›IDSA Class I recommendation for eligible patients

›Contraindications to prophylaxis

›Pregnancy first trimester

›Child < 8 years old

›Allergy to tetracyclines

Early localized disease treatment

›Oral antibiotic regimens for erythema migrans

›Doxycycline 100 mg PO twice daily x 10 days

›Preferred agent for non-pregnant adults

›Also treats coinfection with Anaplasma

›Take with food to minimize GI side effects

›Amoxicillin 500 mg PO three times daily x 14 days

›First-line alternative for pregnant patients and children >= 8 years old

›Does not treat Anaplasma coinfection

›Cefuroxime axetil 500 mg PO twice daily x 14 days

›Alternative for doxycycline and amoxicillin intolerance

›Equal efficacy to amoxicillin

›Second-line azithromycin 500 mg PO daily x 7 days

›Lower efficacy than first-line agents

›Reserve for doxycycline and beta-lactam intolerance

›IDSA weak recommendation

Early disseminated disease treatment

›Facial palsy without meningitis

›Doxycycline 100 mg PO twice daily x 14 to 21 days

›Oral therapy sufficient if no meningitis on LP

›Lumbar puncture recommended to exclude Lyme meningitis

›Amoxicillin or cefuroxime as alternatives for 14 to 21 days

›Same dosing as early localized disease

›Duration extended for disseminated disease

›Lyme carditis treatment

›First-degree AV block PR < 300 ms mild carditis

›Doxycycline 100 mg PO twice daily x 14 to 21 days

›Close outpatient monitoring if PR < 300 ms

›High-degree AV block or PR >= 300 ms

›Ceftriaxone 2 g IV daily x 14 days

›Switch to oral doxycycline when PR normalizes

›Oral step-down to complete 21 day total course

›Cardiac monitoring until AV block resolves

›Temporary pacing if hemodynamically compromised

Neuroborreliosis treatment

›Lyme meningitis

›Ceftriaxone 2 g IV daily x 14 days

›Class I recommendation

›IV route required for CNS penetration

›Repeat LP not routinely required after treatment

›Alternative penicillin G 18 to 24 million units IV daily in divided doses x 14 days

›Reserve for ceftriaxone allergy

›Equivalent efficacy

›Encephalopathy and late neuroborreliosis

›Ceftriaxone 2 g IV daily x 14 to 28 days

›IDSA recommendation for CNS involvement

›Oral doxycycline may be alternative for some encephalopathy presentations

Lyme arthritis treatment

›Initial oral therapy for Lyme arthritis

›Doxycycline 100 mg PO twice daily x 28 days

›First-line for uncomplicated Lyme arthritis

›IDSA Class I recommendation

›Amoxicillin 500 mg PO three times daily x 28 days

›Alternative for doxycycline intolerance

›Equal efficacy

›Antibiotic-refractory Lyme arthritis

›Second oral course x 28 days before IV therapy

›Persistent synovitis after first oral course

›If persists after two oral courses consider IV ceftriaxone

›IV ceftriaxone 2 g IV daily x 28 days

›For refractory cases after two oral courses

›Rheumatology consultation recommended

›Anti-inflammatory therapy for refractory arthritis

›NSAIDs for symptomatic relief

›Hydroxychloroquine consideration in antibiotic-refractory cases

›Do not use prolonged antibiotics beyond evidence-based courses

Contraindicated and ineffective treatments

›Prolonged antibiotic courses

›Not indicated for post-treatment Lyme disease syndrome

›IDSA strong recommendation against

›No benefit shown in multiple randomized controlled trials

›Significant risks including C difficile and IV access complications

›Post-treatment Lyme disease syndrome management

›Symptom management and supportive care

›Exclude active infection before labeling syndrome

09Special Populations/sp59

Pregnancy

›Pregnancy-specific considerations

›Potential fetal risks from untreated Lyme

›Case reports of adverse fetal outcomes with untreated infection

›Active treatment strongly recommended

›No evidence of congenital Lyme syndrome with treated maternal infection

›Antibiotic selection in pregnancy

›Doxycycline contraindicated after first trimester

›Risk of fetal tooth discoloration and bone growth inhibition

›Avoid throughout pregnancy when alternatives exist

›Amoxicillin 500 mg PO three times daily x 14 days

›Preferred oral agent in pregnancy

›Safe in all trimesters

›Cefuroxime axetil 500 mg PO twice daily x 14 days

›Alternative oral agent in pregnancy

›Category B agent

›Ceftriaxone 2 g IV daily for disseminated disease

›Safe in pregnancy for meningitis carditis or severe disseminated disease

›Obstetric co-management

›Fetal monitoring in viable gestation with disseminated disease

›Maternal-fetal medicine consultation for complex cases

Geriatric

›Geriatric-specific considerations

›Atypical presentation in older adults

›EM rash may be less distinct or missed

›Constitutional symptoms may dominate

›Cognitive changes as presenting feature of late neuroborreliosis

›Comorbidity interactions

10Background/b81

Epidemiology

›Incidence and distribution

›Most common vector-borne infection in northern hemisphere

›Approximately 476,000 cases treated annually in United States

›True incidence estimated 10-fold higher than reported cases

›Underreporting and underdiagnosis significant

›Geographic distribution

›Northeast US accounts for majority of cases

›Upper Midwest Wisconsin and Minnesota second highest burden

›Expanding geographic range with climate change

›Demographic patterns

›Bimodal age distribution children 5 to 15 years and adults 45 to 55 years

›Slight male predominance in overall Lyme disease

›Lyme carditis predominantly affects males under 50 years

›Seasonal peak

›May through August coinciding with Ixodes nymphal activity

›Nymphal stage responsible for majority of human transmission

›Late season adult tick bites more common in November

Pathophysiology

›Causative organism

›Borrelia burgdorferi sensu stricto

›Gram-negative spirochete

›North American primary species

›European species

›B afzelii predominant in Europe

›B garinii associated with neurotropic disease in Europe

›Tick vector

›Ixodes scapularis deer tick in Northeast and Midwest US

›Ixodes pacificus western black-legged tick in California

›Transmission requires >= 36 to 48 hours attachment for significant risk

›Disease stages and mechanisms

›Early localized stage days to weeks

›Local skin invasion and replication

›Erythema migrans from inflammatory response

›EM appears 3 to 30 days after tick bite

›Early disseminated stage weeks to months

›Hematogenous spread to heart joints and nervous system

›Immune evasion via outer surface protein variation

›Multiple organ tropism

›Late disseminated stage months to years

›Persistent infection in joints

›Autoimmune-mediated joint inflammation in Lyme arthritis

›Antibiotic-refractory arthritis from immune dysregulation

›Organ-specific mechanisms

›Lyme carditis mechanism

›Spirochete invasion of cardiac tissue and conduction system

›AV node inflammation causing conduction delay

›Usually reversible with antibiotic treatment

›Lyme neuroborreliosis mechanism

›CNS invasion via hematogenous spread

›Inflammatory response in meninges and cranial nerves

›Intrathecal antibody production

Therapeutic Considerations

›Antibiotic selection principles

›Doxycycline advantages

›Treats B burgdorferi and Anaplasma coinfection

›Excellent oral bioavailability

›Cost-effective

›Beta-lactam advantages in pregnancy and young children

›Safety profile well established

›Amoxicillin and cefuroxime equivalent efficacy

›IV ceftriaxone for CNS and severe cardiac disease

›Superior CNS penetration

›Required for meningitis and severe neuroborreliosis

›Treatment duration evidence

›Shorter courses equivalent to longer for early localized disease

›10-day doxycycline equivalent to 20-day regimen for EM

›Multiple randomized trials support shorter duration

›Extended courses increase adverse effects without benefit

›C difficile infection risk

›Venous access complications with IV therapy

›IDSA strong recommendation against prolonged courses

›Post-treatment Lyme disease syndrome

›Defined as persistent symptoms > 6 months after adequate treatment

›Fatigue cognitive difficulties musculoskeletal pain

›Affects approximately 10 to 20% of treated patients

›Pathophysiology uncertain

›May reflect immune dysregulation

›Post-infectious mechanism

›Not active persistent infection

›Management approach

›Symptom-directed therapy

›Exclude reinfection or alternative diagnoses

›Prolonged antibiotics contraindicated

11Patient Discharge Instructions/pdi47

copy discharge instructions

›Lyme disease home care

›Take all antibiotics exactly as prescribed until finished

›Do not stop early even if feeling better

›Doxycycline take with food and full glass of water

›Remain upright for 30 minutes after doxycycline dose to prevent esophageal ulceration

›Sun protection with doxycycline

›Sunscreen and protective clothing while outdoors

›Risk of severe sunburn photosensitivity reaction

›Activity guidance

›Rest as tolerated during antibiotic course

›Resume gradual activity as symptoms improve

›Avoid strenuous activity if cardiac symptoms present until cleared by physician

›Warning signs to return to ER

›Cardiac symptoms

›Fainting or near-fainting episodes

›Palpitations or irregular heartbeat

›Shortness of breath with minimal activity

›Chest pain or pressure

›Neurologic symptoms

›Facial drooping on one or both sides

›Severe headache with neck stiffness

›Confusion or unusual behavior

›Weakness or numbness in arms or legs

›Severe joint swelling

›Hot swollen joint with high fever

›Inability to bear weight on joint

›Allergic reaction to antibiotics

12References/r20

Guidelines and key sources

›IDSA AAN ACR guidelines

›2020 IDSA AAN ACR Clinical Practice Guidelines for Prevention Diagnosis and Treatment of Lyme Disease

›Comprehensive evidence-based recommendations for all disease stages

›Strong recommendation against prolonged antibiotic therapy for post-treatment syndrome

›IDSA Level of Evidence framework used for antibiotic duration and selection

›Cardiac Lyme disease references

›Suspicious Index in Lyme Carditis SILC score validation studies

›Risk stratification for AV block in suspected Lyme carditis

›Emergency medicine application

›American Heart Association guidance on Lyme carditis and pacing indications

›Neuroborreliosis references

›Rule of 7s validation studies in pediatric Lyme meningitis

›Distinguishes Lyme from aseptic meningitis in endemic areas

›European Federation of Neurological Societies guidance on neuroborreliosis

›Coding standards

›ICD-10 A69.20 Lyme disease unspecified

›ICD-10 A69.21 Meningitis due to Lyme disease

›ICD-10 A69.22 Other neurologic disorders in Lyme disease

›ICD-10 A69.23 Arthritis due to Lyme disease

›ICD-10 I44.2 AV block complete when Lyme carditis presenting feature

Evidence & Review