Educational draft · awaiting clinical reviewUse Rapid for revision, not patient-care decisions. Check current national and local guidance and the BNF or BNFC before acting.
2 min synopsisUK scopeSources checked 27 Aug 2026Clinical review pending
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Unstable Lyme carditis or severe neurological disease
Syncope, chest pain, breathlessness, marked PR prolongation, high-grade atrioventricular block, ventricular dysfunction, meningitis, encephalitis or rapidly progressive neurological deficit after possible tick exposure requires urgent hospital assessment.
Action: Use ABCDE, obtain ECG and continuous monitoring, investigate competing emergencies, involve cardiology or neurology with infection specialists, and start manifestation-appropriate intravenous ceftriaxone when indicated without waiting for delayed serology.
Synopsis
Recognise erythema migrans and disseminated Lyme borreliosis, use clinical diagnosis and two-tier serology at the right time, and select manifestation-specific treatment and escalation.
Lyme borreliosis is caused by Borrelia burgdorferi sensu lato transmitted by infected Ixodes ticks; risk rises with attachment duration but a recalled bite is not required.
Erythema migrans is an expanding erythematous lesion, usually appearing one to four weeks after a bite; it is not usually hot, painful or itchy and may lack textbook central clearing.
Diagnose erythema migrans clinically and treat without laboratory testing because early serology can be negative.
Key red flags
Syncope, presyncope, chest pain, dyspnoea or palpitations with PR prolongation or atrioventricular block may be Lyme carditis and can deteriorate rapidly.
Neuroborreliosis
Facial palsy, painful radiculoneuritis, sensory symptoms or lymphocytic meningitis can appear weeks after infection and require objective localisation.
Investigation priorities
01
Clinical diagnosis of erythema migransFirst step
Recognise the manifestation that does not require laboratory confirmation.
02
First-line Lyme antibody ELISAFirst line
Screen a symptomatic person without erythema migrans when Lyme disease is clinically plausible.
Management branches
ERYTHEMA MIGRANSDiagnose and treat clinically
A typical expanding lesion follows plausible tick exposure, with or without constitutional symptoms.
Document lesion size, appearance, onset and exposure; distinguish it from a small immediate hypersensitivity reaction that appears and resolves quickly after a bite.
Do not request serology routinely because antibodies may be absent and the result does not alter treatment of a typical lesion.
Key medicines
DoxycyclineGive 100 mg orally twice daily or 200 mg once daily for 21 days for erythema migrans, non-focal symptoms, cranial or peripheral neurological disease and stable carditis; use 28 days for arthritis or acrodermatitis.
AmoxicillinGive 1 g orally three times daily for 21 days for erythema migrans or non-focal disease, and for 28 days for arthritis or acrodermatitis when selected.
National guidance is shown before implementation-dependent detail. Typical adult dose examples remain subject to patient factors, contraindications and the live BNF or specialist protocol. Source check completed 27 Aug 2026; clinical approval remains outstanding.