Lyme Disease

Lyme disease is a tick borne infection caused by spirochaetes of the Borrelia burgdorferi sensu lato complex. It is transmitted through the bite of infected Ixodes ticks. It produces a characteristic multisystem illness.

Untreated, the illness typically progresses through recognisable stages: early localised, early disseminated and late. Clinical manifestations and treatment vary according to the stage and organ system involved.

Pathophysiology and transmission

Transmission generally requires tick attachment for at least 24 to 36 hours, so prompt tick removal reduces infection risk.

If early localised infection is not treated, the spirochaete disseminates from the initial cutaneous site of inoculation via the bloodstream and lymphatics. This occurs over days to months. It affects skin, joints, the nervous system and, less commonly in most geographical regions, the heart.

Early localised disease presents with erythema migrans. This is an expanding, typically painless and non pruritic erythematous rash at the site of the tick bite, developing over three to thirty days. It classically, though not universally, shows central clearing giving a target like appearance.

Mild constitutional symptoms often accompany it (fatigue, headache, low grade fever, myalgia).

Early disseminated disease develops weeks to a few months after the initial infection if untreated. It can produce:

• Multiple secondary erythema migrans lesions.
• Facial nerve palsy, which may be bilateral (a relatively distinctive feature).
• Other cranial neuropathies.
• Lymphocytic meningitis.
• Radiculopathy.
• Cardiac involvement with atrioventricular conduction block, in some geographical regions more than others.

Late disease develops months to years after untreated infection. It is dominated by Lyme arthritis, typically intermittent or persistent mono or oligoarthritis affecting large joints, particularly the knee. Less commonly, there is a chronic encephalopathy or peripheral neuropathy.

Post treatment Lyme disease syndrome comprises persistent fatigue, musculoskeletal pain and cognitive complaints following appropriately treated infection. It is a recognised though incompletely understood entity, distinct from ongoing active infection. It does not respond to further or prolonged antibiotic treatment.

Erythema migrans in the appropriate clinical and epidemiological context (known or likely tick exposure in an endemic area) is diagnosed clinically. Serological confirmation is not needed, as antibody responses are frequently not yet detectable at this early stage. Do not delay treatment while awaiting serological results in a patient with a classical rash.

Serological testing is the standard diagnostic approach for disseminated or late disease, where antibody responses have generally had time to develop. It uses a two tier approach: an initial sensitive enzyme immunoassay, followed by a confirmatory immunoblot for positive or equivocal results.

Antibodies can persist for years after successfully treated infection. A positive result does not necessarily indicate active disease requiring treatment in the absence of a compatible clinical picture.

Cerebrospinal fluid analysis supports diagnosis of neurological involvement (Lyme neuroborreliosis). It includes specific antibody index testing, comparing intrathecal to serum antibody production.

Synovial fluid analysis shows non specific inflammatory changes. In suspected Lyme arthritis where the diagnosis remains uncertain, it can be tested for Borrelia polymerase chain reaction.

Electrocardiography is indicated where cardiac involvement is suspected, given the recognised risk of atrioventricular block. This can occasionally be high grade and require temporary pacing.

Early localised disease (erythema migrans without evidence of disseminated involvement) is treated with doxycycline 100 mg twice daily for 10 to 14 days as first line treatment in patients without contraindication.

Alternatives are amoxicillin 500 mg three times daily for 14 days or cefuroxime axetil 500 mg twice daily for 14 days. These are used particularly in pregnancy or in young children, where doxycycline has traditionally been avoided.

Current evidence suggests short courses are likely safe even in young children. Doxycycline is increasingly used more broadly, given its additional efficacy against other tick borne co-infections that may be acquired simultaneously.

Early disseminated disease with isolated facial nerve palsy and no other neurological involvement is treated with the same oral regimens as early localised disease, typically doxycycline 100 mg twice daily for 14 to 21 days. Oral treatment achieves adequate outcomes for isolated cranial neuropathy without other central nervous system involvement.

Lyme meningitis, radiculopathy or other central nervous system involvement beyond isolated facial palsy is treated with intravenous ceftriaxone 2 g once daily for 14 to 28 days, given the need for reliable central nervous system penetration. Some guidelines and clinical contexts consider oral doxycycline an effective alternative, particularly where intravenous access or prolonged hospital based treatment is impractical.

Lyme carditis with mild atrioventricular block (first degree, or asymptomatic second degree) can be managed with oral antibiotics as for early disseminated disease.

More significant conduction disease (symptomatic, high grade second degree, or third degree block) warrants:

• Admission for cardiac monitoring.
• Intravenous ceftriaxone 2 g once daily.
• Consideration of temporary pacing.

Permanent pacing is generally not required, given the typically reversible nature of Lyme related conduction disease once treated.

Lyme arthritis is treated with oral doxycycline 100 mg twice daily or amoxicillin 500 mg three times daily for 28 days. Consider a further course. For persistent or recurrent arthritis despite appropriate oral treatment, consider intravenous ceftriaxone 2 g once daily for 14 to 28 days.

Use nonsteroidal anti inflammatory drugs adjunctively for symptomatic joint pain. Some patients experience persistent post infectious synovitis despite adequate antimicrobial treatment and adequate spirochaete clearance.

Prophylactic treatment may be given as a single dose of doxycycline 200 mg after a recognised high risk tick bite. High risk means an identified Ixodes tick attached for at least 36 hours, in a highly endemic area, with treatment able to be started within 72 hours of tick removal.

Routine prophylaxis for all tick bites is not recommended. For lower risk exposures, the standard approach is watchful waiting, with prompt treatment if erythema migrans or other symptoms develop.

Prevention remains the most effective overall strategy, given the relationship between duration of tick attachment and transmission risk. It relies on protective clothing, tick repellent, and prompt, careful removal of attached ticks. Use fine tipped tweezers applied close to the skin with steady upward traction, avoiding twisting or crushing the tick body.