Pathophysiology
Lyme disease is a zoonotic infection caused by the Borellia species. These are spirochaetes with Outer surface proteins (Osps) which are designated by letters A-F. It is transmitted by the Ixodes scapularis tick, commonly known as the deer tick or black-legged tick. These ticks become infected through feeding on an infected animal.
- Borellia burgdorferi - more common in USA.
- Borellia afzelii - more common in Europe and Asia.
- Borellia garinii - more common in Europe and Asia.
After being bitten by the Ixodes tick, a period of more than 48 hours is usually needed to establish an infection. Borellia then moves throughout the ECM and binds to proteogylcans and other components that allow the infection and rash to expand (hence the erythema migrans). The infection is able to disseminate from skin → organs quickly.
The disease may then cause more severe chronic symptoms and can also lead to autoimmune issues affecting joints (Lyme arthritis).
🏘 Epidemiology
The incidence has been rising in recent years. It is most common in Northern USA and North-eastern Europe. It is the most common vector-borne infection in the USA.
It’s peace incidences have been identified in 2 age groups: 10-19 and 50-59 years old.
⚠️ Risk factors
- Infected tick bites - especially in skin folds as these areas are harder to identify, thus allowing for the time for infection to be transmitted.
- Outdoor activities
- Farming
😷 Presentation
We can classify the disease into 3 stages:
Stage 1
Lasts several weeks (usually within 30 days).
- Erythema migrans - a bulls-eye rash usually at the tick-bite site. It is usually painless and >5cm in diameter, but slowly increases in size. Remember, central clearing is classic but not always present, however.
- Flu-like symptoms - headache, lethargy, fever, arthralgia.
- Regional lymphadenopathy
- Borellia lymphocytoma - a blue patch on the earlobe, nipple or scrotum (common in children)
Stage 2
Early disseminated disease. May last days - months.
- Continued flu-like symptoms
- Neuroborreliosis
- Facial nerve palsy unilaterally (bilateral is less common but still possible), LMN type.
- Radicular pain
- Aseptic meningitis
- Encephalitis
- Cardiovascular
- Myopericarditis
- Heart block
- Arrhythmias
Stage 3
- Arthritis - usually of large joints (such as the knee). However, it is not destructive.
- Neurological disorders
- Acrodermatitis chronica atrophicans - blue-red discolouration on the extensor surfaces of the limbs.
🔍 Investigations
⭐️ NICE recommends clinical diagnosis if erythema migrans is present.
If negative → repeat ELISA at 4-6 weeks after initial test. If symptomatic for 12 weeks, then Lyme-specific immunoblot test should be performed.
🏆 If positive → Lyme-specific immunoblot test should be done.
🧰 Management
NICE does nto recommend routine antibiotic treatment if patients have suffered a tick bite. However, they are a common presentation to GP practices. The best way to remove them is with fine-tipped tweezers, grasping the tick as close to the skin as possible and pulling upwards firmly.
Prophylactic antibiotics may be given if all of the following criteria are met:
- High-risk tick bite with at least 36 hours of attachment in an endemic area for Lyme disease.
- Tick removal is <72 hour prior
- Doxycycline is not contraindicated. It is contraindicated in:
- Children <12 years old
- Pregnancy and lactation
- Doxycycline - 4.4mg/kg/day in children or 200mg OD in adults.
- Doxycycline - if early disease. If erythema migrans is present, doxycycline should be started without the need for further tests.
- 100mg orally BD in adults.
- 2.2mg/kg orally BD in children.
- Amoxicillin - if doxy is contraindicated .
- Ceftriaxone - if there is disseminated disease with risk of severe cardiac complications.
A Jarisch-Herxheimer reaction may be seen sometimes after starting antibiotics. This presents as a fever, rash and tachycardia after the first dose of antibiotics.
It occurs in patients with spirochaete infections such as Lyme disease and syphilis for example, after initiating antibiotics.