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Lyme disease

Lyme disease - is an infection caused by the spirochaete Borrelia burgdorferi and transmitted by the bite of the Ixodes tick (host - deer) and can affect the skin, joints, nervous system, and heart. This infection is endemic in some parts of the world (northern USA and central Europe) and the most common cause of chronic arthritis (more common than Juvenile Idiopathic Arthritis [JIA]). 

It is important to distinguish the arthritis from Lyme disease (most commonly a monoarthritis affecting the knee) from JIA, septic arthritis and mycobacterial infection (see Table below). A travel history is important. The patient may not know that they have been bitten and there may be no rash.  Treatment is with antibiotics and in most cases the prognosis is excellent.

The clinical presentation has several phases:

  • Early localized- Erythema chronicum migrans skin rash, is the most common in children, occurring several days and even several weeks after the tick bite. The rash often occurs with a flu-like illness and there can be large skin lesions. 
  • Early disseminated - weeks after infection with neurological features (facial nerve palsy, meningitis and rarely meningoencephalitis), heart conduction defects and arthralgia
  • Late disease - is mainly involving joints, most commonly a single knee with intermittent, relatively painless large effusions lasting days or even weeks. Small joints are not affected. 
  • Diagnosis is made by exclusion of other infection and by DNA analysis of the synovial fluid or by serology (albeit the serological tests have low sensitivity and specificity is variable).
  • More information about Lyme disease is available from the Centre for Disease Control and Prevention. 

Differentiating between Lyme disease, Septic Arthritis and Juvenile Idiopathic Arthritis (JIA) 

Lyme arthritis

Septic Arthritis


A history of tick bite or travel to endemic areas with potential exposure to ticks.


May have extra-articular features (rash, uveitis).

Mostly monoarthritis and affecting large joints.

Small joints not affected.

Monoarthritis, any joint.

Pattern of joint involvement is variable. Any joints may be affected, any number.

Joint symptoms tend to be intermittent and joint can be swollen but relatively pain free.

May have rash (characteristic erythema migrans

May have neurological features (facial palsy, meningitis)

Joint pain severe and joint or limb held immobile. Often non-weight bearing. Patient systemically unwell with fever and malaise. 

Joint symptoms often variable with diurnal variation and by definition, last > 6 weeks.

May have normal acute phase reactants (ESR and CRP) and white cell count. 

Raised white cell count and acute phase reactants. 

May be febrile.

May have normal acute phase reactants (ESR and CRP) and white cell count

High synovial fluid white cell count. May be evidence of bacterial DNA in synovial fluid. 

Very high synovial fluid white blood cell count. Organisms cultured.

Moderately raised synovial fluid white cell count but sterile.