Serology remains the main diagnostic tool for determining Lyme disease but the polymerase chain reaction (PCR) technique has attracted attention as an alternative method of diagnosing the condition in recent times. Such a technique is thought to have a high degree of sensitivity and specificity for detecting DNA of Borrelia bacteria with an ability to differentiate between species such as B. afzelii, B. garinii, and B. burgdorferi. Santino (et al, 2008) studied serum samples from 265 patients with positive, borderline, or negative ELISA and Western blot test results using PCR techniques and obtained positive results for PCR in all serum-positive samples and no incidence of false-positives. The researchers concluded that PCR testing may be a viable diagnostic technique for Lyme disease but more recent evidence suggests otherwise.
PCR Testing Does not Reveal Active Infection in all Lyme Patients
A 2011 study by Li, et al, looked at the presence of DNA, rRNA, and mRNA in skin samples of patients with erythema migrans, and samples of synovial fluid and tissue in patients with Lyme arthritis using PCR techniques. Whilst PCR testing appears to be accurate at detecting DNA this does not necessarily suggest active infection as DNA can be present long after the organism from which it came is no longer alive or viable. The assessment of mRNA however indicated spirochaetal viability and rRNA is suggestive of ribosomal activity allowing researchers to make judgements on the turnover, activity, and reproduction of bacteria such as Borrelia. PCR testing of synovial fluid found no evidence of mRNA even when patients had not yet been treated with antibiotics. The ratio of rRNA to DNA was also significantly lower in Lyme arthritis patients than in patients with erythema migrans and suggested minimal bacterial activity in the joints. Thus, PCR testing and detection of DNA in synovial fluid was determined to be unreliable in diagnosing active joint infection in Lyme disease
Lyme Disease Skin Lesions Tested with PCR
The same study did however find Borrelia burgdorferi DNA in most patients with erythema migrans lesions through PCR testing, along with mRNA in the majority of those patients. PCR testing appears, therefore, to be helpful in determining active infection in patients with manifest skin lesions. This is not necessarily useful in a clinical setting however as erythema migrans itself is considered sufficient for a diagnosis of Lyme disease in many cases. Where atypical skin lesions are seen it may be useful to establish the presence of active Borrelia bacteria in such cases using PCR testing but otherwise the expense and invasiveness of a skin biopsy will likely rule out such testing.
The sensitivity of PCR testing is thought to be around 50-70% in skin samples from cases of erythema migrans and acrodermatitis chronica atrophicans, whereas cerebrospinal fluid samples from neuroborreliosis patients demonstrated only 10-30% sensitivity for PCR testing or culture. PCR testing of synovial fluid shares a similar rate of sensitivity to skin samples (50-70%) but it is important to remember that these rates are for detection of DNA alone and do not, therefore, constitute any degree of confirmation of active disease. PCR testing is also vulnerable to contamination and inhibition, meaning that even high degrees of sensitivity and specificity under optimal conditions can be easily lost through poor processing and other factors. Nocton (et al, 1994) reported sensitivity of PCR testing of 96% from synovial fluid in American Lyme arthritis patients but these findings have not been reproduced in European studies. Figures of around 50-70% appear more common in studies of European patients with sensitivity increasing slightly where a larger sample size of synovial fluid was available. Similarly, sensitivity may be improved where PCR testing used more than one target sequence.
PCR Ineffective for Neurological Lyme Disease Patients
Patients with suspected neuroborreliosis are not considered good candidates for PCR testing as sensitivity appears to be quite low for Borrelia DNA in such cases. Lebech (et al, 2002) found evidence of B. burgdorferi DNA in just 17-21% of confirmed cases of neuroborreliosis in one study using cerebrospinal fluid samples. Those patients with early stage Lyme disease (<2 weeks) had the higher rates of PCR sensitivity however, compared with later stage neuroborreliosis, and the authors of the study suggest that PCR testing may be a helpful addition to diagnostic efforts in such an early stage. Serological testing for antibodies was still considered preferable to PCR testing in the majority of cases however. PCR testing of urine is not considered a suitable diagnostic tool, and serum samples are also unsuitable for this method of testing. Several companies continue to offer PCR tests amongst other types of tests for Lyme disease despite there being little, if any, evidence of sensitivity, specificity, or accuracy and with the CDC and EUCALB explicitly advising against such tests at the current time.
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Nocton JJ, DressIer F, Rutledge BJ, Tys PN, Persing DH, Steere AC. Detection of Borrelia burgdorferi DNA by polymerase chain reaction in synovial fluid from patients with Lyme arthritis. N Engl J Med 1994; 330: 229-234.
Lebech AM. Polymerase chain reaction in diagnosis of Borrelia burgdorferi infections and studies on taxonomic classification. APMIS Suppl. 2002;(105):1-40.
Santino I, Berlutti F, Pantanella F, Sessa R, del Piano M. Detection of Borrelia burgdorferi sensu lato DNA by PCR in serum of patients with clinical symptoms of Lyme borreliosis. FEMS Microbiol Lett. 2008 Jun;283(1):30-5. Epub 2008 Apr 1.