Source Medecine news line 16 may 2018
Lyme : the great bazaar of diagnostic tests
Lyme disease or not ? It is a diagnosis that would confuse the Dr House
In the Face of a patient with severe fatigue, joint pain, cardiac injury and/or neurological, the famous doctor lame would multiply the examinations and blood tests.
But in the case of this infectious disease transmitted by the bite of a tick, it is unlikely that the answer comes from the laboratory. The Borrelia bacteria responsible for the infection, has mastered the art of camouflage and sleight of hand in order not to be detected by the immune system and go unnoticed. “The body then produces little antibody response. However, the tests used in the laboratory, baptized Elisa and Western Blot, are looking for these molecules in the blood, explains Sandrine Capizzi-Banas, senior lecturer in parasitology at the faculty of pharmacy of Nancy.
It is not known whether this failure of the immune system is caused by the bacterium, or if the people who develop Lyme are more fragile. “With this biological limit is in addition also the technical constraints. Even when anti-Borreliasont present in the blood, the results can be negative.
“The work conducted by british researchers from the Imperial College of London have shown that the sensitivity does not exceed 60 %, is professor Christian Perronne, infectious disease specialist at the hospital of Garches. In addition, the tests do not look for that the three bacteria responsible for Lyme, while it is known that a dozen agents are pathogens responsible for this disease. ” A limit, already highlighted by the High Council public health (HCSP) in 2014. Treatment antibiotiqueTraquer the DNA of the bacteria is another track of diagnosis of Lyme borreliosis. It is especially used in some labs German.
But then again it often leads to a cul-de-sac. “The amplification of DNA by PCR assay is effective to detect HIV, for example, because the virus is very present in the blood. But this is not the case with the bacterium Borrelia.
The results may be negative so that the patient is indeed suffering from Lyme,” says infectious diseases physician. But then why continue to practice these tests? And how can I be sure that a patient suffers from Lyme? It is necessary to rely on the clinic, meet the two experts. “Serological tests are not the solution. They do not allow to identify properly the sick.
Their only interest is to distinguish between Borrelia infection of multiple sclerosis, infectious diseases or reaction, auto-immune diseases, which can lead to symptoms similar to those of Lyme,” says Sandrine Capizzi-Banas, who recalls, in passing, that the use of these diagnostic tests is required of the sick by the social Security to repay their care.
Remains that, in practice, the diagnostic test, the most effective seems to be the antibiotic treatment.
“Patients with erythema migrans (sign absent in a case of two) must receive antibiotic treatment immediately. Similarly, patients with symptoms of lyme disease. And if their condition improves, it is that it was Lyme,” says the Pr Perronne.