| Affiliation |
(AGL) Chairman, Department of Ophthalmology, The Methodist Hospital, Houston, Texas; Professor of Ophthalmology, Weill Cornell Medicine, New York City, New York; (RS) Baylor College of Medicine, Houston, Texas |
| Transcript |
What I want to talk to you now is syphilis serology for neurophthalmology and you don't need to know everything about syphilis serology, but you need to knowhow to order the tests and how to interpret the tests. So, the two types of tests are treponemal tests and non-treponemal tests. The treponemal tests are identified by the letter T and so you've got choices FTAABS as a T, MHATP, micro hemagglutination for treponema pallidum, the treponema pallidum plasma agglutination test, and the syphilis treponema pallidum IgG. There are non-treponemal tests. These don't have a T.NoT. That's therapid plasma reagent(RPR)and the venereal disease research laboratory test (VDRL). We need to have both a treponemal test and a non-treponemal test, and the reason is the treponemal testis very specific and very sensitive. But once the treponemal test is positive it's positive for life. So that's usually just reported as a positive or negative or reactive or non-reactive. So, in this example FTA it's just positive and then it just stays positive. However, the non-treponemal tests they go up and if you're treated, right here, it'll have a four-fold reduction after treatment and usually it goes to zero. Some people remain serofast, at a low titer, and that means you need to know this original titer before you can assess the reality, uh, real significance of the titer if it's still positive. It's negative, you're fine. The problem with the RPR and the BDRL is sometimes it goes down for no reason and that is no treatment. So, we have a spontaneous reversion rate of the non-treponemal ant tests to negative even if you got no treatment. And so that makes the interpretation of these tests a lot more difficult. So, some are easy. If the FTA is positive and the RPR is positive well that's easy. You have syphilis. And the CDC says if you have this serology, and you have any eye finding that that's neurosyphilis and that means you have to have a lumbar puncture. And that means intravenous penicillin for two weeks because neurosyphilis is treated differently than primary or secondary symptoms. Likewise, if the FTA is negative and the RPR is negative that's also an easy one because that means they don't have it. The harder ones are when one is positive, and one is negative. Do the easy one first: the RPR is negative, and the FTA is positive. So, if this person right here can show that they had penicillin treatment(a piece of paper documenting it)that's good enough because the FTA is positive, and they were treated. If they cannot produce this piece of paper then it could still be this other choice, which is a false negative RPR. If the RPR is positive but the FTA is negative, that usually means that this is a false positive because the non-treponemal tests are not as good as the treponemal tests. In both of these circumstances, you could repeat the treponemal test. So, if we do a second treponemal test here, like MHTP or syphilis IgG, and the second test is negative, if two out of the three tests are negative, just go with the two out of the three and we'll just ignore the minority report. Same thing here. If you really want top rove that this is a false positive and this is a true negative, and we'll just do another treponemal test. And if two of the three are negative then that that's enough. You should also know that sometimes the RPR goes negative because the test is bad, and the test is optimized for a zone where the antibody and the antigen can agglutinate. So, it's an agglutination test where the antibody binds onto the antigen and if you have enough of these guys then you'll see a blob of black stuff and that is the agglutination. However, if we have a circumstance where we have too much antibody, there's just too much of this antibody going around, then they won't get to glom together because there's not enough antigen to go around. There's too many antibodies. And you can get the other version of it, which is too much of the antigen so it like sucks up everybody and they also don't get to agglutinate. So, either the too much antigen or the too much antibody can cause the test to be negative even though it's really positive. And that is called the prozone effect. Prozone. And one of the ways we can make that go away is we just keep tittering it. Keep diluting it diluting it more and then eventually you'll end in the zone. So even if it's negative at one to one and one to two or one to four all of a sudden one to eight is positive. So, we can kind of keep diluting it until we can get past this into the zone. So, you need to know a little bit about syphilis serology. We order it on any unexplained neurop finding, whether it's pupil or optic neuropathy or cranial neuropathy or nystagmus it can be anything because syphilis is the great mimicker. Can't really tell who has syphilis by looking at them. They could be old person, young person; you can't tell by gender. There are risk factors. The major risk factor in the United States is male to male sex transmission. However, it can happen in either gender. And regardless of what your sexual preference is, it doesn't matter. You can always get syphilis. And it can mimic anything so I'm going to order both the treponemal and anon-treponemal antibody in that setting. And if the tests serology are positive, if it's in the eye CDC says that's neurosyphilis. We're going to do the lumbar puncture and that means intravenous penicillin |
