New diagnostic methods may yield answers in uveitis

March 1, 2006

Chicago—Diagnostic techniques such as ocular fluid sampling, polymerase chain reaction (PCR), and genetic linkage analysis should be considered when a clinical examination fails to yield a definitive diagnosis of the etiology of primary inflammatory uveitis.

Chicago-Diagnostic techniques such as ocular fluid sampling, polymerase chain reaction (PCR), and genetic linkage analysis should be considered when a clinical examination fails to yield a definitive diagnosis of the etiology of primary inflammatory uveitis.

"Most of us think that idiopathic cases of uveitis are related to an autoimmune condition," said Bahram Bodaghi, MD, PhD, professor of ophthalmology, Pitié-Salpêtrière Hospital, University of Paris, France. "However, a large spectrum of infectious uveitis and masquerade syndromes requires diagnostic confirmation. Even though clinical examination remains the key point in most cases, in some challenging cases and conditions, lab testing, including serology and ocular fluid analysis, is very important to confirm diagnosis."

Speaking during the uveitis subspecialty day at the American Academy of Ophthalmology meeting, Dr. Bodaghi recommended that PCR, a technique for amplification of DNA in the laboratory, be performed when possible to identify pathogens.

Important considerations when performing PCR include selecting the oligonucleotide primer pair sequences, which are designed to identify complementary sequences of specific microbes, choosing appropriate positive and negative controls, and exercising caution in interpreting results, Dr. Bodaghi said. Potential pitfalls include high specificity with negative results and high sensitivity with false positive results.

As technology advances, clinicians are more frequently using real-time PCR, thanks to validation of the methodology in various studies, Dr. Bodaghi said. In real-time PCR, the amplification of the sequence of DNA is continuously monitored during cycling and can usually be detected early in the cycle rather than at the end-point of the reaction. This is usually achieved by monitoring changes in fluorescence within the PCR tube.

Real-time PCR offers advantages over conventional PCR such as speed, simplicity, reproducibility, quantitative capability, and low risk of contamination, Dr. Bodaghi said.

This technique can be particularly beneficial in diagnosing viral ocular diseases, including classic patterns such as herpetic keratitis, anterior uveitis, cytomegalovirus (CMV) retinitis, and acute retinal necrosis syndrome. It could also be a useful diagnostic tool with new entities that are arising, including chronic CMV uveitis associated with secondary glaucoma in immunocompetent patients, forms of Posner-Schlossman syndrome associated with CMV infection, rubella associated with Fuchs' heterochromic cyclitis, and herpes simplex virus linked to nonnecrotizing herpetic retinopathies.

Providing another instance in which PCR could be useful, Dr. Bodaghi noted that while it is often easy to diagnose classical forms of acute retinal necrosis syndrome or toxoplasmic retinal choroiditis clinically, in some cases there may be areas of extensive necrosis in the periphery mimicking herpetic acute retinal necrosis. These cases are usually associated with toxoplasmic infection.

"For parasitic conditions, evaluation of specific antibody production remains the gold standard, while for herpetic infections, PCR is very important," he said.

Other techniques

HLA typing is also an important tool in the diagnosis of noninfectious autoimmune conditions, particularly in patients presenting with a suspicion of HLA-B27 uveitis, birdshot retinochoroidopathy, Vogt-Koyanagi-Harada disease, or Behçet's disease.

Genetic linkage analysis is another step that can be extremely useful in the diagnostic procedure, Dr. Bodaghi said. This entails analysis of pedigrees rather than a case versus control approach. Using this technique, a group led by James T. Rosenbaum, MD, of the Casey Eye Institute, Portland, OR, genotyped 57 families multiplex for acute anterior uveitis at different markers and HLA alleles. They found that a specific locus on chromosome 9p predisposes individuals with ankylosing spondylitis to acute anterior uveitis (AAU). AAU affects about 40% of patients with ankylosing spondylitis.

"This appears to be the first study identifying a genetic region for AAU by genome-wide scan," Dr. Bodaghi said, adding that the site of this linkage between the two conditions was previously unknown.

Use of HLA-A29 typing is very important in birdshot retinochoroidopathy.

"You may reconsider your diagnosis if you have a patient with suspected birdshot retinochoroidopathy without the presence of HLA-A29, but what about subtyping?" Dr. Bodaghi said.