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EW INTERNATIONAL 100 by Matt Young and Gloria D. Gamat EyeWorld Contributing Writers When patients present with uveitis, either as a bilateral multifocal choroiditis, or bilateral granulomatous iridocyclitis, the clinician should think of ocular TB—especially if the patient is from a population with a high incidence of primary tuberculosis. "The definitive diagnosis of TB is based on the proper identification of the organism, which is not a very easy task," Dr. Pavesio said. "One thing to keep in mind whenever we look at tuberculosis is that we have an element that is probably related to the invasion of the tissue by the microorganism, but also we cannot forget the possibility that a lot of what we see is the immunoreaction that is triggered by the organism." According to Dr. Pavesio, even with the knowledge of the different phenotypes more likely connected with TB, the diagnosis of TB-related uveitis remains a challenge. "Never forget TB as a potential cause of the uveitis you have in front of you, and interpret results of tests such as interferon gamma release essays (IGRA) with caution, always keeping in mind the relevance of the clinical features that must be compatible with the diagnosis of TB," Dr. Pavesio said. "Pursue further examinations, and try [diagnostic tools] that will give you more certainty that the con- dition is TB-related," Dr. Pavesio concluded. "Proceed with full treatment, always keeping in mind accounted for 21.1% of those with TB, representing an increase from 16% in 1992. In ocular TB, the biggest setback to diagnosis is the lack of definitive diagnostic criteria. Clinicians have to rely on clinical experience and the diagnosis is mainly presumptive. "The reason for difficulty in diagnosis is because there is a huge polymorphism of lesions that are presented to us," Dr. Pavesio ex- plained. "There is no one lesion we can see to diagnose ocular TB. We have now developed a better under- standing of the phenotypes more likely to be connected to tuberculo- sis. But phenotypes differ geograph- ically and we have to be aware of these geographic differences." Presumed diagnosis: key to management? Because of its similarity to other causes of uveitis, the invasiveness of obtaining tissue samples, the limited volume of intraocular fluid sample, and the limitations of available diagnostic tests, ocular TB is difficult to diagnose. Thus, clinical suspicion becomes the imperative first step toward the correct diagnosis. Clini- cians use corroborative evidence, for instance, not ruling out ocular TB when certain inflammato y diseases are present in the eye. The complica- tions will not subside, despite mul- tiple visits to the doctor, if the root cause is TB. When untreated, ocular TB can lead to possible vision loss. Be on the lookout for a different kind of uveitis T uberculosis (TB) generally affects the lungs, but it can also affect extrapulmonary organs, including the eyes. "In terms of the manifesta- tion of [primary tuberculosis], once you are exposed to M. Tuberculosis, primary tuberculosis will happen in 5% of individuals," said Carlos Pavesio, MD, consultant ophthalmic surgeon, Moorfields Eye Hospital, U.K., who spoke at the National Healthcare Group (NHG) Eye Institute 7th International Oph- thalmology Congress in Singapore. "The [M. Tuberculosis] infection will remain dormant with a risk of reactivation in the majority of the people affected," he said. "There is a very small percentage of individuals who will eventually develop ocular tuberculosis as a consequence of this exposure." The World Health Organization (WHO) estimates that 8.7 million people are affected by tuberculo- sis (TB), and 5.8 million people were newly diagnosed in 2011. TB remains a big issue due to globaliza- tion, movement of people around the globe, and a growing concern about multidrug-resistant strains and also HIV individuals, who are more vulnerable to TB. No definite diagnostic criteri Although the number of people affected by ocular tuberculosis (also known as tuberculosis uveitis) is small compared to worldwide statistics on pulmonary tuberculosis, ocular TB poses a challenge to the eye doctor, mostly in terms of its diagnosis and therapeutic manage- ment. "It can affect any ocular tissue, but mainly without a distinct man- ifestation," Dr. Pavesio said. "This is very important: A lot of patients who come to see us present without a diagnosis of tuberculosis—they present with an ocular problem." In 2005, the Centers for Disease Control (CDC) reported that extrapulmonary TB with no evidence of pulmonary TB October 2014 Ocular tuberculosis: Challenges in diagnosis and management W hen we hear hoof beats outside the window, they are most likely coming from a horse, but not always. The art of differential diagnosis is one of the first things we learn in linical training. Considering all the possible diagnoses that could explain a clinical presentation remains an important step in patient care. Uveitis is a common finding that can be caused by uncommon condi- tions. This article reminds us that we need to consider all the possibilities. Sometimes the hoof beats we hear outside the window actually do come from a zebra. John A. Vukich, MD international editor International outlook "[Ocular TB] can affect any ocular tissue, but mainly without a distinct manifestation. This is very important: A lot of patients who come to see us present without a diagnosis of tuberculosis—they present with an ocular problem." –Carlos Pavesio, MD