By Michael E. Zegans, MD
This retrospective study found that anti-tubercular treatment (ATT) for longer than nine months reduced the likelihood of inflammation recurrence by 11-fold in patients with latent tuberculosis (TB)-associated uveitis.
One can speculate that this apparent efficacy of ATT on the course of uveitis is due to killing Mycobacterium tuberculosis either in the eye or elsewhere in the body. However, it is also possible that these medications reduce uveitis due to off-target effects on other micro-organisms or the patient's immune system.
The authors reviewed the charts of all consecutive uveitis patients seen at a single, tertiary institution over nine years with uveitis consistent with TB, positive tuberculin skin test with other causes ruled out, and a minimum follow-up of six months after completion of treatment. Mean age was 45.3 years and most were female (n = 118, 57.6 percent) and Chinese (n = 104, 50.7 percent).
Of 182 eligible patients, 46 received ATT of ≥ six month's duration; 18 patients defaulted and received < six months of treatment. Patients who completed > nine months of ATT were less likely to experience recurrence compared with those not treated with ATT, while adjusting for potential confounders, such as patient demographics, anatomical location of uveitis and corticosteroid therapy. Patients treated with ATT for < six months or six to nine months did have a reduction in recurrence, but it was not statistically significant.
A sub-analysis found that patients who received ATT for > nine months had a better visual outcome at one year compared with those who did not receive any ATT, and that being female was an independent risk factor for recurrence of inflammation.
The authors stress that their data indicates that nine months, rather than six months, of ATT treatment is beneficial. In contrast, a smaller study in the April 2011 issue of Eye reported benefits with a six-month protocol. Thus, the ideal ATT protocol, both in terms of which ATT medications to use and the duration of treatment, is unclear. However, the authors conclude that patients with uveitis associated with latent TB and no other known etiology to account for their uveitis should be treated with ATT of at least nine months' duration.
There are a variety of reasons to consider treatment with ATT in a patient with evidence of TB infection and otherwise idiopathic uveitis. Even in uveitis unrelated to latent TB infection, many uveitis patients will require systemic immune-suppression during the course of therapy. Immunosuppression can promote reactivation of TB, thus endangering the patient. Therefore, treatment of latent TB has the added benefit of increasing the safety of the use of systemic immunosuppressive agents during the course of uveitis treatment, even if it does not alter the course of uveitis.
Clinicians must weigh the potential benefits of ATT with the risks of drug toxicity. Co-management with an internist or specialist would be beneficial to most ophthalmologists.
A significant limitation of this study is that it is retrospective. A prospective study would be of great value in better defining the benefits and risks of TB treatment in this clinical setting.