Diagnostic testing and disease monitoring in birdshot chorioretinopathy

Birdshot chorioretinopathy (BSCR) is a rare form of posterior uveitis in which hypopigmented choroidal lesions are scattered throughout the posterior pole. In order to avoid the poor natural history of BSCR, many practitioners would argue that it is critical to diagnose and carefully monitor the often subtle activity of this disease; BSCR can progress insidiously in a white and painless eye, and treatment algorithms based on visual acuity, vitreous inflammation, and retinal vascular leakage of fluorescein alone have been ineffective. This article reviews the various modalities that can be used to diagnose and monitor BSCR, including the clinical and ophthalmoscopic features, diagnostic criteria, electroretinography (ERG--full field, multifocal, and pattern), fluorescein angiography (FA), indocyanine green (ICG) angiography, optical coherence tomography (OCT), fundus autofluorescence (AF), visual fields, HLA A29 testing, and other laboratory testing. HLA-A29 testing can be useful in diagnostically borderline cases, but a positive test is not as useful as one might think in cases where the clinical suspicion for BSCR is low. Out of all the testing modalities, the ERG has been studied most extensively in its relationship to successful treatment. The key parameter is the 30 Hz flicker implicit time, which is abnormal in 70% of patients at baseline. A normal implicit time is correlated with the chance that a patient can be successfully tapered from systemic immunomodulatory therapy without recurrence. Alternatively, some practitioners use ICG angiography or visual field testing for adjunctive monitoring. OCT is used most commonly to follow macular edema. While there is no consensus on how to best monitor disease activity, our institution uses serial ERGs as an adjunct to the normal exam.