Differential inflammatory involvement in retina and choroïd in birdshot chorioretinopathy

Birdshot chorioretinopathy is characterised by dual unrelated inflammatory involvement of the retina and the choroid. Indocyanine green angiography made it possible to assess and follow choroidal disease with the same precision as retinal involvement was followed so far. The aim of this study was to analyse the severity, progression and response to therapy of both retinal involvement using fluorescein angiography and choroidal involvement using indocyanine green angiography.

Patients with birdshot retinochoroidopathy followed at La Source Eye Centre in Lausanne, Switzerland from January 1995 to December 2002 were subdivided into three subgroups according to the duration of evolution of the disease: untreated patients with no more than one year duration of the disease (group 1, n = 6); treated patients with disease duration of 1 - 7 years duration (group 2, n = 5) and patients with disease lasting for more than 7 years (group 3, n = 4). Fluorescein and indocyanine green angiographic signs (angiographic scores given by a masked observer) were analysed in the 3 groups and compared to the "cream-coloured" fundus lesions.

Fifteen out of the 742 patients (2.0 %) seen at La Source Eye Centre during the time period considered presented BC and were included in the study. In the "early disease group" fluorescein and ICG angiography showed more severe choroidal than retinal involvement with respective scores of 3 +/- 0.79 (ICG) and 2 +/- 1.17 (FA) while there were few depigmented fundus lesions to be seen (score 1 +/- 0.27). The choroidal involvement responded well to systemic corticosteroids +/- immunosuppressive therapy (scores in groups 2 and 3 = 1.2 and 0.75), while retinal disease was stabilised at best (scores in groups 2 and 3 = 2.2. and 2.4) and depigmented fundus lesions increased (scores in groups 2 and 3 = 2.8 and 3).

The evolution and response to therapy of retinal and choroidal disease in birdshot chorioretinopathy have a different course with choroidal disease responding well to therapy while retinal disease is more resistant, possibly explaining the slow deterioration of functional parameters despite therapy. The increase of "cream-coloured" fundus lesions despite good choroidal response to therapy could be explained by depigmentation left behind after resolution of choroidal stromal granulomas, a hypothesis recently confirmed by an autopsy case of birdshot chorioretinopathy.