Birdshot Chorioretinopathy

Birdshot chorioretinopathy is a posterior uveitis characterized by multiple cream-colored, hypopigmented choroidal lesions in the fundus and a strong association with HLA-A29 and clinically presenting with blurred vision, floaters, photopsia, scotoma and nyctalopia.

Epidemiology

The disease is more common in North European descents with a female preponderance. It accounts for 6%-8% of cases of posterior uveitis. Prevalence in North Carolina is estimated to be 1/700,000.

Clinical description

The age of onset is usually the fifth or sixth decade of life. Patients often present with gradual deterioration of vision, floaters, photopsia, scotoma, nyctalopia, metamorphopsia and poor color and contrast sensitivity. Decreased visual acuity in early disease is attributed to macular edema. Persistent inflammation and optic disc edema can lead to optic atrophy and subsequent permanent visual loss. In majority of the patients, the disease is chronic and progressive while 20% of patients develop a limited disease with spontaneous remission. A systemic involvement including essential hypertension, cerebrovascular accidents, hearing loss, vitiligo (see this term) and psoriasis is rarely observed.

Etiology

Etiology is unknown but an organ -specific T-cell - driven autoimmune process is implicated, with both choroid and retina being independent targets and sites of inflammation. The Th17 system has also been implicated but this remains unconfirmed. A strong association with HLA-A29 is noted.

Diagnostic methods

The diagnosis is based on clinical findings, supportive flourescein angiography and HLA testing (<50% positive predictive value, as 8% of general population are HLA-A29+), The visual fields may show blind spot enlargement, central/ paracentral scotomas or constriction of the peripheral vision. Fundoscopy reveals characteristic multifocal, hypopigmented, ovoid, cream-colored lesions (50-1500 µm) at the level of the choroid and retinal pigment epithelium in the postequatorial fundus displaying a nasal and radial distribution. Angiography (Indocyanine green (ICG), flourescin) reveals multiple hypofluorescent spots (birdshot lesions), vascular leakage, macular edema, disc edema optic atrophy and neovascularization (in later stages).

Differential diagnosis

The differential diagnoses are those diseases that produce white dots in choroid and retina; they include white dot syndromes, vogt-Koyanagi-Harada disease, infectious etiologies (Lyme disease, tuberculosis, toxoplasmosis) and primary intraocular lymphoma (masquerade syndromes) (see these terms).

Genetic counseling

More than 95 percent of patients with birdshot chorioretinopathy are HLA-A29 positive. However, the disease is not considered heritable.

Management and treatment

Electroretinography, flourescin angiography and perimetry are important in the follow-up of patients with Birdshot retinopathy. While periocular, ocular, intravitreal and systemic corticosteroids may be effective in the short-term management of vitritis and macular edema, they are of inconsistent efficacy in the long run. Early introduction of corticosteroid-sparing immune modulatory treatment (cyclosporine, methotrexate, mycophenolate mofetil, azathioprine, tacrolimus, human immunoglobulin G) is advocated, as extended treatment is anticipated in most patients. For refractory cases, dacluzimab and infliximab has been helpful.

Prognosis

Preservation of central vision until late in the disease and induction of long-term remission are possible with treatment, however the long-term visual prognosis of this disorder remains guarded.