Early Onset Drusen - Part II
A book by Arnold Sorsby, the ophthalmologist who provided the original description of Sorsby macular dystrophy
Our second post on this topic will discuss a number of conditions that can mimic early onset drusen.
Benign yellow dot maculopathy
This is a newly reported condition in 2017, and it appears to be inherited in an autosomal dominant manner (Borman et al., 2017). Affected individuals have bilateral yellow dots at the level of retinal pigment epithelium (RPE), which can be discrete or confluent. These dots are hyperfluorescent on autofluorescence imaging, and on OCT, the dots correspond to minimal irregularity in the RPE layer.
Visual acuity is good in most patients with this condition, and ERG perimeters minimally affected. Given this is a newly recognized condition, little is known about its long term prognosis, but it is generally believed that this condition has a benign course.
Benign flecks retinopathy (OMIM # 228980)
This is a condition characterized by widespread bilateral flecks involving the posterior pole and extending to the arcade. This appears to carry a benign course with normal visual acuity and electrodiagnostic testing result. The findings have been reported in family cohorts in autosomal dominant or recessive inheritance (Dorairaj et al., 2007). An association with PLA2G5 have been found.
ABCA4 (Stargardt) maculopathy (OMIM # 248200)
ABCA4 maculopathy is the most common cause of inherited retinal dystrophy. Affected patients tend to have variable degree of vision loss, though in early stages, visual acuity can be normal. Patients often have yellow flecks in the posterior pole which can mimic drusen. These are hyperautofluorescent, and surrounding areas of mottled autofluorescence indicating outer retinal / RPE disease can be present. Atrophic areas can develop as the disease progress, and progressive vision loss is the norm. This disease is inherited in an autosomal recessive manner.
There are a number of other genes ( for example ELOVL4 and PRPH2) which variants can mimic the appearance of ABCA4 (Stargardt) maculopathy.
Pattern macula dystrophy
This is a group of heterogenous macula dystrophy, which some of them have a genetic bases (PRPH2 for example), and others can be associated with systemic diseases (McArdle disease, myotonic dystrophy, maternally inherited diabetes and deafness) or drug toxicity (pentosan polysulfate).
Patients with pattern macula dystrophy often have normal visual acuity, and this tends to carry a more benign course comparing to other inherited macula diseases. A reticular pattern of outer retinal changes is typical, and this is best seen on infrared or autofluorescence imaging.
North Carolina macula dystrophy (OMIM # 136550)
This is a autosomal dominant condition affecting the macula region. Patients with stage 1 disease can have drusen like lesions in both eyes, but in more advanced cases, macula colobomas are seen. This condition is non progressive.
Sorsby macula dystrophy (OMIM 136900)
This is a rare condition due to a variant in TIMP3, and it is inherited in an autosomal dominant manner. Patients with this condition can have early drusen like lesions, and they tend to develop aggressive macula neovascular membrane associated with fibrosis in their 40s. Frequent examination and imaging are essential to detect these neovascular membrane early along with ongoing self monitoring. Early aggressive treatment with anti-VEGF is required to preserve vision once these neovascular membrane is present.