Multiple Evanescent White Dot Syndrome
Multiple Evanescent White Dot Syndrome
Multiple Evanescent White Dot Syndrome (MEWDS) is one of the diagnoses within the family of White Dot/ White Spot Syndromes, first described by Jampol L. M and colleagues. Within this diagnostic group are MEWDS, Acute Posterior Multifocal Placoid Pigment Epitheliopathy (APMPEE), Mulifocal Choroiditis and Panuveitis (MCP), Punctate Inner Choroiditis (PIC), and Birdshot Choriorretinopathy. The White Dot Syndromes produce yellow-white retinal lesions classically located at the retinal pigment epithelium or outer retina and are found primarily in young adults. Symptoms of MEWDS include blurred vision, visual field loss, photopsias, and floaters. The various diagnoses are differentiated by history, appearance, laterality, and fluorescein angiogram findings.
Symptoms and Demographics
The typical patient with MEWDS is a healthy middle aged female age 15-50. There is a gender disparity as women are affected with MEWDS four times more often than men. Roughly 30% of patients have experienced an associated viral prodrome. Patients present with acute, painless, unilateral change in vision. They may notice photopsias, dyschromatopsia, or a temporal or paracentral scotoma. Majority of the cases have unilateral involvement, but bilateral MEWDS has been described and is usually asymmetric.
Though the onset is acute, the disease is typically self limiting and recurrences are rare. Visual prognosis is excellent.
On fundus exam, one sees flat, multifocal, grey-white lesions (100-200 microns), appearing to reach as deep as the RPE. Typically lesions are found outside the fovea in the posterior pole. A characteristic finding in MEWDS is an orange-yellow fovea with granularity. One might also note optic disc edema, mild vitritis (usually posterior vitreous cells), mild anterior chamber flare, a relative afferent pupillary defect and an enlarged blind spot. Sheathing of retinal veins and superficial retinal hemorrhages are rarely seen.
FA reveals early punctate hyperfluorescence in a wreath-like pattern and late staining, in areas corresponding to the white dots. Retinal vascular sheathing and optic nerve staining may be seen in some patients with MEWDS. This early hyperfluorescence and late staining is in contrast to acute posterior multifocal placoid pigment epitheliopathy (APMPPE) where early hypofluorescence is seen followed by late hyperfluorescence.
FAF is a quick and non-invasive method of establishing a diagnosis. Hyperautofluorescent dots correlate with the white dots seen on fundoscopy. Even in the absence of white dots on clinical examination, FAF can show characteristic hyperautofluorescent lesions. Recent reports suggest that FAF may be the most sensitive and practical ancillary test to detect MEWDS.
Optical coherence tomography
Discontinuities in inner segment-outer segment junction and mild attenuation of external limiting membrane have been reported in acute phase. Recurrent episodes may result in thinning of outer nuclear layer.
An enlarged blind spot is typically seen. Other features include a central or paracentral scotoma. Acute Idiopathic Blind Spot Enlargement Syndrome may represent a form of the same disease process.
Indocyanine green angiography
Hypocyanescent spots, typically outnumbering the clinical lesions are seen.
Changes are reversible. A reduced a-wave amplitude may be seen and early receptor potential may be prolonged.
A reversible decrease in Arden's ratio may be noted.
Visual evoked responses may show a reversible decrease in amplitude and prolongation of latency.
Pathogenesis and Treatment
An infectious etiology is thought to be involved in the pathogenesis of MEWDS since frequently there is a viral prodrome. However, the exact pathogenesis is unknown. Since MEWDS is a self-limited disease, with almost all patients regaining good visual acuity within 3-9 weeks, no treatment is recommended. Photopsias and scotomata gradually resolve and the lesions will disappear and may be replaced by mild pigment mottling or chorioretinal scarring. MEWDS typically is a self-limited disease, however, patients with MEWDS may have persistent blind spot enlargement. While it is uncommon, 10% of patients may also experience a recurrence. That being said, the prognosis is quite good for these patients.
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- Images used with permission from emedicine
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