Ophthalmology – MEWDS (Multiple Evanescent White Dot Syndrome)

Basics

Description

Multiple Evanescent White Dot Syndrome (MEWDS) is an acute, idiopathic inflammatory white-dot syndrome involving primarily the outer retina and retinal pigment epithelium (RPE).

Typical features include:

• Sudden unilateral visual disturbance
• Multiple small white dots at the posterior pole
• Photopsias
• Enlarged blind spot or central/paracentral scotoma
• Characteristic foveal granularity
• Spontaneous recovery over several weeks
• Rare recurrence

It is usually self-limited.

Epidemiology

MEWDS typically affects:

• Young adults
• Most commonly patients in the 2nd to 5th decades
• Women in about 90% of cases

The disease is usually unilateral, although rare bilateral or asynchronous cases can occur.

Risk Factors

Approximately 50% of patients report a preceding viral-like illness.

A possible association with HLA-B51 has been described.

Pathophysiology

The exact mechanism is not fully understood.

Although historically considered primarily a choroidal inflammatory disorder, modern imaging suggests that the main abnormalities involve the:

• Photoreceptor outer segments
• Ellipsoid zone
• RPE–outer retinal complex

The disease is thought to represent an inflammatory or immune-mediated response.

Etiology

The cause is unknown.

Proposed mechanisms include:

• Viral trigger
• Postviral immune response
• Genetic susceptibility combined with an environmental trigger

Commonly Associated Conditions

MEWDS has clinical overlap with:

Acute Idiopathic Blind Spot Enlargement Syndrome (AIBSES/AIBES).

Some authors consider MEWDS and other white-dot syndromes to represent related disorders along a disease spectrum.

Diagnosis

History

Typical presentation is:

• Sudden decrease in central vision in one eye

Patients may also report:

• Photopsias
• Central or paracentral scotoma
• Enlarged blind spot
• Mild dyschromatopsia
• Recent viral illness

Rarely, the disorder may affect both eyes.

Physical Examination

Common findings include:

• Mild myopia
• Mild relative afferent pupillary defect in some patients
• Mild vitreous inflammation
• Optic disc edema
• Multiple small, poorly defined white lesions in the posterior pole
• Lesions located at the level of the outer retina/RPE
• Orange or granular appearance of the fovea

Classic Finding

Foveal granularity is one of the most characteristic clinical signs of MEWDS.

Fluorescein Angiography

Fluorescein angiography classically shows:

• Early punctate hyperfluorescence
• Late staining
• Lesions arranged in a wreath-like pattern

High-Yield Pearl

MEWDS → wreath-like hyperfluorescence on fluorescein angiography.

Optical Coherence Tomography

OCT commonly demonstrates transient disruption of:

• Ellipsoid zone
• Photoreceptor outer segments
• Interdigitation zone

These abnormalities generally improve as the patient recovers.

Indocyanine Green Angiography

ICG is usually not necessary to establish the diagnosis.

When performed, it typically shows:

• Multiple hypofluorescent spots

The number of lesions on ICG is often greater than the number visible clinically or on fluorescein angiography.

Electroretinography

ERG may show transient abnormalities.

Electrophysiologic changes generally improve during recovery.

Laboratory Testing

Routine laboratory testing is usually unnecessary in a typical case.

MEWDS is primarily diagnosed clinically with the assistance of multimodal retinal imaging.

Additional testing should be considered if the presentation is atypical.

Differential Diagnosis

Important differential diagnoses include:

• Acute idiopathic blind spot enlargement syndrome
• Acute posterior multifocal placoid pigment epitheliopathy
• Acute macular neuroretinopathy
• Multifocal choroiditis
• Birdshot chorioretinopathy
• Other white-dot syndromes

In older patients, particularly those over 50 with unusual or persistent findings, consider:

• Primary vitreoretinal lymphoma

Treatment

Observation

Observation is the usual treatment.

Most patients do not require medication because the condition is:

• Self-limited
• Mild to moderately vision-threatening
• Associated with spontaneous recovery

Symptoms usually improve within:

Several weeks to 1–2 months.

Referral

Referral to a retina or uveitis specialist should be considered if:

• Diagnosis is uncertain
• Disease is bilateral
• Findings are atypical
• Vision does not improve
• Symptoms recur
• Choroidal neovascularization is suspected

Follow-Up

Patients can usually be followed approximately:

• Monthly until symptoms and retinal findings resolve
• Thereafter as needed

Follow-up should assess:

• Visual acuity
• Visual symptoms
• Fundus appearance
• OCT abnormalities
• Optic disc changes

Prognosis

The prognosis is excellent.

Most patients recover to:

• 20/40 or better
• Frequently their previous baseline vision

Recovery usually occurs within several weeks.

Recurrence is rare.

Some patients may have subtle persistent symptoms despite good central visual acuity, particularly:

• Photopsias
• Enlarged blind spot

Complications

Complications are uncommon.

A rare complication is:

• Choroidal neovascularization

Key Clinical Pearls

• MEWDS typically affects young women.
• Usually presents with acute unilateral photopsias and mildly reduced vision.
• About 50% have a preceding viral-like illness.
• Multiple small white dots are found at the posterior pole.
• Foveal granularity is highly characteristic.
• Fluorescein angiography shows wreath-like punctate hyperfluorescence.
• OCT shows transient outer retinal/ellipsoid-zone disruption.
• ICG reveals more hypofluorescent lesions than are visible clinically.
• Enlarged blind spot is common.
• Treatment is usually observation only.
• Recovery typically occurs within 1–2 months.
• Recurrence and choroidal neovascularization are rare.