The White Dot Syndromes

Yoko Matsumoto, MD, PHD; Sebastian P. Haen, MD; Richard F. Spaide, MD

Disclosures

Compr Ophthalmol Update. 2007;8(4):179-200. 

In This Article

Diffuse Unilateral Subacute Neuroretinitis

In 1978, Gass published a series of articles about 29 patients who had the clinical syndrome that he named diffuse unilateral subacute neuroretinitis (DUSN).[5,94,138,139,140] Diffuse unilateral subacute neuroretinitis is a parasitic disease with protean manifestations caused by a nematode that may wander in the subretinal space for years.[138] Diffuse unilateral subacute neuroretinitis is most frequently diagnosed in the second and third life decade, but younger children and older people can also be affected. Men are more frequently affected than women.[141]

There is no racial preference. Endemic areas for DUSN are the Southeastern United States, the Caribbean area, and South America.[138,142,143] The nematode can survive in the human body for 4 years or longer and may be found in the subretinal space long after the development of severe retinal and optic disk changes.[138] The identification of these nematodes is still difficult. Several different types of nematodes have been proposed, but two seem to be the most likely.

The first one, presumably Ancylostoma caninum, is most frequently found in the Southeastern United States, the Caribbean, and Latin America.[144] The larva is 400– 1,000 ì m long[145] and is widely known as the cutaneous larva migrans.[146]

The second nematode is believed to be the raccoon worm, Baylisascaris procyonis,[143,147] a nematode that is most frequently found in the Northern and Midwestern United States.[148,149] It is 1,000–2,000 ì m long, and this worm is the most common cause of cutaneous and visceral larva migrans in animals.[148] The transmission occurs through accidental ingestion of infective eggs through feces or other contaminated materials.[141]

The initial presentation is typically unilateral vision loss, with central or paracentral scotoma. Approximately half of affected patients, however, do not notice this vision loss; thus, they often come to medical attention with advanced stages of disease. Ocular discomfort is less frequently seen in the early stages of the disease. The pathogenesis of the development of the inflammation in the fundus is not known but may arise from toxic by-products or egested waste material causing an immune response in the host.[150]

The disease is usually unilateral, but bilateral manifestations have also been reported.[139,151] Nematodes can affect both eyes, and, in addition, more than one nematode can be observed in one eye.[151,152] The clinical findings are similar between the different nematodes. Although patients with hypopyon have been reported,[94,153] extensive anterior segment inflammation is not common.

Funduscopic examination reveals multiple grayish-white lesions in the deep retina in the early phases of the disease. Narrowing of the arterioles was noted in approximately half of the patients.[94] Focal and widespread pigmentary changes may occur and include white spots, focal hyperpigmentation, diffuse alterations of pigmentation, and subretinal fibrosis. Vitritis and papillitis are characteristic findings of DUSN.[138]

Other clinical findings include afferent papillary defects, optic nerve edema, optic atrophy, and CNV.[43,139] In the late stages of disease, the extensive amount of intraocular damage may be so severe that the examiner may not initially think to look for a small nematode.

Color fundus photography or scanning laser ophthalmoscopy with blue light are helpful to locate the nematode. Careful inspection of serially acquired images of as much of the fundus as possible may be necessary to locate the nematode.[154] Examination of fundus photographs is often times more fruitful than looking for the nematode using a contact lens. Once the region wherein the nematode exists is found, the patient can have a directed examination with a contact lens to make visual sighting. The fluorescein angiographic results in DUSN can be quite variable. There may be leakage from the retinal vessels and staining of the optic nerve. Diffuse retinal leakage and edema can be seen. There are transmission defects in regions of RPE atrophy and blocking defects where there is increased pigmentation[138] that does not directly correspond to the active lesions.[155] Angiography is not helpful to localize the nematode.[156]

The ERG results show pathological changes and decreased activity but are rarely extinguished.[94,138] Systemic evaluation using serological tests for parasites, stool evaluation for ova and parasites, and hematological screenings for eosinophilia is of limited value.[143] Serological tests might be indicated to rule out other diseases. The anamnesis may be important to evaluate contact with soil and animals, such as raccoons, to support the diagnosis.[143,147,149]

Thermal laser photocoagulation of the nematode is the first choice for treatment. This option effectively destroys the worm.[157] Thermal laser photocoagulation can even be successful if no worm was detectable. In this case, the suspected localization of the nematode should be treated.[158] Treatment with antihelminthic drugs has been reported to be both effective and ineffective.[5,138,159,160] Surgical extraction, either transclerally or transvitreally, may be appropriate in young children who cannot tolerate laser photocoagulation.[138,161,162] However, vitrectomy entails longterm complications, such as an increased rate of cataract formation.

The prognosis of the visual acuity is often poor, as patients frequently present after they have had substantial loss of vision.[159,163]

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