Wriggly worm in the eye: Diffuse unilateral subacute neuroretinitis

A man in his 40s presented with a four-day history of vision loss in his right eye, with visual acuity in the right eye reduced to hand motion. Anterior segment evaluation was unremarkable. On retinal examination, there was a hyperemic optic disc with mild disc edema, multifocal yellowish-white macular lesions, and a live, motile worm in the macula, accompanied by neurosensory detachment seen on optical coherence tomography [Fig. 1a and b]. Optical coherence tomography angiography (OCTA) confirmed the presence of the worm in the subretinal space [Fig. 1c]. Based on these findings, a diagnosis of diffuse unilateral subacute neuroretinitis (DUSN) in the right eye was established.

Figure 1.

(a) Color fundus photograph of the right eye showing the live motile worm at the macula (white arrow). Small multifocal yellowish lesions are noted (yellow arrow) near the worm and along the inferotemporal arcade. (b) OCT shows the presence of large subfoveal neurosensory detachment (red arrow) with hyperreflectivity of the worm. (c) OCTA from deep slab showing the coiling nature of worm in the subretinal area

What will be your preferred line of management?

1. Focal laser

2. Oral antihelminthic

3. Oral steroids

4. All the above.

Diagnosis: Acute stage of diffuse unilateral subacute neuroretinitis with live motile worm

Correct Answer: D. All the above

Discussion

DUSN is an infectious ocular disease caused by motile nematodes. The first report of nematode infection in the eye was documented by Wilder in 1950 in an enucleated eye specimen.[1] In 1978, Gass and Scelfo[2] formally described DUSN as a clinical entity after identifying a worm in 2 of 36 cases with similar clinical presentations. Nematodes implicated in previous cases include Toxocara canis, Baylisascaris procyonis, and Ancylostoma caninu.[3,4]

In the acute stage, DUSN typically presents with unilateral vision loss, mild vitritis, and papillitis, along with recurrent crops of transient gray-white outer retinal lesions. Early-stage DUSN can be misdiagnosed as multifocal choroiditis, acute posterior multifocal placoid pigment epitheliopathy (APMPPE), multiple evanescent white dot syndrome (MEWDS), or nonspecific optic neuritis.[5] The chronic stage is characterized by optic atrophy, diffuse retinal pigment epithelium changes, visual field constriction, and abnormal electroretinogram findings.

Treatment options include anti-helminthics, focal laser therapy, and oral steroids.[6,7] Focal laser photocoagulation promotes the aseptic breakdown of the blood-retinal barrier (BRB), enhancing the penetration of antihelminthic agents. Thiabendazole and corticosteroids have demonstrated efficacy in cases with moderate vitreous inflammation and BRB disruption, particularly when the worm is not visible. Gass and Olsen previously advocated for scatter photocoagulation near white lesions to induce BRB breakdown, thereby optimizing the effectiveness of thiabendazole. Subsequently, oral albendazole, a broad-spectrum antihelminthic capable of crossing the BRB with minimal systemic side effects, was investigated for DUSN. It exerts its action by binding to parasite beta-tubulin, inhibiting polymerization, and impairing glucose uptake. While the optimal dosing and duration for DUSN remain undetermined, a 30-day regimen has been proposed based on favorable outcomes in neurocysticercosis.[8]

In this case, focal laser therapy was employed to target and eliminate the worm. However, due to the worm’s mobility and its macular location, only a few extrafoveal laser burns were applied to outer retinal lesions to disrupt the BRB. The patient was also treated with oral albendazole (400 mg once daily for one month). Complete resolution was achieved within three weeks, with significant visual improvement to 6/36.

Conflicts of interest

There are no conflicts of interest.

Funding Statement

Nil.