Case of the Month

Edited by Robert N. Johnson, MD

Figure 1: Color photo montage of the right eye. Note the optic disc pallor, attenuated retinal arterioles, areas of retinal whitening in the nasal and peripapillary macula, sub- and parafoveal fibrotic changes, and diffuse RPE atrophy.

Case History

A 49-year-old Latino male presented with the complaint of decreased vision in the right eye for 2 months. Past ocular history was notable for retinochoroiditis of unclear etiology in the right eye, and prior work up performed elsewhere had included negative QuatiFERON-TB Gold test, non-reactive rapid plasma reagin test, and normal complete blood count. Upon presentation, he was taking 80 mg per day oral prednisone for ocular inflammation. Past medical history was unremarkable aside from systemic hypertension, treated with lisinopril. Family history was non-contributory. Upon review of systems the patient said he had experienced diffuse urticaria 1 month prior to presentation. Occupational history included current work as a tree-trimmer in Northern California.

On examination, visual acuity was hand motions in the right eye and 20/16 in the left eye. There was an afferent pupillary defect in the right eye. Ocular motility, intraocular pressure, and anterior segment examinations were normal in both eyes.

The posterior segment examination of the right eye revealed moderate vitritis, optic disc pallor, attenuated retinal vessels, areas of retinal whitening in the nasal macula, and diffuse retinal pigment epithelium (RPE) atrophy (Figure 1). Dilated examination of the left fundus was unremarkable.

Wide-field fundus autofluorescence of the right eye showed diffuse mottled hyper- and hypoautofluorescence predominantly in the posterior pole (Figure 2), and widefield fluorescein angiography revealed extensive hyperfluorescence from RPE window defects (Figure 3). Optical coherence tomography (OCT) scan of the right eye revealed extensive atrophy the retinal layers and RPE and a prominent internal limiting membrane (Figure 4).

Figure 4: Optical coherence tomography (OCT) scan of the right eye: Note the extensive atrophy the retinal layers and RPE and a prominent internal limiting membrane.

Differential Diagnosis

Multifocal choroiditis, acute posterior multifocal placoid pigment epitheliopathy, serpiginous chorioretinopathy, sarcoidosis-associated chorioretinitis, diffuse unilateral subacute neuroretinitis, toxoplasmosis retinochoroiditis, intraocular lymphoma.

Additional History and Clinical Course

Upon closer inspection of the macula, a motile intraretinal worm (2500 microns x 100 microns) was identified (Figure 5), confirming the diagnosis of diffuse unilateral subacute neuroretinitis. The worm was also visible on OCT-angiography (Figures 6a and 6b). Given the size of the worm, the presumed species was Baylisascaris procyonis. The worm was promptly photocoagulated with argon laser. The patient was given a 4-week course of oral albendazole and the steroids were tapered. At 1.5 year follow up, the right eye remained quiet and vision was stable at hand motions.

Figure 5: Magnified color photo of the right eye. Note the intraretinal worm located superotemporally.

Discussion

 Diffuse unilateral subacute neuroretinitis (DUSN) was first described by Gass and Scelfo in 1978.¹ It is a syndrome characterized by widespread unilateral posterior ocular inflammation secondary to a motile sub- or intraretinal nematode worm. Before recognition of the worm as the etiologic agent, the spectrum of clinical findings was referred to as “unilateral wipe-out syndrome”.

 DUSN is uncommon, and most typically unilateral and diagnosed in young individuals.² It can present in early and late stages. In early stages, the syndrome is characterized by vitritis, disc edema, multiple grey-white outer retinal lesions, and retinal pigment epithelial changes. These findings may be misdiagnosed as idiopathic inflammatory or other infectious posterior uveitis. Late stage findings include disc pallor, vascular attenuation, and extensive retinal pigment epithelial atrophy, and are sometimes misdiagnosed as unilateral retinitis pigmentosa, the presumed ocular histoplasmosis syndrome, post-traumatic chorioretinopathy, or toxic retinopathy.

 The diagnosis of DUSN is confirmed by the identification of a motile subretinal worm on clinical exam. However, this can be difficult, and rates of worm detection in DUSN cases range from 33-52%.² Contact lens fundus examination and fundus photography are helpful. As this case demonstrates, OCT-angiography (OCT-A) may also have some utility in identification of the worm. Since nematode worms are avascular, detection on OCT-A is likely due to worm movement.³

Previous reports of DUSN have typically shown two different size ranges of causative worms which appear to correspond to geographic region: a smaller worm (400-1000 microns) mostly seen in the southeastern US, and a larger worm (1500-2000 microns) mostly seen in the northern and midwest US.² Serologic evidence suggests that the larger worm is Baylisascaris procyonis. The species of the smaller worm is less definitive, but Ancylostoma caninum and Toxocara canis (both common parasites of dogs) are considered likely culprits. McDonald and colleagues have also reported DUSN secondary to the trematode Alaria mesocercaria.⁴

B. procyonis, the likely culprit in this case, is an intestinal nematode of raccoons. In addition to DUSN, it has also been associated with devastating meningoencephalitis in humans.⁵ Risk factors for B. procyonis infection are contact with raccoon feces or an environment contaminated with infective B. procyonis eggs. Raccoons are known to habitually defecate in communal areas including on stumps and near trees, and are particularly common in Northern California.⁶ The patient’s work as a tree-trimer in this geographic region, therefore, likely put him at risk.

The treatment of DUSN is with photocoagulation of the worm. In cases where DUSN is strongly suspected but the worm cannot be visualized, a course of antihelminthic (albendazole) can be tried, which may lead to cessation of inflammation and some visual recovery.⁷

This Case of the Month was adapted from the article “Optical coherence tomography angiography of diffuse unilateral neuroretinitis” by Ananda Kalevar and J. Michael Jumper, published in America Journal of Ophthalmology Case Reports on June 22, 2017.

References

1. Gass JD, Gilbert WR, Guerry RK, Scelfo R. Diffuse unilateral subacute neuro- retinitis. Ophthalmology. 1978;85:521-545.
2. Ávila, M, Isaac, D. Helminthic Disease. In: Ryan SJ, Schachat AP, Sadda SR, eds. Retina. Fifth ed. Elsevier:1500-1514.
3. Kalevar A, Jumper JM. Optical coherence tomography angiography of diffuse unilateral subacute neuroretinitis. Am J Ophthalmol Case Reports 2017;7:91-94.
4. McDonald HR, Kazacos KR, Schatz H, Johnson RN. Two cases of intraocular infection with Alaria mesocercaria (Trematoda). Am J Ophthalmol. 1994;117: 447-455.
5. Gavin PJ, Kazacos KR, Shulman ST. Baylisascariasis. Clin Microbiol Rev. 2005;18:703-718.
6. Roussere GP, Murray WJ, Raudenbush CB, Kutilek MJ, Levee DJ, Kazacos KR. Raccoon roundworm eggs near homes and risk for larva migrans disease, California communities. Emerging Infectious Diseases. 2003;9:1516-1522.
7. Souza EC, Casella AM, Nakashima Y, Monteiro ML. Clinical features and outcomes of patients with diffuse unilateral subacute neuroretinitis treated with oral albendazole. Am J Ophthalmol. 2005;140:437-445.