Abstract
Purpose
To describe a case of diffuse unilateral subacute neuroretinitis (DUSN), a rare condition that causes progressive vision loss following infection by a nematode using enface vitreous imaging.
Observations
We present the clinical findings of a 37-year-old female, clinically diagnosed with DUSN after a non-invasive multimodal imaging approach that included MultiColor scanning laser imaging and enface vitreous OCT, which revealed the nematode body and lacunae created by worm migration, respectively.
Conclusion and importance
To our knowledge, this is the first reported case of lacunae visualized using enface vitreous optical coherence tomography (OCT), potentially marking the migration path of the nematode.
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Introduction
Diffuse unilateral subacute neuroretinitis (DUSN) is a rare, ocular infectious disease caused by infection by a nematode that can lead to severe visual impairment and blindness. It primarily presents unilaterally, however bilateral cases have been previously reported. DUSN typically occurs in young, otherwise healthy, individuals, a finding Gass noted when he first described the disease in 1977.
Previously termed unilateral wipeout syndrome, DUSN presents with: “(1) insidious, usually severe loss of peripheral and central vision; (2) vitritis; (3) diffuse and focal pigment epithelial derangement with relative sparing of the macula; (4) narrowing of the retinal vessels; (5) optic atrophy; (6) increased retinal circulation time; (7) subnormal electroretinographic findings.” Given the aforementioned clinical features, DUSN can often masquerade as optic neuritis, pars planitis, histoplasmosis, toxoplasmosis, syphilitic chorioretinitis, sarcoidosis, acute posterior multifocal placoid pigment epitheliopathy, choroidal macrovessel and multiple evanescent white dot syndrome (MEWDS) in the early stages as well as unilateral retinitis pigmentosa, occlusive vascular disease, toxic retinopathy, and posttraumatic chorioretinopathy in the late stages.
In 60–75% of cases, the nematode is not visualized and thus surgical or laser intervention is not possible. In patients where the worm is not observed, treatment with oral anthelmintic drugs, such as albendazole, can be used, but according to previous reports only some of the subretinal worms were destroyed due to differences in the blood-retinal barrier breakdown of the inflamed eye. We describe a case of DUSN evaluated using multi-modal imaging, where the nematode was visible, following MultiColor scanning laser imaging, on the internal limiting membrane (ILM). Enface vitreous optical coherence tomography (OCT) further revealed lacunae, which may represent areas of worm movement (“worm holes”). To our knowledge this has not been previously reported and may aid in the visualization of nematodes in suspected DUSN cases.
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Case report
A 37-year-old female with sudden vision loss in the left eye was referred for possible MEWDS. The patient works as a social media manager and had no past medical or ocular history that was pertinent to this case. There was no family history of any ocular or genetic diseases. In November 2019, the patient travelled to Lahore, Pakistan where she consumed street food that contained beef, chicken and fish. The meat was either grilled or fried and no uncooked or raw meat was consumed. The patient returned home to Toronto in January 2020, asymptomatic from her travel. In May 2020, the patient was gardening and handled racoon feces, while wearing disposable gloves. Within one month, the patient noticed sudden decreased vision in the left eye. Her best-corrected visual acuity (BCVA) was 20/20 OD and CF OS. Anterior segment examination was unremarkable. Afferent pupillary defect was noted OS. The right eye was normal. Fundus examination revealed the presence of 1+ vitreous cells in the left eye with a normal appearing disc, the macular and posterior pole demonstrated diffuse non-specific retinal pigment epithelium (RPE) changes and normal appearing retinal vessels. OCT revealed nerve fibre layer (NFL) thinning in the affected eye. No obvious change in the choroid was noted.
Initially, color fundus photography and OCT was performed, but the nematode was not visible. Fundus autofluorescence (FAF) (Optos California; Optos PLC; Dunfirmline, UK) demonstrated both focal and pinpoint hyper-and hypo-autofluorescent dots in the posterior pole and along the arcade, but did not show a nematode body. MultiColor scanning laser imaging (Heidelberg Spectralis HRA + OCT MultiColor; Heidelberg Engineering, Inc., Heidelberg, Germany) revealed the nematode body ( Fig. 2 A), which was observed in the green reflectance (GR) and blue reflectance (BR) images ( Fig. 2 C&D), while near-infrared reflectance (NIR) did not show the worm ( Fig. 2 E). Subsequent color fundus photography (Topcon TRC 50-DX) revealed a subretinal nematode in the inferotemporal quadrant of the left eye ( Fig. 1 A–D ). Enface OCT (Heidelberg Spectralis HRA + OCT) segmented at the ILM demonstrated the nematode atop the ILM in a coiled position ( Fig. 3 A), which is incompletely visible in the corresponding transverse SD-OCT images ( Fig. 3 B). Enface swept-source OCT of the vitreous (Plex Elite 9000; Carl Zeiss Meditec, Germany) revealed hyper-reflective dots suggestive of vitreous cells and several opaque small lacunae temporally and inferotemporally suggestive of, what we would term, “worm holes” ( Fig. 5 ). These worm holes are potentially areas where the nematode traversed through the vitreous.
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