We report on the first known case of diffuse unilateral subacute neuroretinitis (DUSN) found in Asia. It is important for physicians in those areas in which DUSN has been described to remain vigilant in looking for its occurrence as well as being aware of its possibility in regions in which it has not yet been identified as endemic.
A 24-year-old Chinese woman was first seen at the Department of Ophthalmology, Shanghai ChangZheng Hospital, September 15, 1998, with the complaint of a 2-week history of painless progressive loss of vision in her left eye. Her ocular history was unremarkable. On examination she was found to have a best-corrected visual acuity of 20/20 OD and 20/200 OS (her affected eye). There was no pallor of the left optic disc and no apparent arteriolar attenuation; however, a left relative afferent pupillary defect was present. Diffuse, small patchy retinal pigment epithelium changes with 2+ cells in the vitreous and a decreased macular reflex were present. Intraocular pressure was normal. Absence of a pattern visual evoked potential was noted and the flash visual evoked potential response was positive in the left eye. The right eye was normal.
On September 22, 1998, while the patient was being examined, a motile white worm was seen about 1.5 disc diameters inferior to the fovea. It was approximately 1500 µm long and 80 µm wide. The following day the worm was found inferonasal to the optic disc with its head and tail embedded more deeply in the retina. The nonsegmented cylindrical nematode just overlay the vein with an S-shaped configuration (Figure 1) and accompanying hemorrhage. One week later, the hemorrhage was absorbed and the nematode changed to a V shape (Figure 2).
September 23, 1998. Nematode with an S-shaped configuration seen in the shallow portion of the retina of the left optic disc, 1.5 disc diameters inferior to the fovea over the inferonasal branch vein with hemorrhage.
One week later from Figure 1, the nematode's appearance has changed to a V shape, with its head and tail more deeply embedded in the retina. The hemorrhage has cleared.
The patient was born and raised in an urban area (Shanghai, China) with no experience of close contact with cats, dogs, or raccoons. She had never ingested raw fish nor had she drunk fresh water. No skin lesions or changes could be found. Results of a complete blood cell count with differential cell count were within normal ranges, with no eosinophilia. No worm or egg was found in her stool. Findings from a magnetic resonance imaging scan of the orbit and brain were normal. Fluorescein angiograghy of the left eye demonstrated scattered small areas of irregular hyperfluorescence with leakage near the nematode.
Laser photocoagulation (focal Argon green) was applied on October 15, 1998. The patient was followed up for more than 11 months without recurrence of the inflammation. Her best-corrected visual acuity in the affected left eye has remained 20/200. No other parasites were noted. The area of laser photocoagulation demonstrated evidence of chorioretinal scarring.
Diffuse unilateral subacute neuroretinitis is typically characterized by progressive visual loss secondary to inflammatory changes in the retinal pigment epithelium, retinal vessels, and optic nerve. It usually affects young healthy individuals. Evidence exists that DUSN is caused by infestation of a solitary intraretinal or subretinal nematode1,2 whose exact identity remains uncertain. Several species of nematodes, including Toxocara canis, Baylisascaris procyonis,3 and Ancylostoma caninum have been suggested as the potential etiologic agent of DUSN.
The nematodes have been classified into 2 different sizes. The smaller nematode, measuring 400 to 1000 µm in length, is endemic to the southeastern United States, the Caribbean islands, and Brazil. The larger nematode, measuring 1500 to 2000 µm in length, has been described in the northern midwestern United States.2
Toxocara canis and B procyonis are the most common causes of internal larva migrans in animals and humans, and either parasite could be involved in human ocular larva migrans and DUSN. Morphologically, the nematode in this case appears to be a large one and is most likely B procyonis. To our knowledge, this is the first reported case of DUSN occurring in Asia.
Accurate diagnosis of the disease is important because destruction of the worm in early stages will halt the progression of visual loss. Observation and destruction of the nematode are the methods of choice for accurately reaching a diagnosis and treating patients with DUSN. Medical treatment is generally believed to be ineffective because of the relative impermeability of the blood-retinal barrier. A recent report confirmed this.4 Laser treatment remains an effective means of treatment.
Corresponding author: Jiping Cai, MD, Department of Ophthalmology, ChangZheng Hospital, The Second Military Medical University, 415 FengYang Rd, Shanghai 200003, People's Republic of China (e-mail: email@example.com).
Cai J, Wei R, Zhu L, Cao M, Yu S. Diffuse Unilateral Subacute Neuroretinitis in China. Arch Ophthalmol. 2000;118(5):721–722. doi:
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