Multifocal electroretinography in dengue fever‐associated maculopathy

Dengue fever is a viral disease transmitted by Aedes mosquitoes and is endemic in the tropics.¹ The severity of dengue fever varies from mild non‐specific febrile illness to potentially fatal dengue haemorrhagic fever causing thrombocytopenia and shock. Patients with dengue fever may develop various ophthalmic manifestations causing visual loss, including macular oedema, macular haemorrhage, retinal vasculitis, “cotton‐wool” spots and optic disc swelling.²,³,⁴,⁵,⁶,⁷,⁸ We report the use of multifocal electroretinography (mfERG) in the assessment of a patient with dengue fever‐associated maculopathy in whom there were no clinical or angiographic abnormalities.

Case report

A 16‐year‐old girl with serologically confirmed dengue fever presented with left relative scotoma and reduced vision 7 days after the onset of fever. Her visual acuity was 20/20 and 20/40 in the right and left eye, respectively. Anterior segment examination was unremarkable. Fundus examination showed no abnormality and particularly no retinal haemorrhage. Optical coherence tomography demonstrated normal foveal depression and retinal thickness. Fluorescein and indocyanine green angiographies showed no abnormal leakage (fig 1). Owing to the lack of clinical evidence of maculopathy, mfERG was performed to evaluate the macular function. mfERG demonstrated reductions in both N1 and P1 response amplitudes at the central and nasal macula, corresponding to the scotoma on perimetry (fig 2). The patient was managed conservatively without treatment. After 1 year, her visual acuity remained at 20/40 with absence of fundus abnormality. Repeat mfERG recording showed persistent response abnormalities.

Figure 1 (A) Mid‐phase fluorescein angiography and (B) mid‐phase indocyanine green angiography of the left eye showing normal retinal and choroidal vasculature and the absence of abnormal hyperfluorescence, hypofluorescence or blocked fluorescence at the macula.

Figure 2 (A) 30–2 Humphrey visual field of the left eye showing a centrocoecal scotoma. (B) Trace array of multifocal electroretinography showing reduction in the retinal responses at the central and nasal macula (grey area) corresponding to the area of the scotoma.

Comment

Ocular manifestations in dengue fever have been reported in several case series, and the commonest fundus findings are retinal haemorrhage and macular oedema.²,³,⁴,⁵,⁶,⁷,⁸ The onset of visual symptoms usually coincides with the resolution of fever and the lowest point of thrombocytopenia.⁶,⁷,⁸ In our patient and in previous reports, the interval between fever onset and ophthalmic symptoms was around 7 days.²,⁶,⁷,⁸ It has been postulated that this time interval corresponds to the time of antibody formation, deposition of immune complexes or production of autoantibodies.⁶

Visual disturbances in dengue fever‐associated maculopathy were suggested to be because of retinal haemorrhages, or retinal and choroidal vasculopathy.⁶,⁷,⁸,⁹ In our patient, visual loss developed in the absence of fundus abnormality including retinal haemorrhages or oedema, and without any angiographic abnormality. With the use of mfERG, retinal dysfunction in the central and nasal macula corresponding to the scotoma was detected. As both the N1 and P1 responses were reduced, the findings suggested that dengue fever‐associated maculopathy might be due to damage to the photoreceptors or bipolar cells. After 1 year, the mfERG abnormalities were found to be persisting in the absence of any visible fundus changes.

Our mfERG and clinical findings support the hypothesis that formation of autoantibodies against the retina could cause visual loss in dengue fever‐associated maculopathy, and that the functional changes could be irreversible. A similar clinical picture and mfERG findings may also occur in acute zonal occult outer retinopathy,¹⁰ and dengue fever‐related maculopathy could therefore be an acute zonal occult outer retinopathy‐like disorder. The use of mfERG enabled the diagnosis of dengue fever‐associated maculopathy, which would otherwise be difficult to confirm in the absence of clinical or angiographic abnormalities.