Description

A 47-year-old man presented with rapid deterioration in vision and painful eye movements of his left eye. Two years prior he had been diagnosed with frontal left demyelinating lesion by MRI and biopsy after presenting with subacute, though rapidly progressive, right hemiparesis. His neurological deficit worsened despite the treatment with intravenous methylprednisolone and intravenous immunoglobulin, but subsequently responded to intravenous rituximab. He was clinically stable over the 2 years leading up to current presentation, with MRI that showed the residual right frontal lesion, but no other or interval lesions in the brain or spinal cord. He was presumptively diagnosed with acute disseminated encephalomyelitis.

On initial examination after the onset of his visual symptoms, he was only able to perceive light with the left eye, unable to count fingers. He had a positive relative afferent papillary defect on the left, and was clinically diagnosed with acute optic neuritis. MRI (figure 1) performed 5 days after the symptoms onset revealed high T2-weighted signal of the left optic nerve with evidence of diffusion restriction and apparent diffusion coefficient (ADC) reduction in the corresponding location.

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Figure 1

Diffusion-weighted imaging (DWI) and apparent diffusion coefficient (ADC) view of left acute optic neuritis. DWI (left) and ADC (right) images show left optic nerve high DWI signal (left arrow) with corresponding low ADC (right arrow), consistent with acute ischaemia as can be seen with acute demyelinating lesions.

The patient's visual loss remained permanent despite treatment with pulsed methylprednisolone followed by a weaning course of oral prednisolone. Over the next 6 months, he had suffered from four more episodes of acute visual deterioration affecting his right eye. Diffusion restriction and ADC reduction were not demonstrated; however, he did have interval development of high short T1 inversion recovery (STIR) signal associated with contrast-enhancement in the right optic nerve (figure 2). There was persistence of high STIR signal in the left optic nerve (figure 2), this may represent ongoing inflammation or scar tissue formation. This is difficult to differentiate in the absence of new symptoms affecting the left eye in the context of extremely poor visual acuity. The loss of right-sided visual acuity was refractory to treatment with methylprednisolone, rituximab and plasma exchange. Subsequently, monthly intravenous cyclophosphamide was started, and as a result he remained disease free for 4 months and had some minimal improvement in right-sided visual acuity. Imaging of patient's spine demonstrated no cord abnormality.

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Figure 2

Short T1 inversion recovery (STIR) view of the bilateral optic nerve (subsequent episode). The STIR image showing high signal in the bilateral optic nerves (arrows) consistent with right optic neuritis (supported by symptom). Left optic nerve high signal could be secondary to optic neuritis or scar tissue formation.

The results of the tests for antiaquaporin-4 (AQP4) and antimyelin oligodendrocyte glycoprotein antibodies were negative. However, the clinical picture was most consistent with neuromyelitis optica (NMO) spectrum disorder. Patients with relapsing disease NMO spectrum disorder tend to have a long interval between the first index event and first relapse.1 The first relapse is then followed by a cluster of severe relapses usually involving the optic nerve or the spinal cord, which recover poorly despite treatments. This leads to cumulative morbidities in vision and motor function.1 Bilateral optic neuritis is also more suggestive of NMO spectrum disorder.2

Diffusion-weighted imaging is the best method to identify ischaemic lesions in the brain. Uncommonly, acute optic neuritis can also cause diffusion restriction and reduced ADC value in the optic nerve.3 It is unclear from the literature whether this would be a distinguishing feature between acute optic neuritis secondary to multiple sclerosis or NMO spectrum disorder.