Objectives To describe 2 cases of anti-MOG demyelinating disease presenting as NMO.
Methods We reviewed the medical records of 2 patients seen at Nelson Hospital with bilateral optic neuritis, one with transverse myelitis.
Cases A 23 years old man developed truncal paraesthesias followed 24 hours later by bilateral visual loss, sphincter disturbance, saddle anaesthesia and imbalance. Treatment with methylprednisolone (MP) resulted in minimal improvement followed by therapeutic plasma exchange with return to normal. CSF showed 50 white cells with normal protein, negative OCB’s and normal IgG index. Brain and optic nerve MRI was reported as normal but there was longitudinally extensive, non-enhancing thoracic cord T2 hyperintensity. IgG antibodies to aquaporin-4 (NMO-IgG) were negative but MOG antibodies were positive. A 54 years old woman developed bilateral severe visual loss and paraesthesias in the right foot which rapidly resolved with MP but recurred one month later, again successfully treated with MP. CSF showed 10 white cells with normal protein, negative OCB’s and normal IgG index. MRI showed bilateral optic nerve enhancement and an enhancing pontine lesion. Cord MRI done a month later was normal. NMO-IgG was negative but MOG antibodies were positive.
Conclusions Simultaneous or sequential bilateral optic neuritis and transverse myelitis is the characteristic phenotype of NMO. About 75% of such patients have NMO-IgG. The remainder are seronegative but meet clinical and MRI criteria for the disease and are classified as NMO-spectrum disorder (NMO-SD). We describe two patients who presented with a characteristic clinical phenotype who were seronegative for NMO-IgG but had antibodies to MOG. It has been suggested that this constitutes a unique disorder and should not be classified as part of NMO-SD. This distinction is of practical importance since CNS demyelinating patients with antibodies to MOG has a better prognosis than typical NMO and treatment may be different.
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