Teaching Case

A 19-year-old male presented with a history of numbness of both lower limbs and difficulty in walking for 2 days with progressive involvement of both upper limbs. There was also blurring of vision in the left eye. On examination, there was reduced sensation in both upper and lower limbs with an ataxic gait.

3 Tesla MRI of Brain & spine was done which showed long segment intramedullary T2 hyperintensities in the spinal cord extending from the cervico-medullary region to D1 level (Fig 1,2), with expansion of the cervical cord. Subtle intramedullary T2 hyperintensities were also noted in the lower dorsal cord and conus medullaris (Fig 2). The hyperintensities were seen predominantly involving the central and posterior parts of the spinal cord with relative sparing of the anterior portion (Fig 4). Post-contrast administration, the cervico-dorsal lesion showed patchy enhancement (Fig 5). The nerve roots of the cauda equina appeared normal. Discrete T2 hyperintensities were also noted in the left anterior midbrain (Fig 6). Both optic nerves appeared relatively thickened with T2/ STIR hyperintensities in the left optic nerve (Fig 3,7). Based on the above finding, the possibility of neuromyelitis optica spectrum disorder (NMOSD) was suggested and the patient was subjected to laboratory workup for the same.

Nerve conduction study was done which showed a mild delay in latencies. CSF analysis showed a total count of 60 cells with lymphocyte predominance, glucose - 86 mg/dl, and protein - 51.1mg/dl. CSF Anti-MOG (Myelin oligodendrocyte glycoprotein) antibody was positive. NMO Antibody (Serum and CSF) and oligoclonal bands were negative. The patient was treated with intravenous immunoglobulin & Azathioprine following which his symptoms gradually improved.

Repeat MRI brain and spine was done after 2 weeks. In comparison with the previous study, the follow-up scan showed a significant reduction in the cervico-dorsal intramedullary T2 hyperintensities (Fig 8,9) and relative reduction in the size of the left midbrain T2 hyperintensity (Fig 10), reflecting a good response to treatment.

Neuromyelitis optica spectrum disorders are demyelinating disorders associated with attacks on the optic nerves and spinal cord. The presence of an NMO-specific antibody (Anti-aquaporin 4) in the CSF and serum has allowed these patients to be distinguished from those with multiple sclerosis [1]. However, some patients with clinical presentations suggestive of NMOSD do not show anti-aquaporin 4 antibodies. In these patients, autoantibodies against myelin oligodendrocyte glycoprotein (MOG-IgG) have been identified. Myelin oligodendrocyte glycoprotein (MOG) is a glycoprotein located on the myelin surface and found exclusively in the central nervous system [2]. MOG antibody disease is now recognized as a distinct clinical entity with specific management and therapeutic requirements.

MOG Antibody associated disease is an inflammatory demyelinating disorder characterized by the presence of IgG antibodies to myelin oligodendrocyte glycoprotein. It has overlap with acute disseminated encephalomyelitis (ADEM), neuromyelitis optica spectrum disorder (NMOSD), and multiple sclerosis (MS) [3,4]. It is also known by several other terminologies like MOG-IgG-associated Optic Neuritis, Encephalitis, and Myelitis (MONEM), Anti-MOG associated encephalomyelitis, and anti-MOG encephalitis.

Features suggestive of MOG Antibody Disease as opposed to NMOSD include male gender, single or few attacks, bilateral or recurrent optic neuritis sparing the optic chiasma, LETM involving the conus medullaris, and good recovery after attacks [5]. Recovery from attacks is also reported as better in MOG Antibody Disease than in AQP4-IgG-seropositive NMOSD [6].

Radiologically it is difficult to differentiate between NMOSD & MOG Antibody Disease with certainty but there are some imaging features that can help to point towards a certain diagnosis. Both patient groups show cervical myelitis as the most frequent spinal cord involvement, but lumbosacral myelitis is more common in patients with anti-MOG-Ab. While patients with AQP4-IgG usually present cervical (with or without brainstem involvement) and thoracic lesions, patients with MOG-IgG may present lesions of the lower cord, including the conus medullaris [7]. However, in our case, the cervical cord was more extensively involved. Recent reports have mentioned T2 hyperintensity confined to grey matter in a sagittal T2-hyperintense line and forming axial H sign was a radiologic clue to MOG-IgG myelitis [8]. Central and posterior grey matter  involvement  as noted in our patient may reflect  gray matter demyelination in MOG-IgG–related disease.

Bilateral, longitudinally extensive, symmetrical optic neuritis in the intra-orbital segments with sparing of the optic chiasma is characteristic of MOG antibody disease [9,10].

MRI Brain in MOG antibody disease shows thalamic and pontine lesions. Supratentorial deep white matter lesions and a small number (≤3) of poorly demarcated infratentorial lesions may also be seen. Some patients may also develop brainstem lesions as seen in our case. However, the brainstem lesions here are small and poorly demarcated as compared to the brainstem lesions in MS. Rarely, medullary lesions may be seen, presenting as area postrema syndrome with intractable hiccups, like that seen in NMSOD. Also, children tend to show a higher number of lesions, bilateral lesions, and larger lesions, especially in the deep grey matter and brainstem.

The management of acute attacks usually includes the same strategies used for other CNS immune-mediated conditions, such as oral or intravenous methylprednisolone (IVMP), plasma exchange, intravenous immunoglobulin (IVIg), and cyclophosphamide [11].

MOG Antibody Disease exhibits different pathophysiological and imaging features from both AQP4-IgG-associated NMOSD and typical MS. Radiologically it has overlap with NMOSD but preferential involvement of the conus, predominant retrobulbar optic nerve involvement, and thalamic and pontine involvement helps in differentiation.

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