myelin_oligodendrocyte_glycoprotein_antibody-associated_optic_neuritis

Myelin oligodendrocyte glycoprotein antibody-associated optic neuritis

Myelin oligodendrocyte glycoprotein antibody-associated optic neuritis (MOG-ON) is a subtype of optic neuritis associated with the presence of antibodies against myelin oligodendrocyte glycoprotein (MOG), a protein located on the surface of myelin in the central nervous system. MOG-ON is part of the broader condition known as MOG antibody-associated disease (MOGAD), which can present with various neurological symptoms, including optic neuritis, transverse myelitis, and encephalitis.

### Key Features of MOG-ON: - Pathophysiology: The immune system mistakenly produces antibodies against MOG, leading to inflammation and damage to the myelin in the optic nerves and other parts of the CNS. This results in demyelination and impaired nerve signal transmission.

### Clinical Presentation: 1. Optic Neuritis:

  1. Bilateral or Unilateral: MOG-ON often presents bilaterally (affecting both eyes) but can also be unilateral.
  2. Pain with Eye Movement: Common symptom during acute attacks.
  3. Vision Loss: Moderate to severe visual impairment during attacks. Recovery is often better than in other types of optic neuritis, but relapses may occur.
  4. Recurrence: MOG-ON tends to have a relapsing course, and patients may experience multiple episodes of optic neuritis.

2. Other Symptoms in MOGAD:

  1. Transverse Myelitis: Inflammation of the spinal cord, leading to weakness, sensory changes, and bladder/bowel dysfunction.
  2. Encephalitis: Rare, but when it occurs, it typically affects the brainstem and can cause nausea, vomiting, and other brainstem symptoms.

### Differences between MOG-ON and AQP4-ON (NMOSD): MOG-ON and aquaporin-4 antibody-positive optic neuritis (AQP4-ON) (seen in NMOSD) can present similarly but have important differences: - Relapse Frequency: MOG-ON tends to relapse, but the relapses may be less severe and recovery is generally better compared to AQP4-ON. - MRI Findings:

  1. In MOG-ON, optic nerve inflammation often extends to the anterior part of the optic nerve (near the globe) and can involve the optic chiasm.
  2. AQP4-ON usually shows longer lesions that affect the optic nerve more posteriorly.

- Clinical Outcomes: MOG-ON generally has a better visual prognosis than AQP4-ON after relapses, with patients often recovering more vision.

Diagnosis

1. MOG Antibody Testing: The key diagnostic test is detecting MOG-IgG antibodies in the blood, usually through a cell-based assay. The presence of these antibodies confirms the diagnosis.

2. MRI of the Brain and Optic Nerves:

  1. Optic nerve inflammation (optic neuritis) can be seen, often involving the anterior part of the optic nerve.
  2. Brain MRI in MOGAD patients typically shows fewer and less extensive lesions than in multiple sclerosis (MS) or NMOSD.

3. Lumbar Puncture (CSF Analysis): Cerebrospinal fluid may show mild inflammation (increased white blood cells and protein), but unlike MS, oligoclonal bands are rarely seen in MOG-ON.

### Differentiation from Multiple Sclerosis (MS): - Unlike MS, MOG-ON usually does not show the classic brain lesions associated with MS. - MOG-ON tends to have more optic nerve involvement and is less likely to lead to the progressive disability commonly seen in MS.

The 2022 International Consensus Diagnostic Criteria for Optic Neuritis include optical coherence tomography (OCT). The diagnostic value of intereye difference (IED) metrics is high for ON in patients with multiple sclerosis and aquaporin-4 antibody seropositive neuromyelitis optica spectrum disorders, but unknown in Myelin oligodendrocyte glycoprotein antibody-associated optic neuritis(MOG-ON).

A multicenter validation study was conducted on the published IED cutoff values (>4% or >4 μm in the macular ganglion cell and inner plexiform layer [mGCIP] or >5% or >5 μm in the peripapillary retinal nerve fiber layer [pRNFL]) in individuals with MOG-ON and age-matched and sex-matched healthy controls (HCs). Structural data were acquired with Spectralis spectral-domain OCT >6 months after ON. Volpe et al. calculated sensitivity, specificity, and receiver operating characteristics for both intereye percentage (IEPD) and absolute difference (IEAD).

A total of 66 individuals were included (MOG-ON N = 33; HCs N = 33). ON was unilateral in 20 and bilateral in 13 subjects. In the pooled analysis, the mGCIP IEPD was the most sensitive (92%), followed by the mGCIP IEAD (88%) and pRNFL (84%). The same pattern was found for the specificity (mGCIP IEPD 82%, IEAD 82%; pRNFL IEPD 82%, IEAD 79%).In subgroup analyses, the diagnostic sensitivity was higher in subjects with unilateral ON (>99% for all metrics) compared with bilateral ON (61%-78%).

In individuals with MOG-ON, the diagnostic accuracy of OCT-based IED metrics for ON was high, especially for mGCIP IEPD.

Classification of evidence: This study provides Class III evidence that the intereye difference in OCT can distinguish between those with MOG and normal controls 1)

### Treatment: The goals of treatment are to manage acute episodes, prevent relapses, and reduce long-term disability.

1. Acute Attack Management:

  1. High-Dose Corticosteroids: The first-line treatment for an acute attack is intravenous methylprednisolone to reduce inflammation.
  2. Plasma Exchange (PLEX): In severe cases or if steroids are ineffective, plasma exchange may be used to remove antibodies from the blood.

2. Long-Term Immunosuppressive Therapy:

  1. Immunosuppressants: To prevent relapses, long-term immunosuppressive therapies may be necessary. These include:
    1. Rituximab: A monoclonal antibody that targets B-cells.
    2. Mycophenolate Mofetil or Azathioprine: Used to suppress the immune system and reduce the risk of relapses.
  2. Long-term therapy is often needed as relapses can occur after stopping treatment.

3. Symptom Management:

  1. Physical Therapy: For mobility and rehabilitation in cases where spinal cord involvement or weakness is present.
  2. Visual Rehabilitation: If vision loss persists after an acute episode.

### Prognosis: - Better Visual Recovery: Compared to NMOSD, MOG-ON tends to have a better visual prognosis following relapses. Most patients recover significant vision after acute attacks, but some residual deficits may remain. - Relapsing Course: MOG-ON is often relapsing, meaning multiple episodes of optic neuritis or other neurological symptoms can occur over time. Ongoing immunosuppressive therapy is typically needed to reduce the frequency and severity of relapses.

### Research and Advances: - Ongoing studies aim to better understand the role of MOG antibodies in demyelinating diseases and develop more targeted therapies that can specifically modulate the immune response in MOGAD, potentially leading to better patient outcomes with fewer side effects.

In summary, MOG-ON is a distinct form of optic neuritis associated with MOG antibodies, characterized by recurrent optic nerve inflammation and generally good visual recovery, but with a risk of relapses. Early diagnosis and appropriate long-term immunosuppressive therapy are critical for managing the condition and preventing further neurological damage.

1)
Volpe G, Jurkute N, Girafa G, Zimmermann HG, Motamedi S, Bereuter C, Pandit L, D'Cunha A, Yeaman MR, Smith TJ, Cook LJ, Brandt AU, Paul F, Petzold A, Oertel FC. Diagnostic Value of Inter-Eye Difference Metrics on OCT for Myelin Oligodendrocyte Glycoprotein Antibody-Associated Optic Neuritis. Neurol Neuroimmunol Neuroinflamm. 2024 Nov;11(6):e200291. doi: 10.1212/NXI.0000000000200291. Epub 2024 Sep 4. PMID: 39231384.
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