Many causes exist for an ON, only the inflammatory ON will be discussed in this chapter.
The main cause is Multiple Sclerosis (MS) as 30% of optic neuritis occurs in the French cohort Kidsep.
It can also be an inaugural symptom of neuromyelitis optica syndrome or Devic syndrome, which includes ON and transverse acute myelitis associated with anti AQP4 antibodies.
Some viruses have also been implicated in the occurrence of this pathology, such as measles, varicella, mumps, herpes, Epstein-Barr virus (infectious mononucleosis), HIV, cytomegalovirus …
In rare cases, systemic diseases (such as sarcoidosis, lupus…) have also been implicated. Recently, causes of a relapsing optic neuritis have been described associated with anti-MOG antibodies.
Finally, there are isolated forms without any precise cause called idiopathic ON.

It is manifested by a sudden decrease in visual acuity with or without pain on eye movement. Older children can sometimes complain about loss of color vision.
The ocular damage is predominantly unilateral in the context of MS, whereas it is mostly bilateral when isolated or associated with Devic syndrome.

A thorough ophthalmologic examination is necessary to make the diagnosis.
The fundus examination may show a “papillitis”, an edema of the papilla that corresponds to the termination of the optic nerve. But it can sometimes be normal or show a papillary “palor”, which could be a late sign of a NORB.
Visual field is a key examination which, when feasible in children, can reinforce the diagnosis by highlighting a central, centro-cæcal or arcuate scotoma.
In order to search for arguments for an MS and thus to better monitor the child, additional explorations are carried out during the ON:

• A lumbar puncture : presence of> 10 cells was observed in 25% of the children followed in our cohort as well as an increase of proteins> 0.5 g /dl in 9%. It can specifically exclude infectious diseases as described above.
• Cerebral MRI is another key examination to detect lesions of optic nerves with contrast enhancement, but also lesions of the brain that could lead to MS diagnosis.
• Anti-AQP4 antibodies for the diagnosis of NMOSD diagnosis.
• Anti-MOG antibodies for the diagnosis of anti-MOG relapsing ON.

In the Kidsep cohort, 35% of children with a first attack of demyelination progressed to MS. This risk is even more important when there are central nervous system lesions outside of the optic nerves (42%).

The treatment consists on intravenous injections of high doses of methylprednisolone for 3 to 5 days depending on the symptoms and on the tolerance of the treatment.