Atypical forms of optic neuritis.

Inflammatory optic neuritis (ON) represents a frequent clinical situation in neurology and ophthalmology. The most current etiology is multiple sclerosis (MS) but, when MRI and Cerebrospinal fluid (CSF) analyses are normal, ON is usually considered as "idiopathic" with a suspected viral etiology. In rare cases, a systemic disease such as sarcoidosis, lupus or Sjögren syndrome may be diagnosed. In several cases either a recurrence or a myelitis may occur without any argument for MS. In the first case, it corresponds to relapsing inflammatory optic neuritis (RION) and in the second case to neuromyelitis optica (NMO). In the present paper, the author successively presents the various clinical situations and complementary findings (infectious, vasculitis, NMO or idiopathic) that can lead to a differential diagnosis of MS in a context of ON.