Idiopathic Inflammatory Demyelinating Diseases (IIDDs), sometimes known as Borderline forms of multiple sclerosis^[1], is a collection of multiple sclerosis variants, sometimes considered different diseases^[2].

The list of these diseases depends of the author, but usually are included:

• Optic-spinal MS and neuromyelitis optica (NMO or Devic’s disease), which are currently considered variants of the same condition.
• Acute disseminated encephalomyelitis or ADEM, a closely related disorder in which a known virus or vaccine triggers autoimmunity against myelin.
• Balo concentric sclerosis, a pathological form.
• Schilder disease or diffuse myelinoclastic sclerosis: is an infrequent disease that presents clinically as a pseudotumoural demyelinating lesion; and is more common in children.^[3][4]
• Marburg multiple sclerosis, pathological form, also known as malignant, fulminant or acute MS.

As MS is an active field for research, the list is not closed or definitive. For example, some diseases like Susac’s syndrome (MS has an important vascular component ^[5]) or autoimmune variants of peripheral neuropathies like Guillain-Barré syndrome could be included.

Some authors also think that primary progressive multiple sclerosis should be considered a different entity from standard MS^{[6] [7]}. Others maintain the opposite^[8].

Finally, also a dual classification of these diseases has been proposed, according to the shape of edges of the scars, in MS-like and ADEM-like^[9]

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