Chronic relapsing inflammatory optic neuropathy

Chronic relapsing inflammatory optic neuropathy (CRION) describes a rare, recurrent, corticosteroid-responsive optic neuropathy that should be considered as an important differential diagnosis in patients with multiple episodes of suspected optic neuritis.

Epidemiology

The exact incidence of CRION is unknown. Generally, patients are young female adults, with one study finding a median affected age of approximately 35 years ¹.

Clinical presentation

CRION is characterised by subacute objective visual loss and pain with at least one relapse ^1-3. Papilloedema may also be present, but is not a cardinal clinical feature ^1,2. Relapses can occur in the same eye (more common) or in both eyes sequentially or simultaneously ^1-3.

Markers

Patients with CRIONAffected patients are generally negative for any blood biomarker, including NMO-IgG, and thus, CRION is generally a diagnosis of exclusion ^1,3. HoweverNotably, the relationship, if any, between CRION and MOG antibodies is not well established, with some authors claiming that many patients with CRION may be MOG antibody positive and may actually have recurrent or bilateral optic neuritis of anti-MOG associated encephalomyelitis instead ⁴.

Pathology

The underlying pathophysiology of CRION is unknown (as of September 2018), however it is thought to be immune-mediated due to the positive response patients have to immunosuppressant therapy ¹.

Radiographic features

Plain radiograph and CT are often unremarkable ¹, however, MRI is useful in the diagnosis of CRION.

MRI

Dedicated orbital views are ideal, demonstrating a thickened optic nerve with signal characteristics similar to thatthose seen in optic neuritis ^1-3:

• T2/FLAIR: high signal, more prominent with fat suppression
• T1 C+ (Gd): enhancement, more prominent with fat suppression

Unlike patients with demyelinating optic neuritis, such as in multiple sclerosis, accompanying parenchymal signal changes are usually absent, and have only been rarely reported in the literature ^1,3.

Treatment and prognosis

Acute management generally involves pulsed methylprednisolone, followed by a tapering regimen of oral prednisolone ¹. In the long term and once clinically stable, steroid-sparing immunosuppressants may be employed, such as azathioprine or cyclophosphamide ¹.

History and etymology

The condition was first described in a case series published by Desmond Kidd, an English neuro-ophthalmologist, and his colleagues in 2003 ².

Differential diagnosis

• clinically isolated syndrome of multiple sclerosis
• neuromyelitis optica spectrum disorder
• anti-MOG associated encephalomyelitis
• neurosarcoidosis
• ischaemic optic neuropathies
• infectious optic neuropathies (e.g. neurosyphilis)
• metabolic optic neuropathies (e.g. methanol poisoning)
• Leber hereditary optic neuropathy