This patient presented with unilateral visual loss. This T2-weighted fat-saturated coronal image shows high signal in the left optic nerve, consistent with optic neuritis (click image for arrow). The patient tested positive for p-ANCA (perinuclear antineutrophil cytoplasmic antibodies), raising the possibility of systemic vasculitis and a differential diagnosis of ischaemic optic neuropathy.
Optic neuritis clinically presents with visual loss and pain. It is most commonly a demyelinating disorder, and there is a strong association with multiple sclerosis, with 38% of patients presenting with isolated optic neuritis developing MS in the following 10 years. Other associations include Devic’s disease (optic neuritis and myelopathy, distinct from MS). Other causes of optic neuritis include: infections (TB, viruses); radiotherapy; drug reactions; and vasculitis. Optic neuritis often resolves spontaneously, although many are left with mild visual impairment. Recurrence occurs in 35% within 10 years and may be ipsi- or contralateral.
MR imaging serves to confirm the clinical diagnosis, and assess the brain for evidence of demyelination. The affected optic nerve is of high signal on T2W images, with minimal expansion. There is frequently mild contrast enhancement. One or more white matter lesions seen in the brain correlates with a 56% risk of developing clinical MS within 10 years. With no white matter lesions seen, this risk is 22%. MRI findings are useful to guide therapy, including the early use of interferon β.
P-ANCA-associated retinal vasculitis has been described, however as up to 5% of the normal population are p-ANCA positive, the meaning of the finding in this patient is unclear. Cerebral catheter angiography is being considered to find evidence of vasculitis.
Credit: Dr Laughlin Dawes