Question 4: What is the likely diagnosis?

Question 4: What is the likely diagnosis?

Answer

This patient most likely has non-arteritic anterior ischaemic optic neuropathy. However, as this is a diagnosis of exclusion, other conditions need to be ruled out first. The differential diagnosis includes

• Other optic neuropathies, including anterior optic neuritis (idiopathic, demyelinating, sarcoid-related, etc)
• Anterior compressive optic neuropathy (from anterior orbital lesions)
• Infiltrative optic neuropathy
• Advanced glaucoma

Relevant blood tests and neuroimaging should be arranged to exclude the other differential diagnoses.

Non-arteritic anterior ischaemic optic neuropathy (NAION) is the most common acute optic neuropathy in patients over 50 years of age, with an estimated annual incidence in the United States of 2.3-10.3 per 100,000 population. The disease affects Caucasians more than African-American or Hispanics.

Patients typically present with persistent sudden, painless, unilateral loss of vision and visual field defects. Visual acuity in patients with NAION varies considerably from 6/6 to no perception of light.

Clinical features of NAION include relative afferent pupillary defect (RAPD), diffuse or segmental optic disc swelling in the affected eye, which may be associated with flame peripapillary haemorrhages; and a contralateral crowded ‘disc at risk’. Soft exudates are unusual. The swelling typically resolves within 4-6 weeks and is replaced by sectoral or diffuse pallor, as seen in our patient.

An important differential includes arteritic anterior ischaemic optic neuropathy (AAION), caused by occult giant cell arteritis (GCA). As such, an urgent full blood count, ESR and CRP should be requested to rule out GCA. Occult GCA manifests as acute blindness with minimal systemic symptoms. In both conditions, the optic nerve head is swollen with flame-shaped haemorrhages, however only AAION is associated with pallor of the swollen nerve (due to severe infarction). AAION is more likely to be present in the older population.

Answer ends