Makindo Medical Notes

Optic Neuritis: A condition characterized by inflammation of the optic nerve, often presenting with colour desaturation (typically affecting red), visual loss, and sometimes pain with eye movement. The fundus appears normal in two-thirds of cases, while one-third show some degree of disc oedema.

About

• Optic Neuritis: Inflammation of the optic nerve leading to altered vision.
• Retrobulbar Neuritis: Inflammation affecting the optic nerve posterior to the optic disc, which is not visible on fundoscopy.

Aetiology

• Demyelinating Diseases: Multiple sclerosis (MS), neuromyelitis optica (NMO), acute disseminated encephalomyelitis (ADEM).
• Inflammatory Causes: Sarcoidosis, systemic lupus erythematosus (SLE), paraneoplastic syndromes, post-infectious causes, Behçet's disease.
• Infectious Causes: Syphilis, tuberculosis, Lyme disease, HIV, cytomegalovirus (CMV), herpes viruses.
• Ischaemic Causes: Anterior ischaemic optic neuropathy (AION), diabetic papillopathy, retinal artery or vein occlusion.
• Toxins: Methanol, arsenic, ethambutol, ciclosporin, tobacco, alcohol.
• Mitochondrial Causes: Leber hereditary optic neuropathy (LHON).
• Compression: Tumours, Paget's disease, thyroid eye disease.

Clinical Features

• Gradual loss or alteration of vision over hours to days.
• Pain or tenderness, especially with eye movements.
• Impaired direct pupillary response to light (relative afferent pupillary defect - RAPD).
• Reduced visual acuity, often with field defects such as scotomas.
• Long-term optic disc pallor due to nerve atrophy.
• Flashes of light (phosphenes) may be reported.

Differential Diagnoses

• Ischaemic optic neuropathy.
• Compression of the optic nerve (e.g., tumours, thyroid eye disease).
• Central retinal artery or vein occlusion.
• Leber hereditary optic neuropathy (LHON).
• Other inflammatory or autoimmune optic neuropathies.

Investigations

• Laboratory Tests:
  • Full blood count (FBC).
  • Antinuclear antibodies (ANA), angiotensin-converting enzyme (ACE), erythrocyte sedimentation rate (ESR).
  • Serology for syphilis and HIV.
• Imaging:
  • MRI of the brain and cervical spine to look for demyelinating plaques or other abnormalities.
• Specialist Tests:
  • Check for NMO IgG (neuromyelitis optica antibody).

Management

• Consult neurology or ophthalmology for suspected optic neuritis.
• Consider intravenous methylprednisolone for acute cases, particularly in the context of suspected demyelination.
• Treat underlying causes based on identified aetiology (e.g., antimicrobials for infections, immunosuppression for autoimmune causes).
• Monitor for progression to multiple sclerosis or other systemic conditions in demyelinating cases.