Evaluation of optic nerve functions in subacute combined degeneration using visual evoked potential and diffusion...

Area of Science:

• Neuroscience
• Ophthalmology
• Radiology

Background:

• Subacute combined degeneration (SACD) is a neurological disorder often associated with vitamin B12 deficiency.
• Optic nerve involvement in SACD can be subtle and may not be detected by conventional imaging.
• Diffusion tensor imaging (DTI) and visual evoked potentials (VEP) offer sensitive methods to assess white matter integrity and function.

Purpose of the Study:

• To evaluate optic nerve involvement in SACD using DTI and VEP.
• To assess the impact of cobalamine treatment on DTI and VEP parameters in SACD patients.
• To correlate DTI findings with VEP abnormalities in the optic nerve.

Main Methods:

• Six SACD patients and six controls underwent visual acuity, visual field, color vision, and pattern shift VEP testing.
• Optic nerve MRI and DTI were performed, calculating fractional anisotropy ratio (FAR), axial diffusivity ratio (ADR), radial diffusivity ratio (RDR), and mean diffusivity ratio (MDR).
• Patients received hydroxyl cobalamine treatment, with repeat VEP and DTI studies at 3 months.

Main Results:

• While visual functions were normal, five SACD patients showed prolonged P100 latency on VEP.
• SACD patients exhibited reduced optic nerve FAR and increased MDR and RDR compared to controls.
• Reduced FAR correlated significantly with prolonged P100 latency (r = -0.88).

Conclusions:

• Optic nerve DTI reveals reduced fractional anisotropy (FA) values in SACD patients, correlating with prolonged P100 latency.
• Cobalamine treatment led to an increase in FAR and improvement in P100 latency, indicating myelin repair.
• DTI and VEP abnormalities suggest subclinical optic nerve myelin dysfunction in SACD, responsive to treatment.