Pathogenic distinction between PP and SPMS still debated
Demyelination and Neurodegeneration along the Visual Pathway are more prominent in Secondary Progressive than Primary Progressive Multiple Sclerosis.
Objective: We aimed at using visual evoked potentials-VEPs and optical coherence tomography-OCT to compare the extent of demyelination and neurodegeneration in the visual pathway of primary progressive-PP and secondary progressive-SP MS patients.
Background: The pathophysiologic distinction between PP and SPMS is still debated.
Design/Methods: One hundred progressive MS patients (55 SP: disease duration-DD 20.1±7.6 years, median EDSS 6.0; 45 PP: DD 8.4±4.7 years, median EDSS 6.0) and 42 healthy controls-HC underwent testing with high-contrast visual acuity-VA, low contrast letter acuity-LCLA, full-field pattern-reversal VEPs and peripapillary RNFL measurement with OCT.
Results: After excluding eyes with previous optic neuritis-ON (unilateral in 18 SP and 2 PP, bilateral in 7 SP), VA did not significantly differ between SP and PP (HCVA 0.88±0.2 vs 0.94±0.2 decimal, p=0.424) and was significantly reduced than in HC (1.03±0.2, p<0.001 for SP and p=0.035 for PP). SP had significantly lower LCLA (0.19±0.1) vs PP (0.29±0.2, p=0.015) and vs HC (0.31±0.1, p<0.001). Mean binocular RNFL was significantly thinner in SP (81.1±12.03 μm) vs PP (88.7±9.9 μm, p=0.002), and in both subgroups vs HC (96.9±5.7 μm, p<0.001). RNFL was abnormally reduced in 58.9% (46/78) SP eyes vs 26.1% (23/88) PP eyes (p<0.001). VEPs were significantly delayed in SP (145.0±19.3 msec) vs PP (132.9±19.3 msec, p=0.003), and in both vs HC (116.2±5.2 msec, p<0.001). VEPs were abnormal in 76.9% (60/78) SP eyes vs 61.3% (54/88) PP eyes (p=0.020).
Conclusions: Despite similar global disability, SP patients have greater visual impairment, demyelination and neurodegeneration along the visual pathway compared with PP. These aspects may reflect distinct pathophysiologic processes between the two courses of the disease.