The thickness of two layers of nerve cells forming the back of the eye, or retina, can be used to distinguish patients with progressing forms of multiple sclerosis (MS) from those with stable disease, a study suggests.
In MS, previous studies have shown that shrinkage of the peripapillary retinal nerve fiber layer (pRNFL) — one of the layers of the retina that contains the nerve endings (axons) of neurons found in the retina — is an indicator of axonal degeneration that is linked to physical and cognitive disability progression.
But some studies are now suggesting that assessing changes in the thickness of the macular ganglion cell-inner plexiform layer (mGCIPL) — a combination of two retina layers that contain the cell bodies of neurons found in the retina — may be better to monitor MS progression.
“However, cut-off values regarding mGCIPL atrophy [shrinkage] for both cross-sectional and longitudinal use in individual patients are lacking,” researchers wrote.
To define the optimal cutoff values of mGCIPL thinning that could be used to distinguish patients with progressive MS from those with stable disease, investigators in Austria measured the thickness of the mGCIPL in 183 patients with relapsing MS over the course of three years.
Thickness measurements were performed using optical coherence tomography (OCT), a non-invasive imaging test that uses light to take pictures of the retina.
The team also compared the accuracy of the new cutoff values for mGCIPL to identify patients with progressive MS to those previously established for pRNFL.
From the 183 patients who were recruited to participate in the study, 168 completed it and were included in the final analyses. Of these, 64 patients (35%) were defined as clinically progressing during the observation period.
At the start of the study, the average thickness of the mGCIPL was lower in patients with disability progression, compared to those without disability progression — 77.3 versus 84.3 micrometers (mcm) in those without disability progression.
Statistical analyses indicated that patients whose mGCIPL measured less than 77 mcm in thickness had a 2.7 times higher risk of experiencing disability progression.
Using a cutoff value of 77 mcm for mGCIPL, and a previously established cutoff value of 88 mcm for pRNFL, researchers were able to correctly distinguish patients with progressive disease from those with stable MS in 66.7% (based on mGCIPL) and 63.1% (based on pRNFL) of the cases.
In the overall population of patients participating in the study, the mean annual loss of mGCIPL was 1 mcm. This value was higher among patients with progressive MS (2.1 mcm) and much lower among those with stable disease (0.3 mcm).
Statistical analyses also found that patients whose mean annual loss of mGCIPL was equal or greater than 1 mcm had an 18 times higher risk of having a clinical progressive form of MS.
At a cutoff value of 1 mcm for annual loss of mGCIPL, and a cutoff value of 1.5 mcm for pRNFL, mGCIPL showed superior sensitivity (87% versus 75% with pRNFL) at identifying patients with progressive disease.
Additional analyses also showed that values of annual loss of GCIPL were associated more strongly with clinical progression, disability progression, and cognitive decline than pRNFL loss values.
“In clinical practice, we advocate that regular — ideally annual — OCT measuring both mGCIPL and pRNFL should be included in routine disease monitoring, where sufficient quality of imaging and layer segmentation is available,” the team added.
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