OCT – diagnosis and prognosis


ECTRIMS-ACTRIMS 2023 presented new data on the use of optical coherence tomography (OCT) as a biomarker in multiple sclerosis. The following is a brief summary of recent findings.

A multicentre group in Europe proposed that OCT abnormalities may be a useful alternative to oligoclonal banding to meet dissemination in time (DIT) criteria for a diagnosis of MS (Buenrostro et al. ECTRIMS-ACTRIMS 2023;P402). OCT data were obtained for the period 2011-2020 in 178 patients presenting with a first episode of demyelination. Over a mean four-year follow-up, 30% were diagnosed with MS. Predictors of MS conversion were lower peripapillary retinal nerve fiber layer (pRNFL) and ganglion cell and inner plexiform layer (GCIPL) thickness. Proposed cut-off values were pRNFL <98 µm and  GCIPL <68 µm. McDonald 2017 DIT criteria (OCB, MRI) were not predictive of MS conversion. The authors suggested that OCT markers would be a useful adjunct to conventional DIT measures.

A separate study examined how OCT might be used to differentiate MS from MOG antibody disease (MOGAD) (Pakeerathan et al. ECTRIMS-ACTRIMS 2023;P214). The retrospective study analysed data for 98 patients with optic neuritis (ON) diagnosed with MS or MOGAD. Bilateral ON was significantly more common in MOGAD vs. MS (46.7% vs. 11.8%). MOGAD was characterized by a global pattern of atrophy, while temporal atrophy was more common in RMS. pRNFL thinning was significantly more severe in MOGAD; high-contrast visual acuity was better preserved in MS. Bilateral ON and atrophy of non-temporal pRNFL quadrants differentiated MOGAD from MS (77.3% sensitivity, 80.3% specificity). The authors concluded that MOG IgG testing would be appropriate in patients with these findings.

A retrospective analysis of 69 PPMS patients found that pRNFL was correlated with greater brain atrophy (GM, WM, BPF) and lower spinal cord cross-sectional area (Bollo et al. ECTRIMS-ACTRIMS 2023;P631). A lower pRNFL thickness (<87μm) was associated with a higher proportion of patients with spinal cord lesions (>3 lesions: 89% vs. 68%) and lesions at the bulbomedullary junction (75% vs. 43%). pRNFL <87μm was the only measure that was predictive of disability progression (hazard ratio 3.44). At two years, 83% showed progression in the <87μm group vs. 25% in the >87μm group.

Similar findings were reported in a German multicentre study of 505 MS patients and controls (Kramer et al. ECTRIMS-ACTRIMS 2023;P213). GCIPL and inner nuclear layer thickness were predictive of progression in PPMS. However, there was substantial measurement variability, suggesting that longitudinal assessments in individual patients would not be useful.

Drug response
The Vienna group obtained a rebaselined OCT at 6-12 months after DMT initiation and after a median of 37 months of treatment in 291 RMS patients (Bsteh et al. ECTRIMS-ACTRIMS 2023;P624). There was no significant difference in the mean annualized rate of RNFL thinning among patients receiving dimethyl fumarate, teriflunomide, glatiramer acetate or beta-interferon. The annualized rate was somewhat less with S1P receptor modulators and cladribine. The rate of RNFL thinning was significantly lower in patients receiving natalizumab and anti-CD20 agents.

Novel approaches
The outer plexiform layer (OPL) has been less studied in MS research. MS-SMART investigators hypothesized that the OPL, which has a high microglia content, might be a useful indicator of slowly expanding lesions (SEL), which are characterized by chronic inflammation that is primarily driven by microglia (De Angelis et al. ECTRIMS-ACTRIMS 2023;P629). The study included 165 patients with SPMS. A thicker OPL at baseline was predictive of SEL volume; no other OCT measures were associated with SELs. The group also noted that SELs, but not OPL thickness, were predictive of brain volume change at 96 weeks.

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