Optical Coherence Tomography Angiography Helps Differentiate MS and NMOSD

Disease Spotlight | <b>Disease Spotlight: NMOSD</b>

Although existing research has shown structural differences between multiple sclerosis and neuromyelitis optica spectrum disorder in following optic neuritis, the new report also covers non–optic neuritis eyes.

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A study published in Scientific Reports revealed that optical coherence tomography angiography (OCTA) can help physicians better distinguish between multiple sclerosis (MS) and neuromyelitis optica spectrum disorder (NMOSD).

The data explains that NMOSD and MS are autoimmune demyelinating diseases and both sometimes present with optic neuritis (ON). Following optic neuritis, studies have shown that the use of spectral-domain optical coherence tomography (SD-OCT) to measure ganglion cell complex (GCC) and retinal nerve fiber layer (RNFL) thickness can help distinguish between the two, because the eyes of patients with NMOSD had greater reductions in GCC and RNFL thickness than MS eyes after ON.

Senior author Marcin Stopa, MD, PhD, Department of Ophthalmology, Poznan University of Medical Sciences, and colleagues wrote, "However, a similar OCTA study of the non-ON eyes has not been reported so far." They hypothesized that a comparative analysis of OCT measurements could "indicate the characteristic pattern of lesions in ON and non-ON eyes differentiating these diseases." They also posited that disease-specific intra-eye changes might allow for differentiation.

People with MS and NMOSD who were patients at Poznan University’s Ophthalmology and Neurology departments between June 2018 and September 2020 were recuited for the study. Thirteen patients with NMOSD and 40 patients with MS were evaluated using SD-OCT and OCTA.

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Patients’ medical histories, including history of ON, were obtained and integrated into the data. All 40 patients with MS were on a disease-modifying therapy, the most common of which was fingolimod (Gilenya). Only 6 patients with NMOSD were being treated; 5 received azathioprine and 1 received intermittent intravenous immunoglobulin.

Using SD-OCT and OCTA, the investigators found a number of differences and similarities based on the patient’s disease. For instance, in ON eyes, radial peripapillary capillary vessel density was significantly decreased in the superior (S) and inferior (I) sectors in patients with NMOSD compared with patients with MS. In non-ON eyes, however, the MS group was distinguished by a reduced temporal sector.

Furthermore, ON eyes had thinner RNFL layers in the I and temporal (T) quadrants when they had NMOSD compared with MS.

Other areas, including the macular capillary plexuses and GCC thickness, were not distinguishable between NMOSD and MS on ON and non-ON eyes.

The authors said comparing measurements provided the clearest diagnostic tool. "The ratios, based on the disease-specific intra-eye RPC vessel density reduction pattern, were the best discriminants between NMOSD and MS (ie, inferior to nasal [I/N] and I/T ratios for ON eyes, and S/T and N/T ratios for non-ON eyes,” they wrote.

Their study was subject to some limitations, they noted, such as the small sample size of patients with NMOSD, which they attributed to the low prevalence of the disease. The study was also a single-center study, and thus did not evaluate a diverse population.

Still, the investigators said their data show that a distinct pattern of RPC vessel density could help differentiate between NMOSD and MS and the use of OCTA-based ratios could help improve diagnostic accuracy.