Eye scans may be helpful tool to distinguish NMOSD, MS in patients
Study finds noninvasive technique could differentiate the 2 conditions
Using noninvasive eye scans may help clinicians to determine if patients — particularly those in early disease stages — have neuromyelitis optica spectrum disorder (NMOSD) or multiple sclerosis (MS), both immune system disorders.
That’s according to a review of published studies that together reveal that people with NMOSD have a lower density of blood vessels in the retina, the light-sensitive tissue at the back of the eye, than individuals with MS.
The researchers detected these differences using optical coherence tomography angiography, known as OCT-A, a noninvasive eye scan technique that directly visualizes blood vessels in the retina.
“These preliminary findings highlight that OCT-A may hold promise as a diagnostic tool for differentiating MS and NMOSD,” the researchers wrote.
The study, “Optical coherence tomography angiography biomarkers in multiple sclerosis and neuromyelitis optica spectrum disorders: a systematic review,” was published in the International Journal of Retina and Vitreous.
NMOSD and MS are two related but distinct neurodegenerative conditions marked by inflammatory attacks on certain parts of the brain and spinal cord. These abnormal attacks result in damage and loss of myelin, the protective sheath that surrounds nerve fibers.
Similarities between MS, NMOSD make them hard to distinguish
Due to their similarities, it can be challenging to differentiate NMOSD from MS, particularly in the early stages of the disease. Specifically, inflammation of the optic nerve, known as optic neuritis, and the spinal cord, which is called myelitis, can appear in both conditions. However, optic neuritis is severe in NMOSD, unlike in MS.
In current practice, an NMOSD diagnosis primarily relies on the detection of self-reactive antibodies against the water channel protein aquaporin-4 (AQP4), which is present in nerve-supporting cells. Still, about 25% of NMOSD patients test negative for these antibodies, the researchers noted.
Here, a research team from Iran and the U.S. sought to determine if OCT-A — a noninvasive imaging technique that utilizes light waves to visualize blood vessels in the retina — could distinguish between MS and NMOSD. To that end, the team conducted a review of published studies.
“Imaging markers are necessary to differentiate between these disorders, especially when [blood] testing is unavailable or unclear,” the team wrote.
Following a database search, the researchers selected nine studies involving 181 people with MS and 166 with NMOSD. Four studies were conducted in Poland, two in China, and one each in Germany, Korea, and Turkey. A majority of the patients — 71% with MS and 87% with NMOSD — were women, and nearly all NMOSD patients (89%) tested positive for anti-AQP4 antibodies.
According to a study that enrolled MS and anti-AQP4-positive NMOSD patients, those with NMOSD had a significantly lower density of blood vessels in the retina, particularly in the macula — the functional center of the retina — compared with MS patients.
In studies involving patients with optic neuritis, significantly lower blood vessel densities were observed in several areas of the retina in the eyes of NMOSD patients relative to those with MS.
Researchers say eye scans known as OCT-A might aid in diagnosis
In addition to the macula, retinal regions affected in NMOSD with optic neuritis were the radial peripapillary capillaries (RPC) and the superficial radial capillary plexus, two distinct vascular networks within the retina. The peripapillary area, which surrounds the point where the optic nerve enters the eye at the back of the retina, was also more affected in NMOSD, even among those who tested negative for anti-AQP4 antibodies, the data showed.
In those without optic neuritis, MS patients had significantly lower RPC vessel density on the outer (temporal) side of the retina compared with individuals with NMOSD.
NMOSD with or without optic neuritis was also associated with a smaller foveal avascular zone (FAZ), a capillary-free area in the center of the fovea, a region of the retina responsible for sharp vision.
“The difference in FAZ size between NMOSD and MS eyes may be due to greater or persistent foveal inflammation in NMOSD, reflecting active disease, unlike MS, where inflammation is considered more self-limiting over time,” the researchers wrote.
This review identified differences in [optical coherence tomography angiography (OCT-A)] indices between [MS] and [NMOSD patients]. … These preliminary findings suggested that OCTA may provide complementary information to existing clinical, radiological, and serological [blood] tools.
Importantly, according to the team, there were no differences in vascular density in the peripapillary and macular areas in eyes without a history of optic neuritis in both MS and NMOSD patients.
That “[indicates] that [optic neuritis] may be a key factor in differentiating these disorders using OCT-A,” the team wrote.
One small study found no vascular differences between the optic neuritis eyes of the two patient groups, but a smaller FAZ was observed in the NMOSD patients.
“This review identified differences in OCT-A indices between [MS] and [NMOSD patients], with [people with] NMOSD exhibiting lower vessel densities in the peripapillary and macular regions and smaller FAZ areas compared to [individuals with] MS,” the team concluded. “These preliminary findings suggested that OCTA may provide complementary information to existing clinical, radiological, and serological tools.”
Still, the team researchers noted that further study is needed to “determine the diagnostic and prognostic relevance of OCTA metrics in clinical practice.”
About the Author
