Patients with neuromyelitis optica spectrum disorder (NMOSD) have abnormal enlargement and impaired water diffusion along the perivascular space, a new study published in the Annals of Neurology found. These features may correlate with disease severity and pathogenesis.

The perivascular space is outlined by astrocytes, which regulate fluids exchange via the aquaporin-4 water channel. In NMOSD, the immune system mistakenly attacks aquaporin-4. The authors of the present study hypothesized that the disease could therefore be associated with abnormalities in the perivascular space.

To test their hypothesis, they analyzed 34 patients with NMOSD and 46 healthy volunteers with standardized 3.0 Tesla magnetic resonance imaging (MRI) protocol including conventional and diffusion-tensor imaging. They evaluated macroscopic and microstructural abnormalities in the perivascular space in terms of enlargement and water diffusivity.


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Read more about the pathophysiology of NMOSD

The results showed that patients with NMOSD had a higher frequency of severe perivascular space enlargement in a region of the brain called the centrum semiovale. This correlated with deep grey matter atrophy and poorer cognition.

Patients with NMSOD also had reduced water diffusivity compared to healthy individuals. Lower water diffusivity, the volume of the deep grey matter, and the volume of the cortex could help differentiate between patients and healthy people, the authors suggested. Moreover, lower water diffusivity, number of myelitis, and a higher volume of T2-lesions were associated with worse disability.

They concluded that the automated diffusion along perivascular spaces index could help identify and monitor patients with NMOSD. “Future studies are warranted to better clarify the pathophysiological correlates of this finding and its clinical value,” they wrote.

The diagnostic process of NMOSD involves a physical examination and medical history followed by an eye examination, MRI to assess the optic nerve, blood tests, and in some cases, a lumbar puncture.

Reference

Cacciaguerra L, Carotenuto A, Pagani E, et al. MRI evaluation of perivascular space abnormalities in neuromyelitis optica. Ann Neurol. Published online May 20, 2022. doi:10.1002/ana.26419