One of the main unsolved issues in the clinical management of neuromyelitis optica spectrum disorders (NMOSD) is the lack of biomarkers predicting short-term relapses. In physiological conditions, the blood brain barrier (BBB) protects the CNS from water unbalance, with aquaporin-4 (AQP4) water channels on astrocytes podocytes being the main regulator of water influx and efflux. In NMOSD, BBB integrity might be threatened by the presence of antibodies targeting AQP4 water channels and triggering complement-mediated astrocytes damage. In line with this, increased T2-signal in acute lesions (“bright spotty lesions”) is considered specific for NMOSD. However, it remains unexplored whether these patients present a chronic water unbalance.
To provide an indirect estimation of brain water content in NMOSD by measuring T2-relaxation time (T2rt) and to assess whether it differs in patients having a short-term relapse.
In this multicenter MR study, T2rt was calculated from brain dual echo turbo spin echo images assuming a mono exponential decay. T2rt maps of normal appearing white matter (NAWM), gray matter (GM) and basal ganglia were obtained from 77 AQP4-positive NMOSD and 84 HC. Short-term relapses were defined as those occurring within one month before or after MRI scan. Differences between NMOSD and HC were assessed with age-, sex- and site-adjusted linear models. ROC analyses were run to identify discriminators between stable and short-term relapsing patients.
NMOSD patients and HC had similar ages. Compared to HC, T2rt was increased in the GM (103 vs 97 ms), NAWM (88 vs 84 ms) and putamen (75 vs 72 ms) of NMOSD patients (p<0.001 for all). Short-term relapses occurred in 20/77 (26%) of patients. According to ROC analysis, T2rt cut-offs of 87 ms in the NAWM, 87 ms in the thalamus and 88 ms in the caudatus were able to discriminate between short-term relapsing and stable patients with good accuracy (AUC=0.70, 0.76 and 0.79 respectively, p≤ 0.027).
NMOSD patients had increased T2rt values, in line with the hypothesis of subclinical water accumulation in this disorder. The burden of T2rt alterations might be useful for identifying those patients with incipient or recent relapses.