Value of Annual MRI Monitoring in Patients With Multiple Sclerosis Treated With Ocrelizumab: A Number Needed to Scan...

Current guidelines recommend annual MRI scans during treatment with disease-modifying therapies, including ocrelizumab, in patients with multiple sclerosis (MS) to monitor treatment effectiveness and safety. However, the low rate of radiologic disease activity during long-term ocrelizumab treatment suggests that this recommendation should be re-evaluated to reduce burden on ocrelizumab-treated patients and the healthcare system. We aimed to describe the frequency of radiologic follow-up and the occurrence of radiologic disease activity in a cohort of ocrelizumab-treated MS patients to provide insight into the clinical value and efficiency of annual MRI monitoring in routine practice.

We included ocrelizumab-treated MS patients from the Amsterdam MS Cohort, who had at least 2 brain MRI scans performed during ≥3 months of treatment. MRI scans were performed as part of routine clinical care and clinical MRI reports issued by radiologist were used. Radiologic activity was defined as either ≥1 contrast-enhancing lesions on a MRI scan performed ≥3 months after ocrelizumab initiation or any new/enlarging T2 lesions on a subsequent MRI scan compared with a scan performed at least ≥3 months after ocrelizumab initiation. The number needed to scan (NNS) was calculated as the inverse of the predicted probability of radiologic disease activity as a function of treatment duration in months, estimated using a mixed-effects logistic regression model.

A total of 342 patients (mean age at start ocrelizumab 40.3 years (SD 10.8); 65.8% female; 208 relapsing-onset MS and 41 primary progressive MS) were included, contributing 1,639 follow-up MRI scans. Radiologic disease activity was detected in 29 scans in 23 patients (1.8% of scans; 6.7% of patients) over a median treatment duration of 49 months. The NNS increased with treatment duration, especially after 24 months of treatment, reaching 81.3 at month 30 and 152.9 at month 36.

Routine annual MRI monitoring in patients with asymptomatic ocrelizumab-treated MS never led to treatments changes. The increasing NNS over time, especially after 2 years of treatment, indicates that MRI intervals can be safely extended in patients with stable MS treated with ocrelizumab, potentially doubling the interval from treatment year 2 onward (i.e.,; rebaseline, year 1, year 2, year 4, and year 8, etc.).