In multiple sclerosis (MS), thalamic integrity is affected both directly by demyelination, neuronal loss and increasing iron concentration, and indirectly by remote gray and white matter lesions affecting neural projections into and out of the thalamus. Thalamic atrophy may therefore reflect a large fraction of MS-related brain damage and thus represent a useful marker of overall damage and therapeutic efficacy.
To assess the efficacy of ocrelizumab (OCR) in patients switching to or maintaining OCR therapy on thalamic atrophy in patients with relapsing MS (RMS) and primary progressive MS (PPMS), participating in the OPERA I/II (NCT01247324/NCT01412333) and ORATORIO (NCT01194570) Phase III trials, respectively.
At the end of the double-blind controlled treatment period in OPERA I/II, patients entered the open‑label extension (OLE), and either continued to receive OCR (OCR-OCR) or switched from interferon β-1a (IFN β-1a) to OCR (IFN β-1a-OCR). In ORATORIO, patients entered the OLE ~3–9 months after the double-blind period cut-off and either continued OCR (OCR-OCR) or switched from placebo (PBO) to OCR (PBO-OCR). Changes in thalamic volume from the core trial baseline were computed using Jacobian integration and analyzed using a mixed-effect repeated measurement model, adjusted for baseline volume, age, baseline gadolinium-enhancing lesions (presence/absence), baseline T2 lesion volume, region (US vs rest of the world), Expanded Disability Status Scale category (<4, ≥4), week, treatment, treatment and time interaction, and treatment and baseline volume interaction.
In the OLE of OPERA I/II, changes (%) in thalamic volume from baseline at OLE Week 46, 94, 142, 190, and 238, were: –2.88/–2.12 (p<0.001), –3.31/–2.36 (p<0.001), –3.61/–2.78 (p<0.001), –3.68/–3.03 (p<0.001), and –4.07/–3.41 (p<0.001), for IFN β-1a-OCR/OCR-OCR patients, respectively. During the OLE of ORATORIO, changes in thalamic volume at OLE Day 1, Week 48, 96, and 144, were: –3.46/–2.44 (p<0.001), –3.93/–2.61 (p<0.001), –4.30/–3.25 (p<0.001), and –4.86/–3.62 (p<0.001), for PBO-OCR/OCR-OCR patients, respectively.
In the OLE, patients with RMS and PPMS who were initially randomized to ocrelizumab experienced less thalamic volume loss compared with those initiating ocrelizumab later.