he good news is that there are two well-designed PPMS trials recruiting patients at present: the first and most advanced is the Fingolimod (Novartis) study and the Ocrelizumab (anti-CD20, Roche) is about to start. The latter study is based on the observations from a subgroup analysis of the Rituximab PPMS trial that showed younger patients (<51 years) and those with active MRI scans (Gd-enhancing lesions) responded to treatment; i.e. had a slower rate of disease progression. Please see Hawker et al. Ann Neurol. 2009 Oct;66(4):460-71.
Unfortunately there are no DMTs that have been shown to work in PPMS. The reasons for this are complex and related to many factors; (1) firstly our poor understanding of the mechanisms underlying non-relapsing progressive MS; (2) the assumption that PPMS is not that inflammatory (in my opinion an incorrect assumption); (3) poor application of diagnostic criteria for PPMS* and (4) poor trial design (the EDSS is simply not up to the task of measuring disease progression over a short period of time).
* The original McDonald diagnostic criteria required patients to have an abnormal spinal fluid analysis. However the revisions of these criteria have not made this an absolute requirement, which has altered the natural history of PPMS. Patients with normal CSF analysis do better than those with a negative CSF.