At the baseline visit, blood samples to assess biomarkers (glutamate, calcitonin gene-related peptide, glial fibrillary acidic protein and S100β) will be taken. Patients will then be randomised (in a 1:1 ratio) to commence either ibudilast or placebo treatment, which will continue for 8 weeks. Subsequently participants will undergo a 4-week washout period. At the end of the washout period a second 8-week treatment block with the alternative treatment will commence.