Abstract: The present invention relates to a method of diagnosing primary progressive multiple sclerosis (PPMS) in a patient suspected of having PPMS. Further, the present invention relates to a method of determining the course of PPMS in a patient having PPMS. Furthermore, the present invention relates to a method of determining the severity of PPMS in a patient suspected of having PPMS. It also relates to the use of at least one metabolite for diagnosing PPMS in a patient suspected of having PPMS, for determining the course of PPMS in a patient having PPMS, or for determining the severity of PPMS in a patient suspected of having PPMS. In addition, it relates to a kit for diagnosing PPMS in a patient suspected of having PPMS, for determining the course of PPMS in a patient having PPMS, or for determining the severity of PPMS in a patient suspected of having PPMS.