A method of determining in vitro the presence of a multiple sclerosis

The invention relates to a method of in vitro determination of the presence of primitively progressive multiple sclerosis in a subject, comprising the detection of IL-29 and/or of the IL-28Ra receptor in a biological sample to be tested arising from said subject and the comparison of the level detected with that of a reference sample. It also relates to the in vitro or ex vivo use of one or more compound(s) capable of detecting specifically IL-29 and/or the IL-28Ra receptor so as to determine the presence of primitively progressive MS, as well as kits comprising such compound(s).