Background: 80-100% of patients with multiple sclerosis (MS) display a polyspecific, intrathecal humoral immune response against a broad panel of viral agents including antibodies to measles, rubella and varicella zoster virus as its three most abundant components (called MRZ reaction [MRZR]). However, a positive MRZR reaction can also be found in some patients with CNS vasculitis, another rare autoimmune condition, raising the question whether this marker is really of high specificity for MS as previously claimed or whether it just represents a non-specific marker of CNS autoimmunity. Besides MS and CNS vasculitis, paraneoplastic neurological disorders (PND) represent the best recognized models of CNS autoimmunity.
Objective: To investigate MRZR for the first time in patients with PND.
Patients and methods: Forty-two patients with MS and 34 with PND were compared in this study. The intrathecal synthesis of antibodies against measles, rubella, and varicella zoster virus was detected by calculation of the respective antibody indices (AI).
Results: A positive MRZ reaction as defined by a combination of at least two positive AIs was present in 37/42 patients with MS, but in none of the patients with PND (p < 0.0001). Median AI values differed significantly between groups (p < 0.0005).
Conclusions: Our results confirm that MRZR is not a general marker of CNS autoimmunity. Taking into account the very rarity of CNS vasculitis as well the lack of MRZR positivity in infectious inflammatory CNS conditions as previously demonstrated, MRZR might indeed be a promising marker of MS. Further investigations on MRZR in more rare autoimmune conditions, which were not available for analysis in this study, are now warranted to refine further the specificity of this parameter.