Pattern II and pattern III MS are entities distinct from pattern I MS: evidence from cerebrospinal fluid analysis

Histopathological studies have demonstrated at least three different lesion patterns in early disease stages from patients diagnosed with multiple sclerosis (MS), termed patterns I, II and III [1, 2]. Pattern I lesions show T cell and macrophage infiltration. Pattern II is defined by additional antibody and complement deposition, suggesting a contribution of humoral mechanisms to disease pathology. Pattern III is characterized by distal oligodendrogliopathy with dysregulated myelin protein expression and oligodendrocyte apoptosis, but still occurs on an inflammatory background. A fourth pattern, defined by oligodendrocyte degeneration in the periplaque white matter, has been described in few autopsy cases of primary-progressive MS, but is rare. These findings raise the possibility that MS, a diagnosis currently based mainly on phenotypical, namely clinical and radiological features [3], may in fact be a pathologically heterogeneous syndrome rather than a single disease entity. Importantly, two recent studies demonstrated intraindividual homogeneity and persistence of pattern I, II and III lesions over time [4, 5], further corroborating the notion that lesion pathology may rather define pathogenetically distinct entities than reflect stage-dependent processes in the development of lesions.

Intrathecal IgG synthesis, as detected qualitatively by isoelectric focusing (IEF) of cerebrospinal fluid (CSF) and serum or quantitatively by calculation of the immunoglobulin CSF/serum ratio (QIgG), is present in 90–98% of MS patients, usually remains detectable over the entire course of disease and is considered a diagnostic mainstay in MS [6‐9].

In this study, we retrospectively compared the CSF profiles of patients who underwent brain biopsy as part of their diagnostic work-up and who could be unequivocally classified as having pattern I, pattern II or pattern III lesions, respectively.

In this study, we systematically analysed the results from 68 lumbar punctures in patients who were histopathologically diagnosed with pattern I, pattern II or pattern III MS according to previously published criteria [2]. The most striking finding was the lack of intrathecal IgG synthesis in the vast majority of samples from pattern II or pattern III MS patients. Intrathecal IgG synthesis is considered a diagnostic mainstay of MS. While previous studies reported a frequency of OCB in MS of 90–98% in European patients, 73% of samples from pattern II or pattern III MS patients, including all pattern III patients, were negative in the present European cohort. Moreover, OCBs were positive only transiently in the only two patients with non-pattern I lesions and follow-up data. Transient OCBs have been reported in other neuroinflammatory diseases such as neuromyelitis optica (NMO), acute disseminated encephalomyelitis or CNS infection, whereas OCBs are thought to persist over the entire disease course of MS [24, 25]. Similarly, the polyspecific, intrathecal antiviral IgG response as defined by at least two elevated CSF/serum antibody indices to measles, rubella and/or (so-called MRZ reaction) varicella zoster virus, which is seen in around 70% of patients with MS (and considered to represent non-specific bystander B-cell activation) [10‐14, 23], was missing in all patients with pattern II or III lesions tested. Some 91% of the pattern II and III MS samples did not even show a monospecific IgG response to one of the constituents of the MRZR; in contrast, a reaction to at least one of the three viral agents has been found in 89–94% of MS patients [14, 19]. Together, this strongly suggests that patients with pattern II and pattern III lesions are immunopathophysiologically distinct from patients with ‘pattern I MS’ as well as from previous MS cohorts [8, 10, 19].

This notion is further supported by the finding of additional, significant differences in CSF profiles between patients with pattern I lesions and patients with pattern II or III lesions. The latter group significantly more frequently had signs of compromised blood–CSF barrier function, had significantly higher CSF albumin concentrations and significantly higher and more frequently elevated CSF total protein levels (Tables 6 and 9; Fig. 3). In addition, an albuminocytological dissociation was more commonly seen in patients with type II or III lesions.

Although intraindividual persistence of a single lesion type over time has been shown in a larger cohort of biopsied patients [4, 5], there is an ongoing discussion on whether the various histopathological lesion patterns identified in MS really represent different entities or rather different stages of the same disease. Given that OCBs are a constant feature in MS, which once acquired does not normally vanish [24, 25] (except in rare patients treated with natalizumab [26, 27], a drug not used in any of our patients), the lack of OCB positivity or persistence in most pattern II and III patients provides particularly strong evidence in favour of the former hypothesis.

The term ‘multiple sclerosis’ refers to a clinicoradiologically defined syndrome. There is currently no proof that all patients presenting with acute CNS demyelination and dissemination in time and space share the same underlying pathogenesis. Instead, several lines of evidence suggest that the current ‘phenotypic’ definition of MS may cover more than one disease: (i) pathological studies have demonstrated histopathological heterogeneity among patients with MS [1, 4, 5]; (ii) clinical studies have shown differences in clinical presentation (‘spinal MS’), course (primary progressive MS without relapses vs. relapsing-remitting MS), severity and prognosis (‘benign MS’); (iii) MRI studies have suggested different lesion types in MS; and (iv) treatment trials have found ‘non-responders’, i.e. patients in whom drugs shown to be effective in the majority of patients with MS were of no benefit. In accordance with that hypothesis, numerous patients previously diagnosed as having variants of MS or ‘opticospinal MS’ based on the current clinicoradiological consensus criteria were found over the past decade to have newly discovered humorally mediated diseases, pathophysiologically distinct from MS, that are now termed AQP4-IgG-positive ‘neuromyelitis optica spectrum’ disorder (NMOSD) [28‐33] and MOG-IgG-positive encephalomyelitis (EM) [17, 34‐42]. Of note, many of patients with AQP4-IgG-positive NMO or MOG-IgG-positive EM had previously been wrongly diagnosed with MS due to a significant overlap in clinical presentation and clinical criteria and, in consequence, had been wrongly treated with drugs approved for MS but not for NMO or MOG-EM [17, 34‐36, 43‐47]. In a large European cohort, more than 40% of AQP4-IgG-positive patients with NMOSD had been previously misdiagnosed with MS [43]. Similarly, McDonald’s clinicoradiological criteria or Barkhofs’s radiological for MS were met by 33 and 15%, respectively, of all MOG-IgG-positive patients in a recent study [35]. Wrong diagnosis and, accordingly, false treatment for MS may have caused disease exacerbation and worse outcome in some of those patients, underlining the clinical importance of studies investigating potential heterogeneity in MS [45‐47].

AQP4-IgG-positive NMO lesions, MOG-IgG-positive EM lesions and pattern II MS lesions share important histopathological similarities in that all three are characterized by antibody and complement deposits. It is therefore of particular note that many of the CSF findings from patients with pattern II lesions were more similar to what has been reported in AQP4-IgG-positive NMO [43, 48, 49] and MOG-IgG-positive EM [17, 34‐36] than to what was found in patients with pattern I lesions in our study (Tables 1, 2, 3, 4, 5, 6, 7, and 8). However, the majority of patients with pattern II and pattern III lesions are negative for AQP4-IgG and MOG-IgG, as were all 10 patients with pattern II or III lesions and available serum samples in the present study [18, 50, 51], suggesting a potential role of other, so far unknown autoantibodies in this condition. In contrast, the CSF findings associated with pattern I lesions were much more in line with what one would expect in patients with typical MS.

Of interest, AQP4-IgG-positive NMO is characterized by a marked female predominance (male to female ratio ~1:10–12) [43]; in contrast, the male to female ratio was 1:2.2 in the pattern II patients and thus more similar to what has been reported in MS and in MOG-IgG-positive EM [35].

In Germany, ≥95% of all MS patients are positive for CSF-restricted OCB [8, 10, 19]. The fact that most pattern II and III patients had no CSF-restricted OCB in our study therefore implies that pattern II and III MS cannot account for the majority of patients with MS. With most pattern II and III patients belonging to the small subgroup of <5% of OCB-negative MS cases, pattern II MS and pattern III MS are probably rare conditions.

This seems to be in contrast to histopathological studies that reported a lower proportion of pattern I cases. However, there are several reasons why pattern II and III cases may be overrepresented in neuropathological cohorts:

Our results indicate that the proportion of patients with type II and type III lesions may be particularly high among OCB-negative patients diagnosed with MS. While only 2–10% of patients with MS are negative for OCB according to the literature, this subset is not small in absolute numbers, given the high prevalence of MS in some Western populations (e.g. ~2.3 million patients worldwide; ~140,000 patients in Germany). Given that fact and considering that differences in pathophysiology may well translate into different treatment requirements, as already shown in AQP4-IgG-positive NMO [47] and suggested for MOG-IgG-positive EM [34, 35], studies aiming at enhancing our understanding of the immunopathophysiology of pattern II and III lesions seem highly warranted.

Importantly, the frequency of OCB has been reported to increase with latitude [53, 54]. Whether this implies a higher proportion of patients with ‘pattern I’ lesions at higher latitudes is currently unknown but deserves to be addressed in future studies.

We acknowledge that our study has both strengths and limitations. While we count the high number of CSF samples included (n = 68) and the high number of CSF parameters analysed among the strengths of our study, the retrospective and exploratory study design is a potential limitation. However, prospective studies would be extremely difficult or even impossible to perform given that brain biopsies are only very rarely performed in patients with MS and that lumbar puncture is not anymore required to make the diagnosis of MS according to the current international diagnostic criteria [3].

In summary, the present study provides additional, strong evidence for pattern I MS on the one hand and pattern II MS and pattern III MS on the other hand being distinct entities by demonstrating significant differences in CSF findings between patients with pattern I lesions and patients with pattern II or pattern III lesions, especially with regard to intrathecal IgG synthesis. Of particular note, the CSF profiles present in the pattern II/III subgroup were more similar to those reported in AQP4-IgG-positive NMO and MOG-IgG-positive EM than to those classically considered typical for MS. Further studies are now warranted to confirm our findings in larger, international cohorts. Such studies need to take into account the recently reported increase in frequency of CSF oligoclonal banding in MS with latitude [53, 54].