[17, 18].
Moreover, most cases of reversible lesions demonstrate the evidence that cytotoxic edema of the SCC is an important mechanism in this syndrome[28]. Miyata R et al [16], reported that patients with MERS has an elevated IL-6 and IL-10 levels in CSF. Cytotoxic edema in the neurons, astrocytes, and oligodendrocytes of the SCC, caused by cytokines, may offer the best explanation. Recently, these lesions have been called cytotoxic lesions of the corpus callosum or CLOCC lesions [28, 29]. This could explain the elevated white cells in the CSF as it is the case of our patient. A recent review study [19] found that more than half (15/23) cases had elevated white cells in the CSF. Even if we take all these hypotheses into account, MERS still be a rare syndrome with unclear pathogenesis and none of the existing hypotheses may explain why MERS specially involves the site splenium.
In addition, serum sodium levels were significantly lower in patients with MERS than in age matched controls. These data support the hypothesis that a transient cerebral edema may develop as a result of hyponatremia [17].
RTX is a murine/human‐chimeric monoclonal antibody that depletes CD20+ B cells through both cell‐mediated and complement mediated cytotoxic effects [30]. It is widely used in malignancy and immune‐mediated diseases in combination with corticosteroids and other immunosuppressive drugs.
RTX is also effective for both induction therapy and treatment of relapses in IgG4-RD specially in nephrologic flare refractory to corticosteroids [31]. Its administration rarely causes serious neurologic adverse events. However, it was reported to lead to complement activation, cell lysis and subsequent massive release of cytokines, culminating in cytokine release syndrome and systemic inflammatory response syndrome [32-35]. This could, in part, explain the early development of MERS after rituximab in our patient. But MERS induced by Rituximab has never been reported before.
However, Posterior reversible encephalopathy syndrome (PRES), which may be a differential diagnoses for MERS, has been reported to be related to RTX [3].
PRES is a rare clinical disorder which has nearly clinical symptoms to MERS. It manifests also with headache, convulsions, altered level of consciousness and reversible cerebral edema. It is also a reversible disorder that requires rapid diagnosis by demonstrating the presence of characteristic vasogenic edema on brain MRI in the appropriate clinical context [36, 37].
Progressive multifocal leukoencephalopathy (LEMP) after RTX, which is a rare opportunistic infection due to reactivation of JC virus into the central nervous system, is described [38].
Acute disseminated encephalomyelitis (ADEM) is being the main differential radiologic diagnosis of MERS [39] but RTX is effective for this disease [40].
The neurological manifestations presented by the patient cannot also be related to his underlying disease. IgG4-related disease can involve nearly any organ system, including the central and peripheral nervous systems but MERS has never been reported [41].
Furthermore, MERS is a rare disease and evidence on the therapeutic approaches is currently not yet available. Methylprednisolone pulse therapy and IVIG were prescribed in MERS patients without any evidence of efficacy of these treatments. However, many patients without methylprednisolone pulse therapy or IVIG recovered clinically completely, which suggests that those treatments may not be necessary[42]. Our patient was treated by methylprednisolone pulse therapy and IVIG as we had a severe neurological involvement and we were face an auto immune disease (IgG4-RD).