Introduction
Mild encephalitis/encephalopathy with a reversible splenial lesion syndrome (MERS) is a rare clinical-radiological syndrome. It was first identified by Carlos Garcia-Monco [1] in 2011. The most common neurological symptoms are behavioral changes, altered consciousness and seizures [2]. The diagnosis is based on Brain magnetic resonance imagings (MRIs) showing a transient anomalies mainly in the corpus callosum or sometimes extending to adjacent parenchyma [1]. This syndrome mostly recovers without treatment [1]. Biotherapy was reported to be efficient in MERS in some cases. [3, 4] This syndrome was reported in patients with viral infections, particularly rotavirus, herpes simplex virus, adenovirus, coxsackie virus, echoviruses, mumps, influenza A/B virus, and recently SARS CoV-2 [5-12]. In few cases MERS was induced by some drugs such ipilimumab [13] and mumps vaccination [14]. Here, we describe an original case of MERS appearing few hours after RTX treatment in a patient with IgG4-RD.