Mild Encephalopathy With Reversible Splenial Lesion (Mers) In An Adult Patient With Atypical Presentation

In patients with MERS, encephalopathy is characterized by altered consciousness, delirium, and seizures. Patients often present with a prodromal period, most frequently characterized by fever, followed by headache, vomiting, and diarrhea [5]. In a recent meta-analysis by Chiara et al., it was shown that in a sample of 51 adult patients diagnosed with MERS 88% experienced prodromal symptoms, mainly fever (78%) and/or flu-like symptoms (42%). Headache was the most frequent presenting symptom, present in 25 (50%) patients and in 10 (20%), it was the only neurological symptom. Seizures and altered consciousness were present in 11 (22%) patients, and delirium was observed in 8 (16%) patients [6]. In the presented case, we can observe an atypical presentation of MERS compared to what is described in the literature, as there were no neurological symptoms, with only the so-called prodromal stage being present.

Since the patient was hospitalized and the diagnosis was made based on criteria that included lesion reversibility (Table 1) [7], it was necessary to pursue differential diagnoses that might require alternative therapies. Among those highlighted in the literature are lymphoma, infarction, tumors (lipoma, glioblastoma), multiple sclerosis, Marchiafava-Bignami disease, diffuse axonal injury associated with trauma, posterior reversible encephalopathy syndrome (PRES), acute encephalopathy associated with intravenous immunoglobulin treatment, alcoholism, malnutrition, and myelin disorders (Krabbe disease, X-linked adrenoleukodystrophy) [1]. However, these were clinically and radiologically ruled out in our patient.

Although the described case was not associated with a specific etiological agent, the clinical presentation of a febrile syndrome with nonspecific symptoms suggests that the pathology could be attributed to an infectious event whose etiological agent was not included in the panels available at our institution. Toxicity or withdrawal from AEDs or acute metabolic disturbances were ruled out. Reported literature indicates that up to 73% of cases have an unknown etiology, with infectious origins being the most frequently associated [6].

The pathophysiology of these reversible splenial lesions of the corpus callosum is not well understood due to the diversity of etiologies. It is possible that several mechanisms are responsible, such as intramyelinic edema, oxidative stress, autoimmune processes, inflammation, cytotoxic edema characterized by swelling of neurons and glial cells with reduced extracellular space, and vasogenic edema [8].

In type 1 MERS, the lesions are limited to the splenium (oval or band-shaped), as seen in our clinical case, whereas in type 2 MERS, the lesions are not limited to the splenium. The clinical and radiological outcome is usually favorable, with clinical improvement occurring within 1 to 2 days, while radiological improvement occurs within 10 days to 4 months [9], although more typically the lesions resolve within two weeks. The follow up MRI in the presented case was performed one month after the initial imaging, which no longer showed the cytotoxic lesion. In rare cases, especially those with type 2 MERS lesions, neurological sequelae may develop, with type 1 lesions having the best prognosis [9].

The therapeutic approach is based on symptomatic treatment, although if an infectious agent is found, its treatment may change the prognosis [1]. Antivirals, corticosteroids, and immunoglobulins have been used, with a good response in all cases. However, their efficacy remains uncertain given the reversibility of the condition [2]. In this case presented, no specific symptomatic treatment was required.