Delirious behavior in influenza is associated with a reversible splenial lesion

Metabolic changes assessed by 1H MR spectroscopy in the corpus callosum of post-COVID patients

OBJECTIVE

Many patients with long COVID experience neurological and psychological symptoms. Signal abnormalities on MR images in the corpus callosum have been reported. Knowledge about the metabolic profile in the splenium of the corpus callosum (CCS) may contribute to a better understanding of the pathophysiology of long COVID.

MATERIALS AND METHODS

Eighty-one subjects underwent proton MR spectroscopy examination. The metabolic concentrations of total N-acetylaspartate (NAA), choline-containing compounds (Cho), total creatine (Cr), myo-inositol (mI), and NAA/Cho in the CCS were statistically compared in the group of patients containing 58 subjects with positive IgG COVID-19 antibodies or positive SARS-CoV-2 qPCR test at least two months before the MR and the group of healthy controls containing 23 subjects with negative IgG antibodies.

RESULTS

An age-dependent effect of SARS-CoV-2 on Cho concentrations in the CCS has been observed. Considering the subjective threshold of age = 40 years, older patients showed significantly increased Cho concentrations in the CCS than older healthy controls (p = 0.02). NAA, Cr, and mI were unchanged. All metabolite concentrations in the CCS of younger post-COVID-19 patients remained unaffected by SARS-CoV-2. Cho did not show any difference between symptomatic and asymptomatic patients (p = 0.91).

DISCUSSION

Our results suggest that SARS-CoV-2 disproportionately increases Cho concentration in the CCS among older post-COVID-19 patients compared to younger ones. The observed changes in Cho may be related to the microstructural reorganization in the CCS also reported in diffusion measurements rather than increased membrane turnover. These changes do not seem to be related to neuropsychological problems of the post-COVID-19 patients. Further metabolic studies are recommended to confirm these observations.

Reversible splenial lesions during febrile illness with or without white matter lesions

OBJECTIVE

Reversible splenium lesions during febrile illness (RESLEF) are found in a spectrum. There are two types of corpus callosum (CC) lesions: CC-only type, with limited lesions and the CC (+) type, with extensive white-matter lesions. This retrospective study aimed to describe the differences in clinical findings between CC-only and CC (+) lesions and the association between onset age and clinico-radiological features in RESLEF.

METHODS

Fifty-two episodes of CC-only or CC (+) lesions accompanied by neurological symptoms, e.g., seizures, delirious behavior (DB), and disturbance of consciousness (DC), from January 2008 to October 2019 were included. We analyzed the etiology (pathogen), clinical course, laboratory data, magnetic resonance imaging and electroencephalography findings, therapy, and prognosis.

RESULTS

The rate of DC in the CC (+) was significantly higher than that in the CC-only group (5/6 [83%] vs 7/46 [15%]; p = 0.0016). The median number of seizures in the CC (+) was also significantly higher than that in the CC-only group (4 [0-7] vs 0 [0-7]; p = 0.034). Further, in RESLEF, the median onset age (months) in the seizure was significantly lower than that in the no-seizure group (39 [12-74] vs 83 [28-174]; p = 0.0007). The median onset age (months) in the DB was significantly higher than that in the no-DB group (74.5 [26-174] vs 28 [12-139]; p = 0.003).

CONCLUSIONS

In RESLEF, CC (+) is a more severe neurological symptom than CC-only. Furthermore, the onset age is related to the type of neurological symptoms that appear.

The splenium of the corpus callosum: embryology, anatomy, function and imaging with pathophysiological hypothesis

BACKGROUND AND PURPOSE

The splenium of the corpus callosum is the most posterior part of the corpus callosum. Its embryological development, anatomy, vascularization, function, imaging of pathology, possible pathophysiological mechanisms by which pathology may develop and the clinical consequences are discussed.

METHODS

A literature-based description is provided on development, anatomy and function. MR and CT images are used to demonstrate pathology. The majority of pathology, known to affect the splenium, and the clinical effects are described in three subsections: (A) limited to the splenium, with elaboration on pathophysiology of reversible splenial lesions, (B) pathology in the cerebral white matter extending into or deriving from the splenium, with special emphasis on tumors, and (C) splenial involvement in generalized conditions affecting the entire brain, with a hypothesis for pathophysiological mechanisms for the different diseases.

RESULTS

The development of the splenium is preceded by the formation of the hippocampal commissure. It is bordered by the falx and the tentorium and is perfused by the anterior and posterior circulation. It contains different caliber axonal fibers and the most compact area of callosal glial cells. These findings may explain the affinity of specific forms of pathology for this region. The fibers interconnect the temporal and occipital regions of both hemispheres reciprocally and are important in language, visuospatial information transfer and behavior. Acquired pathology may lead to changes in consciousness.

CONCLUSION

The development, location, fiber composition and vascularization of the splenium make it vulnerable to specific pathological processes. It appears to play an important role in consciousness.

MERS associated with bacterial translocation in a pediatric patient with congenital portal vein hypoplasia: A case report

A case of mild encephalitis/encephalopathy with a reversible splenial lesion (MERS) in a female child who developed bacterial translocation from a congenital portal vein hypoplasia is reported. The patient was diagnosed as having portal hypertension after examinations and laboratory results showing splenomegaly and thrombocytopenia at the age of 1 year. The patient required three endoscopic variceal ligation (EVL) surgeries before the age of 9 due to development of multiple esophageal varices. After the second and third EVL procedures, she developed septicemia, possibly due to bacterial translocation associated with the administration of general anesthesia. The day after the third EVL, the patient presented with high fever and neurological disturbances (altered consciousness). Magnetic resonance imaging detected abnormal intensities in the corpus callosum ampulla and cerebral white matter, which suggested a diagnosis of MERS type 2. Considering this clinical course, the possible association between bacterial translocation and MERS in a patient with congenital portal vein hypoplasia and portal hypertension is discussed.

Delirium Upon Presentation to the Pediatric Emergency Department: A Case Series

The following cases describe children who presented to the emergency department (ED) with a constellation of symptoms consistent with delirium. In each case, there was no identified inciting cause (eg, fever, medications) other than the presence of influenza. All children had variable workups, with 2 children undergoing extensive neurologic evaluation and testing. Clinical recognition of delirium in the pediatric acute care setting can be challenging, but heightened awareness by ED and primary care physicians may lead to earlier diagnosis, prevent unwarranted investigations, and decrease hospitalization. Children with influenza may be at increased risk of developing delirium. A prospective study to assess the prevalence of delirium in pediatric patients presenting to the ED with influenza is warranted.

Longitudinal diffusion changes following postoperative delirium in older people without dementia

OBJECTIVE

To investigate the effect of postoperative delirium on longitudinal brain microstructural changes, as measured by diffusion tensor imaging.

METHODS

We studied a subset of the larger Successful Aging after Elective Surgery (SAGES) study cohort of older adults (≥70 years) without dementia undergoing elective surgery: 113 participants who had diffusion tensor imaging before and 1 year after surgery. Postoperative delirium severity and occurrence were assessed during the hospital stay using the Confusion Assessment Method and a validated chart review method. We investigated the association of delirium severity and occurrence with longitudinal diffusion changes across 1 year, adjusting for age, sex, vascular comorbidity, and baseline cognitive performance. We also assessed the association between changes in diffusion and cognitive performance across the 1-year follow-up period, adjusting for age, sex, education, and baseline cognitive performance.

RESULTS

Postoperative delirium occurred in 25 participants (22%). Delirium severity and occurrence were associated with longitudinal diffusion changes in the periventricular, frontal, and temporal white matter. Diffusion changes were also associated with changes in cognitive performance across 1 year, although the cognitive changes did not show significant association with delirium severity or occurrence.

CONCLUSIONS

Our study raises the possibility that delirium has an effect on the development of brain microstructural abnormalities, which may reflect brain changes underlying cognitive trajectories. Future studies are warranted to clarify whether delirium is the driving factor of the observed changes or rather a correlate of a vulnerable brain that is at high risk for neurodegenerative processes.

Differential diagnosis of delirious behavior in children with influenza

Delirious behavior (DB) in children infected with influenza virus is an important symptom associated with encephalopathy. As children with influenza-associated DB with encephalopathy may require therapy whereas children with influenza-associated DB without encephalopathy do not, distinguishing between these conditions is essential. To clarify these differences and identify the most common features of acute encephalopathy, we retrospectively reviewed the clinical course, laboratory data, magnetic resonance imaging (MRI) and electroencephalography (EEG) findings, therapy, and prognosis of 48 children with influenza exhibiting DB. Of the 48 children, 37 and 11 were diagnosed with influenza A and B, respectively. Moreover, 40 were diagnosed with DB without encephalopathy (DBNE group) and 8, with DB with encephalopathy (DBE group). Reversible splenial lesion (RESLE) was detected in 7 patients in the DBNE group, mild encephalitis/encephalopathy with a reversible splenial lesion (MERS) in 2 patients, and a mild form of acute encephalopathy with biphasic seizures and late reduced diffusion in 1 patient in the DBE group. Serum sodium levels <136mEq/L were observed in 28 cases. Disturbance of consciousness was observed in 25 cases, seizure in 20, and slow waves on EEG in 22. Methylprednisolone pulse therapy was administered in 8 cases. No cases of neurological sequelae were observed. Although most of the clinico-radiological features of the DBNE and DBE groups did not differ substantially, marked differences were observed in the age at onset, initial neurological symptoms, duration of DB, rate of seizure, and slowing of background activity on EEG. These differences should be considered when distinguishing between DBNE and DBE in children.

Influenza encephalopathy and related neuropsychiatric syndromes

Influenza is occasionally complicated by CNS disorders, in particular impairment of consciousness. Severe disorders encompass multiple, distinct syndromes manifesting acute encephalopathy, whereas mild disorders represent multiple, ill-defined neuropsychiatric syndromes. Acute encephalopathy is manifested with seizures and coma, with or without multi-organ involvement. The outcome varies from death or neurologic sequelae to recovery and differs among syndromes. Transient neuropsychiatric disorders are manifested with delirium and/or abnormal behavior. There also are multiple syndromes. The outcome is usually favorable, although occasional fatal accidents warrant caution.

Clinico-radiological spectrum of reversible splenial lesions in children

Recently, many cases of children presenting reversible splenial lesions during febrile illness (RESLEF) have been reported; however, their overall clinico-radiological features are unclear. To describe the clinico-radiological features, we retrospectively reviewed the etiology (pathogen), clinical course, laboratory data, magnetic resonance imaging and electroencephalography (EEG) findings, therapy, and prognosis of 23 episodes in 22 children (1 child recurred) who presented neurological symptoms, with RESLEF. The etiologies (pathogens) varied. Seizure occurred in 7 episodes, disturbance of consciousness (DC) in 13, and delirious behavior in 18. Serum sodium levels <136 mEq/L were observed in 18 episodes. Lesions outside the splenium were found in 4 cases. Slow waves were observed on EEG in 10 episodes. Methylprednisolone pulse therapy was given in 7 cases. No case resulted in neurological sequelae. Among 23 episodes, clinically mild encephalitis/encephalopathy with a reversible splenial lesion (MERS) was diagnosed in 6 episodes, whereas non-MERS was observed in 17 episodes. No difference was observed in almost all the clinico-radiological features' data between the 2 groups. The largest differences were observed in the rate of purposeless movement, DC, extension of the abnormal lesions outside the splenium, and marked slowing of background activity on EEG. RESLEF exhibit a spectrum of clinico-radiological features. These results suggest that non-MERS and MERS both are a part of a larger pathological condition, which we have termed as RESLEF spectrum syndrome. Given the view that such a syndrome exists, the clinical characteristics and position of non-MERS and MERS become clear.

Delirious behavior or mild reduction of consciousness mimicking influenza-associated encephalopathy

BACKGROUND

During the A/H1N1 pandemic, patients suffered from impaired consciousness. They were suspected of or diagnosed as having influenza-associated encephalopathy (IAE) in an emergency situation. Their symptoms resembled those of a recently described 'unique clinical group', which were reported to have a favorable prognosis.

METHODS

We retrospectively examined 46 patients and divided them into two groups. Group IC contained the 26 patients with persisting impaired consciousness. The remainder of the patients were categorized into group R, consisting of patients with only neurological symptoms without impaired consciousness.

RESULTS

Male predominance (22 male/four female) was noted in group IC. Patient age ranged from 5 to 12 years old (mean ± SD, 7.7 ± 2.3 years). Impaired consciousness such as delirious behavior or mild reduction of consciousness lasted continuously or intermittently from 5 min to 2.5 days. On electroencephalogram, semi-rhythmic high-voltage slow waves in the parieto-occipital regions and diffuse high-voltage slow waves were observed in eight and in two patients, respectively. In group R, there was no gender predominance. Patient age ranged from 1 to 9 years old (mean ± SD, 4.1 ± 2.5 years). All group R patients were clinically diagnosed with febrile seizure.

CONCLUSIONS

Some of the characteristics in group IC resembled those of the unique clinical group, and are part of a continuous clinical spectrum. Some patients may have favorable outcome without specific treatment.

Neurologic aspects of influenza viruses

Although influenza A and B viruses are primarily known as respiratory viruses and mainly infected only the upper respiratory tract in humans, patients with influenza often develop signs and symptoms that are not due to the respiratory system. Frequently individuals with influenza develop headaches, meningismus, and even seizures in addition to their typical respiratory symptoms. In the past decades, influenza viruses have also been associated with serious non-respiratory signs. The famous 1918 strain of influenza was associated with von Economo's encephalitis lethargica and postencephalitic parkinsonism. In the 1960s influenza virus infections in children were associated with Reye's syndrome characterized often by fatty non-inflammatory hepatic disease and an encephalopathy with marked non-inflammatory cerebral edema. Intermittently children with influenza develop focal myalgia and myositis. Guillain–Barré syndrome was epidemiologically associated with the 1978 killed influenza vaccine but not subsequent vaccines. Although occasional children with influenza have developed encephalopathy, from 2000 through 2004 there was an increase in the number of serious cases of acute necrotizing encephalopathy accompanying infection with the influenza A 2009 strain. The current H5N1 strain of bird influenza occasionally infects humans with a high mortality rate and some appear to have central nervous signs. This chapter explores what is known about these influenza neurologic associations.

A Case of Mild Encephalopathy with a Reversible Splenial Lesion Associated with G5P[6]Rotavirus Infection

We report a case of mild encephalopathy with a reversible splenial lesion (MERS) associated with acute gastroenteritis caused by rotavirus (RV) infection. The patient (male, 4 years and 3 months old) was admitted to our hospital for diarrhea and afebrile seizures. Head MRI revealed a hyperintense signal in the splenium of the corpus callosum on DWI and a hypointense signal on the ADC-map. After awakening from sedation, the patient's disturbance of consciousness improved. On day 5 after admission of the illness, the patient was discharged from the hospital in a good condition. Electroencephalography on day 2 after admission was normal. On day 8 of admission, head MRI revealed that the splenial lesion had disappeared. RV antigen-positive stools suggested that RV had caused MERS. This RV genotype was considered to be G5P[6]; it may have spread to humans as a strain reassortment through substitution of porcine RV into human RV gene segments. This extremely rare genotype was detected first in Japan and is not covered by existing vaccines; this is the first sample isolated from encephalopathy patients. Few reports have investigated RV genotypes in encephalopathy; we believe that this case is valuable for studying the relationship between genotypes and clinical symptoms.

[A case of influenza pneumonia following pneumococcal infection in an adult patient with concurrent encephalopathy with a lesion in the splenium of the corpus callosum]

A 35-year-old male patient had a fever, cough, and other symptoms since the end of December 2010. The patient then developed a high fever and decreased SpO2, suggesting possible pneumonia. The patient was admitted to our hospital on the 6th day of illness. Chest computed tomography revealed multiple infiltrative shadows and ground-glass opacities distributed in a patchy pattern in the bilateral lungs. An atypical pneumonia was suspected, and we initiated antibiotic treatment with minocycline. However, the patient developed consciousness disturbance in the afternoon of the 7th day of illness. The high fever persisted, suggesting the patient's poor response to minocycline treatment, which was then replaced with ciprofloxacin and imipenem/cilastatin on the 8th day of illness. Streptococcus pneumoniae was detected in the blood culture bottles submitted at the time of admission. A head magnetic resonance imaging performed on that day showed a high intensity area in the splenium of the corpus callosum, leading to a diagnosis of encephalopathy. Methylprednisolone pulse therapy and gamma globulin treatment were initiated. The patient then recovered consciousness gradually with improvement of inflammatory responses and imaging findings. Subsequently, an influenza virus (H1N1) antibody level was found to have increased from less than 10 times to 640 times. Thus, it was determined that the patient's pneumonia and encephalopathy were attributable to the influenza A (H1N1) pdm09 virus during the flu season and Streptcoccal infection. Combination therapy, such as steroid pulse treatment, appropriate antibiotics and gamma globulin preparation was effective for both the flu-induced mixed pneumonia and encephalopathy in this patient.

Influenza-related postinfectious encephalomyelitis complicated by a perforated peptic ulcer

Influenza virus infection is extremely common and raises global concern due to the increasing prevalence of pandemic H1N1 infection. Influenza may occasionally be associated with neurologic complications and, also, rarely with gastrointestinal complications. Here, we report a rare case complicated with appendicitis, duodenum perforation, and transient delirious behavior after influenza A viral infection in a pediatric patient aged 14 years. The transient delirious behavior could be attributed to postinfectious encephalopathy. The perforated peptic ulcer could have resulted from influenza infection, could have been an adverse event related to oseltamivir administration, or could have been a complication of preceding gastroenteritis. Our case highlights the importance of pediatric healthcare workers to be aware of possible complications arising from both influenza infection and oseltamivir therapy, even though some of these complications may be relatively rare.

Mild encephalopathy with splenial lesion and parainfluenza virus infection

Mild encephalopathy with reversible splenial lesions has mainly been associated with influenza A and B virus infection. Patients present with neurologic symptoms 1 to 3 days after a prodromal illness and recover completely within a few days. Magnetic resonance imaging typically shows reversible lesions with reduced diffusion in the corpus callosum, predominantly in the splenium. We report on a 5-year old Caucasian boy who was referred with recurrent seizures and decreased level of consciousness after a 2-day prodromal fever and cough. Magnetic resonance imaging showed cytotoxic edema of the entire corpus callosum and the adjacent periventricular white matter with diffusion restriction and faint T(2)-hyperintensity. Parainfluenza virus type 1-3 infection was documented by direct immunofluorescence in the initial nasopharyngeal swab, but polymerase chain reaction for parainfluenza virus type 1-4 in the cerebrospinal fluid remained negative. This is-to our knowledge-the first description of mild encephalopathy with reversible splenial lesions in association with parainfluenza virus infection. The pathogenesis of mild encephalopathy with reversible splenial lesions, however, still remains unclear, and further studies investigating detailed mechanisms that lead to the typical brain lesions are warranted.

Post-marketing assessment of neuropsychiatric adverse events in influenza patients treated with oseltamivir: an updated review

A 2008 review by our group concluded that the risk of neuropsychiatric adverse events (NPAEs) in influenza patients was not increased by oseltamivir exposure, and did not identify any mechanism by which oseltamivir or its metabolites could cause or worsen such events. The current article reviews new information on this topic. Between September 16, 2007 and May 15, 2010, 1,805 spontaneously-reported NPAEs were identified in 1,330 patients receiving oseltamivir: 767 (42.5%) from Japan, 296 (16.4%) from the USA, and 742 (41.1%) from other countries. NPAEs were more common in children: 1,072 (59.4%) events were in those aged ≤16 years. NPAEs often occurred within 48 h of treatment initiation (953 events; 52.8%). Nearly half of the events were serious in nature (838; 46.4%). The three largest categories of events were abnormal behavior (457 events, 25.3%), miscellaneous psychiatric events (370; 20.5%), and delusions/perceptual disturbances (316 events, 17.5%). A total of 1,545 events (85.6%) in eight different categories were considered to be delirium or delirium-like. Twenty-eight suicide-related events were reported. A US healthcare claims database analysis showed that the risk of NPAEs in 7,798 oseltamivir-treated patients was no higher than that in 10,411 patients not on antivirals, but a study on oseltamivir and abnormal behavior in Japan was less conclusive. NPAE frequency in oseltamivir-exposed Japanese and Taiwanese children with influenza was the same as in unexposed children. New analysis of the UK General Practice Research Database showed that the relative adjusted risk of NPAEs in influenza patients was 2.18-times higher than in the general population. Other epidemiology studies report frequent occurrence of encephalitis and similar disorders in influenza patients independently of oseltamivir exposure. The new data support the findings of the original assessment. Evidence suggests that influenza-related encephalopathies are caused by influenza-induced inflammatory responses, but more work is needed to confirm the underlying mechanisms.

Fornix injury in a patient with rotavirus encephalopathy: diffusion tensor tractography study

Rotavirus encephalopathy (RE) is a benign afebrile seizure associated with acute gastroenteritis caused by rotavirus infection. We investigated the diffusion tensor tractography (DTT) findings of a patient with RE. The patient was a 30-month-old female that had experienced a brief, generalized convulsive seizure. On the day of admission, the patient had vomiting and experienced watery diarrhea. Her stool was positive for rotavirus antigen. At onset, the patient displayed a drowsy and delirious mental status; later, a splenial lesion of the corpus callosum was found on MRI. One week later, the patient's condition improved and the splenial lesion had disappeared by conventional MRI. Initial DTI showed decreased fractional anisotropy (FA) values of fornix, as well as of the corpus callosum. A follow-up DTT showed a restored interrupted right fonical crus and increased FA values of corpus callosum and fornix. These results highlight the implications of the probability of not only a corpus callosum injury, but a fornix injury as well, in this patient with RE.

Late delirious behavior with 2009 H1N1 influenza: mild autoimmune-mediated encephalitis?

Delirious behavior associated with influenza usually has an onset within a few days after fever and lasts <24 hours. As we encountered several patients with 2009 H1N1 influenza who presented with late-onset and long-standing delirious behavior, we retrospectively evaluated the clinical, radiologic, and laboratory features to elucidate the possible pathophysiology. This information was collected on 5 previously healthy patients (2 boys and 3 girls, aged 10-15 years) with 2009 H1N1 influenza who presented with late onset (>3 days after fever) and long-standing (>48 hours) delirious behavior. Each exhibited mild to moderate drowsiness between the episodes of delirious behavior. Electroencephalography was normal except for 1 patient with high voltage and slow activity bilaterally in the occipital regions. Brain MRI was normal. The outcome was excellent with no neurologic sequel in 4 of the 5 patients. In all 5 patients, autoantibodies against N-methyl-D-aspartate type glutamate receptor were elevated or positive in cerebrospinal fluid or serum; the autoantibody levels normalized in the 3 patients who had follow-up studies. This study indicates that 2009 H1N1 influenza has a tendency to cause late-onset and long-standing delirious behavior, at least in Japanese children. Mild autoimmune-mediated encephalitis should be considered as an underlying cause.

A case of clinically mild encephalitis with a reversible splenial lesion (MERS) after mumps vaccination

We describe for the first time an 8-year-old male patient who demonstrated clinically mild encephalitis with a reversible splenial lesion after mumps vaccination. He suffered from transient hallucinations, nuchal rigidity, and inappropriate antidiuretic hormone secretion syndrome. On the 5th day of admission, his head MRI showed symmetrical high-signal-intensity lesions on T2, FLAIR, and diffusion-weighted images in the splenium of the corpus callosum and in the periventricular white matter, while an apparent diffusion coefficient map showed reduced diffusion. The images were not enhanced by gadolinium. Follow-up MRI on the 16th day of admission revealed none of these abnormalities. His serum IgM and IgG antibodies against the mumps virus were positive according to an enzyme immunoassay. Mumps Torii vaccine strain was isolated from the patient's cerebrospinal fluid. Previous reports demonstrated that transient delirious behavior, the syndrome of inappropriate antidiuretic hormone secretion, and good prognosis were the main clinical features of mild encephalitis with a reversible splenial lesion. This case shows that mild encephalitis with a reversible splenial lesion could occur after mumps vaccination.

Two newly proposed infectious encephalitis/encephalopathy syndromes

Two newly proposed infectious encephalitis/encephalopathy syndromes, in which magnetic resonance imaging (MRI) is essential for the diagnosis, have been reviewed. Acute encephalopathy with biphasic seizures and late reduced diffusion (AESD) is reported only in East Asian infants, characterized by a febrile seizure (usually >30 min) as the initial neurological symptom on day 1, followed by secondary seizures at day 4 to 6; affected children display variable levels of neurological sequelae. MRI shows no acute abnormality during the first two days; reduced diffusion appears in the frontal or fronto-parietal subcortical white matter during days 3 to 9, then disappears between days 9 and 25. Excitotoxic injury with delayed neuronal death is hypothesized as a possible mechanism based on MR spectroscopic findings. Clinically mild encephalitis/encephalopathy with a reversible splenial lesion (MERS) is characterized by a reversible lesion with homogeneously reduced diffusion in the corpus callosum (at least involving the splenium), sometimes associated with symmetrical white matter lesions. The most common neurological symptom is delirious behavior, followed by consciousness disturbance, and seizures, all of which completely recover within a month. The reason for the transiently reduced diffusion within the lesions is unknown; possibilities that have been postulated include intramyelinic edema, interstitial edema in tightly packed fibers, and a transient inflammatory infiltrate.