ラスムッセン脳炎

The taiga tick Ixodes persulcatus (Schulze, 1930) (Acari, Ixodidae), widespread in the northern Palearctic, is the vector of dangerous human pathogens including tick-borne encephalitis virus. Knowledge of its ecology is important for minimising tick bite exposure risk. We studied the diel activity of male and female I. persulcatus in the north of the range (Karelia, Russian Federation) and tested its relationship with environmental factors including temperature, relative humidity and light intensity. The field experiment was conducted in May-June 2024. Cages with unfed adult ticks (males and females) were placed in three different biotopes, and their activity was assessed every two hours. Tick activity could be described by a bimodal curve, with a peak in the morning and in the evening. Diel activity rhythms were somewhat different in male and female ticks, with females questing longer than males. Relative humidity was the key determinant of questing duration. Weather changes accompanied by decreasing atmospheric pressure, as well as rain, reduced tick activity. The greatest tick bite exposure risk in Karelia is observed from mid-May to early June, when the temperature ranges from 10 °C to 20 °C and relative humidity exceeds 70%.

N-methyl-D-aspartate (NMDA) receptor encephalitis stands as the most common form of autoimmune encephalitis in young adults, characterized by a spectrum of distressing symptoms such as seizures, behavioral disruptions, autonomic dysfunction, and memory impairment. We present a noteworthy case involving a young adult male exhibiting seizures and renal failure, initially prompting an evaluation for vasculitis, hyperuricemia-induced acute kidney injury (AKI), and rhabdomyolysis-induced AKI. However, subsequent findings revealed the presence of NMDA receptor antibodies, and a renal biopsy confirmed tubulointerstitial nephritis. This case sheds light on the association between renal failure and NMDA receptor antibody-associated encephalitis, marking a rare instance in our knowledge.

Myelin oligodendrocyte glycoprotein (MOG) antibody-associated disease (MOGAD) is a rare autoimmune demyelinating disorder of the central nervous system that can present with varied neurological symptoms. While commonly mistaken for multiple sclerosis or neuromyelitis optica spectrum disorders, MOGAD can also mimic cerebrovascular events, posing a diagnostic challenge. We report a case of a 30-year-old male who initially presented with acute-onset left-sided hemiplegia and right facial palsy, raising suspicion of an ischemic stroke. Despite thrombolysis, his recurrent neurological symptoms, including dysarthria and cerebellar ataxia, prompted further evaluation. Neuroimaging revealed hyperintense lesions in the right hemi-pons and bilateral middle cerebellar peduncles, raising the possibility of a demyelinating disorder. MOG-IgG seropositivity confirmed the diagnosis of MOG encephalitis. The patient responded well to pulse corticosteroid therapy, followed by maintenance immunosuppression with mycophenolate mofetil, and remained asymptomatic on follow-up. This case underscores the importance of considering autoimmune demyelinating disorders in young patients with recurrent neurological deficits and clinico-radiological dissociation. Early recognition and appropriate immunotherapy can prevent unnecessary thrombolysis and improve patient outcomes. Clinicians should maintain a high index of suspicion for MOGAD as a potential stroke mimic in atypical presentations.

BACKGROUND: X-linked Charcot-Marie-Tooth disease type 1 (CMTX1), caused by pathogenic variants in GJB1 encoding connexin 32, is primarily an inherited peripheral neuropathy. A minority of patients develop transient central nervous system (CNS) dysfunction with reversible white matter lesions, which may mimic acute paediatric stroke. Triggers such as fever, infection and exercise have been reported, but allergy-related exposure has rarely been discussed and causal mechanisms remain uncertain. CASE PRESENTATION: A 9-year-old boy developed acute left-sided weakness, dysarthria and central facial-tongue paresis shortly after pollen exposure. Cranial magnetic resonance imaging (MRI) showed symmetrical diffusion-restricted lesions involving the corpus callosum and bilateral centrum semiovale, with high signal on diffusion-weighted imaging (DWI), corresponding low apparent diffusion coefficient (ADC) values and hyperintensity on T2 fluid-attenuated inversion recovery (FLAIR). Magnetic resonance angiography (MRA), magnetic resonance venography (MRV), cerebrospinal fluid (CSF) studies, autoimmune encephalitis antibodies and oligoclonal bands were unremarkable. Neurological deficits resolved within 12 h. Nerve conduction studies showed mild mixed sensorimotor polyneuropathy with demyelinating features and partial axonal involvement. Serial MRI showed progressive resolution, and diffusion tensor imaging (DTI) demonstrated no obvious displacement, interruption or reduction of major white matter tracts. Whole-exome sequencing and Sanger validation identified a hemizygous GJB1 c.623 A > G (p.Glu208Gly, p.E208G) variant in the proband; his mother was heterozygous and his brother was hemizygous. No recurrent stroke-like episode occurred during 2 years of follow-up, although reduced tendon reflexes persisted. CONCLUSIONS: In children with acute stroke-like episodes and reversible white matter lesions, the coexistence of pes cavus, reduced tendon reflexes or abnormal nerve conduction should prompt evaluation for GJB1-related CMTX1. Pollen exposure was temporally associated with the episode in this patient, but an allergic mechanism remains unproven because allergy-specific biomarkers and cytokines were not obtained during the acute phase.

The hippocampus is increasingly recognised for its role in working memory representations and goal-directed behaviour, yet whether these functions share common neural substrates remains unclear. We investigated short-term memory performance in 27 patients (21 males, 6 females) with LGI1-antibody limbic encephalitis (aLE), a condition with predominant hippocampal involvement, compared to 27 age- and gender-matched healthy controls, using an object-location continuous report task with Bayesian mixture modelling. Patients exhibited predominantly elevated misbinding errors-incorrectly associating objects with non-target locations-with unaltered guessing and only marginally reduced precision. Critically, apathy was positively as sociated with misbinding exclusively in patients, independent of depression and global cognition. Neuroimaging in a subset of patients (n = 12) revealed reduced hippocampal volumes and preliminary evidence for diminished hippocampal-medial prefrontal connectivity, which was associated with both higher apathy and increased misbinding at short retention intervals. These findings demonstrate that hippocampal dysfunction produces convergent deficits in memory binding and motivation, potentially reflecting disruption of a common brain mechanism linking working memory processing to goal-directed behaviour.Significance Statement The hippocampus, a brain region long associated with memory, is increasingly recognised for its role in goal-directed behaviour. We tested patients with autoimmune limbic encephalitis, a condition that primarily damages the hippocampus, on a working memory task that distinguishes different types of errors. Patients showed a predominant impairment in binding object identities to their locations, and these binding errors correlated with apathy-loss of motivation- independent of depression and general cognition. Reduced functional connectivity between the hippocampus and prefrontal cortex was associated with both higher apathy and greater binding errors. Our findings suggest that the hippocampus supports both memory and motivation through common neural mechanisms, with potential clinical implications for cognitive and motivational symptoms in hippocampal disorders.