Chronic inflammatory demyelinating polyradiculoneuropathy (CIDP) is recognized as a syndrome caused by multiple pathologies. Since the 2010s, it has been clarified that autoantibodies against membranous proteins localized in the nodes of Ranvier and paranodes are positive in subsets of CIDP patients, leading to proposing a new disease concept called autoimmune nodopathies, which is independent of CIDP, in the revised international CIDP guidelines. This article reviews the significance of these autoantibodies, especially anti-neurofascin 155 and anti-contactin 1 antibodies, which have been the most prevalent and achieved a higher degree of consensus.

Cognitive impairment has been reported as a potential sequela of COVID-19. Risk factors associated with this impairment include advanced age, severe infection, and prolonged duration of anosmia (loss of smell). Furthermore, COVID-19 has been reported as a risk factor for Alzheimer disease, and even mild infections have been associated with visuospatial cognitive impairments. While multiple pathophysiological mechanisms have been implicated in COVID-19-related cognitive impairment, persistent infection by the SARS-CoV-2 virus is of particular interest due to its potential implications for treatment. Persistent infection could lead to cognitive impairments through mechanisms such as neurotoxicity mediated by spike proteins, neuroinflammation induced by cytokines, and neuronal cell fusion (syncytia). In terms of treatment, the effectiveness of vaccination has been demonstrated in meta-analyses, and drugs like metformin and antiviral agents hold promise.

An 85-year-old woman was admitted to our hospital with unsteady gait, dizziness, nausea, and vomiting. MRI revealed characteristic abnormal signals in the bilateral cerebellar hemispheres. A brain biopsy was performed which confirmed a definitive histological diagnosis of diffuse glioma. Follow-up MRI showed diffuse abnormal signals that extended from the cerebellum to the brainstem through the cerebellar peduncle without mass formation. Her general condition gradually deteriorated even with the best supportive care, and she died 195 days after admission. Gliomatosis cerebri is characterized by a diffuse infiltrating growth pattern without mass formation in the brain. This case showed a similar proliferation mode from the cerebellum to the brain stem without mass formation. This case was diagnosed based on MRI and pathological findings. Only five similar cases have been previously reported, and compared to these reports, the patient in the present case was the oldest with the poorest prognosis. The histopathological features may influence the appropriate treatment and the prognosis. This disorder is a very rare condition; thus, when we encountered this patient showing cerebellar ataxia with diffuse abnormal MRI signals without mass formation in the cerebellum and brainstem, a brain biopsy was necessary to establish the definitive diagnosis.

Case 1 involved a 68-year-old woman who was admitted to our hospital because of muscle weakness, diffuse subcutaneous edema, dysphagia, and an elevated serum creatine kinase level that had worsened within the previous month. Case 2 involved a 78-year-old woman who was admitted to our hospital because of muscle weakness, bilateral shoulder pain, diffuse subcutaneous edema, and dysphagia that had gradually worsened during the past 5 months. Both patients showed severe diffuse subcutaneous edema and dysphagia and underwent enteral tube feeding. Although they had no skin lesions consistent with dermatomyositis, muscle biopsies showed myxovirus resistance protein A (MxA) expansion, and blood tests showed positivity for anti-nuclear matrix protein 2 (anti-NXP-2) antibody. Therefore, both presents were diagnosed with anti-NXP-2 antibody-positive dermatomyositis sine dermatitis (DMSD). Anti-NXP-2 antibody-positive dermatomyositis has been reported to be closely associated with DMSD, severe edema and dysphagia. Differential diagnosis for patients who develop myositis with severe subcutaneous edema and dysphagia should include anti-NXP-2 antibody-positive dermatomyositis, and it is important to consider measurement of anti-NXP-2 antibody.

The patient is a 44-year-old man. His parents are consanguineous. He experienced muscle weakness in his toe and distal tingling sensation in his feet at 42 years of age, which gradually progressed. Additionally, a marked cyanotic discoloration of the feet appeared and worsened progressively. Neurological examination revealed loss of tendon reflexes and distal muscle weakness in the lower extremities. Findings from nerve conduction studies indicated axonal polyneuropathy. Upon detection of the MME gene mutation, the patient was diagnosed with autosomal-recessive Charcot–Marie–Tooth disease 2T (ARCMT2T). In this case, cyanosis of the lower extremities possibly was associated with ARCMT2T, and it was suggested to be due to neprilysin deletion linked with the MME mutation. This represents the first documented occurrence of cyanosis as a distinctive feature of CMT with MME mutation.

The patient was a 58-year-old Japanese man. At age 52 years, he was diagnosed with human immunodeficiency virus (HIV) infection and had been receiving highly active antiretroviral therapy (HAART). He presented to the emergency department with acute upper left and right lower extremity paralysis. Spinal cord magnetic resonance imaging showed intramedullary signal changes over three vertebral bodies in the cervical spinal cord. Anti-aquaporin-4 antibody was positive in serum, and neuromyelitis optica spectrum disorder (NMOSD) was diagnosed. Steroid pulse therapy and plasma exchange were performed but had limited effects. In Japan, there is no report of NMOSD after HIV infection treated with rituximab. Rituximab administration should be considered in refractory cases of NMOSD after HIV infection.

We present a case of a 54-year-old woman. She was attending our department for thymoma-associated generalized myasthenia gravis. While she was treated with intravenous immunoglobulins for the exacerbation of myasthenic symptoms, she suddenly lost her consciousness for the first time and continued to have mild disorientation along with anterograde and retrograde amnesia afterwards. The symptoms improved after steroid pulse therapy. After searching for autoantibodies, she was diagnosed with anti-VGKC complex antibody-associated limbic encephalitis. As one-third of cases are complicated by thymoma, anti-VGKC complex antibody-positive limbic encephalitis has the aspect of a paraneoplastic neurological syndrome. In this case, masses suspected to be a recurrence of thymoma were found. In cases of thymoma, involvement of anti-VGKC complex antibodies should be considered when central nervous system symptoms appear, and when anti-VGKC complex antibodies are positive, recurrence or exacerbation of thymoma should be considered.

Periodic limb movement disorder (PLMD) is a condition in which patients experience frequent periodic limb movements of sleep (PLMS). Synchronized arousal responses cause sleep fragmentation, resulting in insomnia, daytime sleepiness, and fatigue. A 59-year-old man was identified as having intense sleep-talking and body movements, suggesting rapid eye movement (REM) sleep behavior disorder (RBD). Attended video-polysomnography (PSG) revealed that sleep-talking and body movements occurred only during non-REM sleep and were associated with PLMS-induced arousals (periodic leg movement arousal index, 53.2/h). Pramipexole administration improved events during sleep and daytime sleepiness, and the PSG findings and clinical course led to a diagnosis of PLMD. This case demonstrates that PLMD mimics the symptoms of RBD and that a detailed analysis of monitored video PSG is crucial to confirm the diagnosis of RBD and to identify or exclude other causes of sleep talking and behavior.