[Muscle-Specific Receptor Tyrosine Kinase Antibody Positive Myasthenia Gravis].

Reportedly, patients with muscle-specific kinase (MuSK) antibody-positive myasthenia gravis (MG) account for approximately 3.0% of all patients with MG in Japan. Compared with patients who have acetylcholine receptor antibody-positive MG, those with MuSK antibody-positive MG show young-onset disease with female predominance, a low rate of ocular involvement (5.9%), and greater severity of dysphagia. The aforementioned types of MG are indistinguishable based on clinical symptoms and electrophysiological tests, and measurement of MuSK antibodies is essential for diagnosis. Thymectomy and complement inhibitors are not indicated for treatment, and acetylcholinesterase inhibitors, steroids, immunosuppressants, plasma exchange, intravenous immunoglobulin therapy, and neonatal Fc receptor inhibitors are used.

[Diagnosis and Treatment of Lambert-Eaton Myasthenic Syndrome].

Approximately 90% of patients with Lambert-Eaton myasthenic syndrome (LEMS) show positive P/Q-type voltage-gated calcium channels antibodies, which can be broadly classified clinically as paraneoplastic, particularly with small cell lung carcinoma and non-paraneoplastic without cancer. The first Japanese guideline for LEMS was developed in May 2022 as MG/LEMS Practice Guideline 2022. This article describes the epidemiology, symptoms, diagnosis, examination, treatment, and prognosis of this condition, based on the LEMS guidelines.

[LEMS: Clinical Significance of Pathogenic Autoantibodies].

Approximately 90% of patients with Lambert-Eaton myasthenic syndrome (LEMS) are positive for P/Q-type voltage-gated calcium channels (VGCCs) antibodies, and can be broadly divided into two groups: paraneoplastic, especially with small cell lung carcinoma and, non-paraneoplastic, without cancer. Under the Japanese LEMS diagnostic criteria 2022, abnormal electrophysiological results is mandatory for diagnosis in addition to muscle weakness. Contrastingly, autoantibodies are useful for diagnosing the etiology and influence treatment strategies. We comprehensively reviewed the MG/LEMS 2022 practice guidelines. Moreover, we presented a case of PCD without LEMS that was positive for P/Q-type VGCCs antibodies_and discussed the clinical significance of the autoantibodies.

Motor end-plate analysis to diagnose immune-mediated myasthenia gravis in seronegative patients.

This study aimed to evaluate the diagnostic usefulness of motor end-plate (MEP) analysis along with clustered acetylcholine receptor (AChR) antibody (Ab) assays in patients with myasthenia-like symptoms but negative routine AChR and muscle-specific kinase (MuSK) Ab tests. MEP analysis of muscle biopsies of the biceps brachii was performed in 20 patients to try to differentiate between those with or without immune-mediated myasthenia gravis (MG). Using a quantitative method, complement C3 deposition and AChR densities in MEPs were examined. Independently, cell-based assays were used to detect serum clustered-AChR Abs. Only five of 20 patients had complement deposition at MEPs; four of these patients had reduced AChR densities similar to those in patients with typical AChR Ab positive MG, and distinct from those in the remaining 15 patients. Two of the four serum samples from these patients had clustered-AChR Abs. All complement-positive patients were considered as having immune-mediated MG and improved with appropriate treatments; although one patient presented with MG 3 years later, the remaining patients had other diagnoses during over 10 years of follow-up. These results suggest the usefulness of MEP analysis of muscle biopsies in diagnosing immune-mediated MG in seronegative patients with myasthenia-like symptoms but, due to the invasiveness of the muscle biopsy procedure, clustered AChR Abs should, if possible, be tested first.

Paraneoplastic Cerebellar Degeneration With P/Q-VGCC vs Yo Autoantibodies.

BACKGROUND AND OBJECTIVES: Paraneoplastic cerebellar degeneration (PCD) is characterized by a widespread loss of Purkinje cells (PCs) and may be associated with autoantibodies against intracellular antigens such as Yo or cell surface neuronal antigens such as the P/Q-type voltage-gated calcium channel (P/Q-VGCC). Although the intracellular location of the target antigen in anti-Yo-PCD supports a T cell-mediated pathology, the immune mechanisms in anti-P/Q-VGCC-PCD remain unclear. In this study, we compare neuropathologic characteristics of PCD with anti-P/Q-VGCC and anti-Yo autoantibodies in an archival autopsy cohort. METHODS: We performed neuropathology, immunohistochemistry, and multiplex immunofluorescence on formalin-fixed and paraffin-embedded brain tissue of 1 anti-P/Q-VGCC, 2 anti-Yo-PCD autopsy cases and controls. RESULTS: Anti-Yo-PCD revealed a diffuse and widespread PC loss together with microglial nodules with pSTAT1+ and CD8+granzymeB+ T cells and neuronal upregulation of major histocompatibility complex (MHC) Class I molecules. Some neurons showed a cytoplasmic immunoglobulin G (IgG) staining. In contrast, PC loss in anti-P/Q-VGCC-PCD was focal and predominantly affected the upper vermis, whereas caudal regions and lateral hemispheres were spared. Inflammation was characterized by scattered CD8+ T cells, single CD20+/CD79a+ B/plasma cells, and an IgG staining of the neuropil in the molecular layer of the cerebellar cortex and neuronal cytoplasms. No complement deposition or MHC-I upregulation was detected. Moreover, synaptophysin was reduced, and neuronal P/Q-VGCC was downregulated. In affected areas, axonal spheroids and the accumulation of amyloid precursor protein and glucose-regulated protein 78 in PCs indicate endoplasmatic reticulum stress and impairment of axonal transport. In both PCD types, calbindin expression was reduced or lost in the remaining PCs. DISCUSSION: Anti-Yo-PCD showed characteristic features of a T cell-mediated pathology, whereas this was not observed in 1 case of anti-P/Q-VGCC-PCD. Our findings support a pathogenic role of anti-P/Q-VGCC autoantibodies in causing neuronal dysfunction, probably due to altered synaptic transmission resulting in calcium dysregulation and subsequent PC death. Because disease progression may lead to irreversible PC loss, anti-P/Q-VGCC-PCD patients could benefit from early oncologic and immunologic therapies.

Two Lambert-Eaton Myasthenic Syndrome Patients with Ameliorated Activities of Daily Living Due to Cholinesterase Inhibitors.

We herein report two P/Q-type voltage-gated calcium channel (VGCC) antibody-positive Lambert-Eaton myasthenic syndrome (LEMS) patients who responded dramatically to cholinesterase inhibitors. Patient 1, a 76-year-old man, had small-cell lung cancer and developed LEMS during chemotherapy. When symptomatic treatment was started with pyridostigmine, gait disturbance was ameliorated, and his modified Rankin scale decreased from 4 points to 3 points. Patient 2, a 68-year-old man, had cancer-free LEMS. Distigmine bromide was very effective and ameliorated not only his gait disturbance but also autonomic symptoms, and his modified Rankin scale decreased from 2 points to 1 point. Cholinesterase inhibitors alone may be effective in a small portion of LEMS patients.

Preoperative risks of post-operative myasthenic crisis (POMC): A meta-analysis.

INTRODUCTION: Myasthenic crisis (MC) is a life-threatening condition in patients with myasthenia gravis (MG), for which thymectomy is known to be a predisposing factor. There are many preoperative factors that have been suggested to increase the occurrence of post-operative myasthenic crisis (POMC), but none have been unanimously concluded as definite risk factors. METHODS: We performed meta-analyses to assess preoperative risk factors for the occurrence of POMC in eligible case-control studies. RESULTS: A total of 10 articles were systematically reviewed and meta-analyses identified preoperative bulbar symptoms, a history of MC, and disease severity (p < .0001), as well as decreased vital capacity (p = .002), as risk factors for POMC. Among the identified risks, the presence of preoperative bulbar symptoms showed the least heterogeneity and was suggested to be the most reliable preoperative risks of POMC. CONCLUSION: Presence of preoperative bulbar symptoms is an easily discernable risk factor for the occurrence of POMC. A history of preoperative MC will further increase the risk of POMC. Patients with these risks require extra caution and should be closely monitored for POMC upon thymectomy.

GRP78 antibodies damage the blood-brain barrier and relate to cerebellar degeneration in Lambert-Eaton myasthenic syndrome.

Lambert-Eaton myasthenic syndrome (LEMS) is an autoimmune disease of the neuromuscular junction caused by autoantibodies binding to P/Q-type voltage-gated calcium channels. Breakdown of the blood-brain barrier and diffusion of cerebellar granule/Purkinje cell-reactive autoantibodies into the CNS are critical for the pathogenesis of paraneoplastic cerebellar degeneration (PCD) with Lambert-Eaton myasthenic syndrome. We recently found evidence that glucose-regulated protein 78 (GRP78) autoantibodies in the plasma of patients with neuromyelitis optica promote the CNS access of AQP4 autoantibodies. In the present study, we investigated whether the GRP78 autoantibodies in PCD-LEMS IgG boost the brain uptake of cerebellar cell-reactive antibodies across the blood-brain barrier and facilitate cerebellar dysfunction. We first evaluated the effects of purified IgG from PCD-LEMS or PCD patients on the blood-brain barrier function in human brain microvascular endothelial cells using a high content imaging system with nuclear factor κB p65 and intracellular adhesion molecule 1 (ICAM1) immunostaining. Next, we identified GRP78 autoantibodies causing blood-brain barrier permeability in PCD-LEMS IgG by co-immunoprecipitation and the living cell-based antibody binding assays. Exposure of brain microvascular endothelial cells to IgG from PCD-LEMS patients induced nuclear factor κB p65 nuclear translocation, ICAM1 upregulation, reduced claudin-5 expression, increased permeability and increased autocrine IL-1ß and IL-8 secretion; the IgG from patients with Lambert-Eaton myasthenic syndrome did not have these effects. We detected GRP78 autoantibodies in the IgG of LEMS-PCD (83.3%, n = 18), but observed fewer in patients with LEMS (6.6%, n = 15) and none were observed in the control subjects (n = 8). The depletion of GRP78 autoantibodies reduced the biological effect of LEMS-PCD IgG on brain microvascular endothelial cells. These findings suggest that GRP78 autoantibodies play a role beyond neuromyelitis optica and that they have direct implications in the phenotypic differences between PCD-LEMS and LEMS.

[Paraneoplastic Cerebellar Degeneration with Lambert-Eaton Myasthenic Syndrome: A Report of an Effectively Treated Case and Systematic Review of Japanese Cases].

A 63-year-old female who developed dizziness, diplopia and subsequent gait disturbance from September X-1 year was analyzed. The first neurological findings in May X year revealed cerebellar ataxia, weakness in the proximal limbs, decreased tendon reflexes, and autonomic symptoms (ADL:mRS 3). Furthermore, an incremental phenomenon was observed in the repetitive nerve stimulation test, and she was diagnosed with Lambert-Eaton myasthenic syndrome (LEMS) based on the serum P/Q-type calcium channel (VGCC) antibody positivity. In addition, small cell lung cancer was detected by chest CT and bronchoscopy, and her cerebellar ataxia was diagnosed as paraneoplastic cerebellar degeneration (PCD). Therefore, the patient underwent chemotherapy and radiotherapy from June in X year. Six months after initiation of treatment, her cerebellar ataxia had almost disappeared and she could walk without assistance (ADL:mRS 1). The P/Q-type VGCC antibodies were also negative at that time. Cases wherein cerebellar ataxia resolved almost completely in parallel with disappearance of the serum P/Q-type VGCC antibodies are of great interest. We conducted a systematic literature review of PCD-LEMS cases in Japan reported since P/Q-type calcium channel antibody measurement was reported in 1995. As a result, 13 cases (including our study) that concurrently displayed cerebellar ataxia and LEMS were selected. The average age of the 13 patients (10 males and 3 females) was 61.5 years. Small cell carcinoma was complicated in 11 patients (10 in the lung and 1 in the oropharynx); in the other 2 patients, cancer was not found at the time of reporting (the observation period was as short as 1-2 months). The time from onset to treatment ranged between 1 week and 10 months. While 1 of the 13 patients developed cerebellar ataxia during the subsequent course of the treatment, the remaining 12 had already developed cerebellar ataxia and LEMS symptoms, although their main neurologic finding was cerebellar ataxia and they were subsequently diagnosed with LEMS after electrophysiological testing and autoantibody detection. Small cell carcinoma was found in 11 patients. We define the pathology following such a certain clinical course as PCD-LEMS. The P/Q-type VGCC antibodies were positive in 11 of the 13 cases, although their antibody titers were not necessarily very high. Treatment for the associated small cell carcinoma might have improved the neurological findings in 9 of the 11 PCD-LEMS patients. The P/Q-type VGCC antibodies were measured before and after the treatment. The PCD-LEMS symptoms improved in all patients and their antibody titers decreased. These findings indicate that P/Q-type VGCC antibodies are involved in the pathology of PCD-LEMS. Appropriate and timely treatment, at least in PCD-LEMS patients in Japan, that actively treats any associated cancer can be expected to improve not only life prognosis but also cerebellar ataxia. (Received October 15, 2018; Accepted November 5, 2018; Published January 1, 2019).

Heterogeneity of auto-antibodies against nAChR in myasthenic serum and their pathogenic roles in experimental autoimmune myasthenia gravis.

Many myasthenia gravis (MG) patients have auto-antibodies against the nicotinic acetylcholine receptor (nAChR), and monoclonal antibodies against the main immunogenic region (MIR) of nAChR can induce experimental autoimmune MG (EAMG). We investigated whether Fab fragment of MIR antibody (Fab35) could block the pathogenicity of polyclonal antibodies. Fab35 partially inhibited nAChR downmodulation, blocked EAMG serum-induced binding of polyclonal antibodies and complement deposition in vitro. Moreover, Fab35 did not ameliorate the EAMG serum-induced EAMG phenotype in rats. These results suggested that the EAMG serum possessed several different pathogenic antibodies that might be sufficient to induce the EAMG phenotype.

[P/Q-type Calcium Channel Antibodies in Lambert-Eaton Myasthenic Syndrome].

Lambert-Eaton myasthenic syndrome (LEMS) is an autoimmune disease of the neuromuscular junction. Approximately 50-60% of patients with LEMS have a tumor, most often small cell lung cancer (SCLC), making LEMS a paraneoplastic neurological syndrome. In Japan, the clinical picture is a male: female ratio of 3:1; mean age, 62 years (17-80 years); and 61% of LEMS patients have SCLC (SCLC-LEMS), with the remainder of patients having no cancer. Patients with LEMS develop a unique set of clinical characteristics, which include proximal muscle weakness, depressed tendon reflexes with post-tetanic potentiation, and autonomic symptoms. Interestingly, less than 10% of patients with LEMS have cerebellar ataxia (LEMS with paraneoplastic cerebellar degeneration). Considering its pathomechanisms, LEMS is a presynaptic disorder of neuromuscular transmission in which quantal release of acetylcholine is impaired by autoantibodies against P/Q-type voltage-gated calcium channels (P/Q-VGCCs) at active zones reducing quantal release of acetylcholine, although an animal model using immunization with purified P/Q-VGCCs has not yet been established. The diagnosis can be confirmed by finding a reduced compound muscle action potential amplitude that increases by over 60% following maximum voluntary activation or 50 Hz nerve stimulation. Approximately 90% of patients who satisfy the above electrophysiological diagnostic criteria are positive for P/Q-VGCC antibodies have their diagnosis confirmed. Specific tumor therapy in SCLC-LEMS will often improve the neurologic deficit. Tumor removal is the primary treatment for LEMS. If primary tumor screening is negative, screening should be repeated after 3-6 months, followed by screening every 6 months until 2 years post diagnosis. Most patients benefit from 3,4-diaminopyridine being administered with pyridostigmine. In those with severe weakness, high-dose intravenous gamma-globulin (IVIg) or plasmapheresis confers short-term benefits. Prednisone, alone or combined with immunosuppressive drugs, can achieve long-term control of the disorder. The results of a prospective cohort study showed that the presence of LEMS with SCLC had a significant survival advantage independent of other prognostic factors including disease extent, age, sex, performance status, and serum sodium values.

Rationale for the clinical guidelines for myasthenia gravis in Japan.

According to the 2014 Japanese clinical guidelines for myasthenia gravis, the most important priority in treatment is maintaining patients' health-related quality of life. Therefore, the initial treatment goal is defined as maintaining a postintervention status of minimal manifestations or better (according to the Myasthenia Gravis Foundation of America classification) with an oral prednisolone dose of 5 mg/day or less. Every effort should be made to attain this level as rapidly as possible. To achieve this goal, the guidelines recommend minimizing the oral prednisolone dose, starting calcineurin inhibitors early in the course of treatment, using intravenous methylprednisolone infusion judiciously (often combined with plasma exchange/plasmapheresis or intravenous immunoglobulin), and effectively treating patients with an early, fast-acting treatment strategy. The early, fast-acting treatment strategy enables more frequent and earlier attainment of the initial goal than other strategies. Thymectomy is considered an option for treating nonthymomatous early-onset myasthenia gravis in patients with antiacetylcholine receptor antibodies and thymic hyperplasia in the early stages of the disease.

Anti-MuSK Antibody-positive Myasthenia Gravis Successfully Treated with Outpatient Periodic Weekly Blood Purification Therapy.

A 37-year-old man with anti-muscle-specific tyrosine kinase (MuSK) antibody-positive myasthenia gravis (MG) presented with subacute progressive dysphagia and muscle weakness of the neck and bilateral upper extremities. Conventional immune-suppressive treatments and high-dose intravenous immunoglobulin were ineffective. He then displayed repeated exacerbations and remissions over the course of two years, despite two to four sessions of plasma exchange (PE) every two months. The patient was successfully treated with outpatient periodic weekly blood purification therapy with alternative PE and double-filtration plasmapheresis using an internal shunt. This case report suggests the benefits of blood purification therapy with an internal shunt against anti-MuSK antibody-positive MG.

CV2/CRMP5-antibody-related Paraneoplastic Optic Neuropathy Associated with Small-cell Lung Cancer.

A 61-year-old woman who had smoked for 41 years developed subacute dizziness, ataxic gait, opsoclonus, and right visual impairment. She had right optic disc swelling and optic nerve gadolinium enhancement on magnetic resonance imaging. She had small-cell lung cancer (SCLC), with CV2/collapsin response mediator protein (CRMP) 5 and HuD antibodies in her serum and cerebrospinal fluid. She was diagnosed with paraneoplastic optic neuropathy (PON) accompanied by paraneoplastic opsoclonus-ataxia syndrome. Her symptoms improved after removing the SCLC. Classical PON is rare in Japan. We recommend assaying for CV2/CRMP5 antibodies and searching for cancer in elderly patients with subacute painless visual impairment.

Paraneoplastic Cerebellar Degeneration and Lambert-Eaton Myasthenic Syndrome Associated with Neuroendocrine Carcinoma of the Oropharynx.

Paraneoplastic cerebellar degeneration and Lambert-Eaton myasthenic syndrome (PCD-LEMS) are usually associated with small-cell lung carcinoma (SCLC). PCD-LEMS with extrapulmonary non-SCLC tumors; however, has not been previously reported. A 78-year-old man presented with dysarthria, dysphagia, staggering gait, and lower extremity muscle fatigue. He was diagnosed with PCD-LEMS associated with neuroendocrine carcinoma of the oropharynx, based on the histological findings of the biopsy, the existence of antibodies against P/Q-type voltage-gated calcium channels, and an incremental response of the compound muscle action potentials during repetitive nerve stimulation tests. Thus, PCD-LEMS should be included in the differential diagnosis of neurological dysfunction, even in extrapulmonary non-SCLC patients.

Analysis of peripheral B cells and autoantibodies against the anti-nicotinic acetylcholine receptor derived from patients with myasthenia gravis using single-cell manipulation tools.

The majority of patients with myasthenia gravis (MG), an organ-specific autoimmune disease, harbor autoantibodies that attack the nicotinic acetylcholine receptor (nAChR-Abs) at the neuromuscular junction of skeletal muscles, resulting in muscle weakness. Single cell manipulation technologies coupled with genetic engineering are very powerful tools to examine T cell and B cell repertoires and the dynamics of adaptive immunity. These tools have been utilized to develop mAbs in parallel with hybridomas, phage display technologies and B-cell immortalization. By applying a single cell technology and novel high-throughput cell-based binding assays, we identified peripheral B cells that produce pathogenic nAChR-Abs in patients with MG. Although anti-nAChR antibodies produced by individual peripheral B cells generally exhibited low binding affinity for the α-subunit of the nAChR and great sequence diversity, a small fraction of these antibodies bound with high affinity to native-structured nAChRs on cell surfaces. B12L, one such Ab isolated here, competed with a rat Ab (mAb35) for binding to the human nAChR and thus considered to recognize the main immunogenic region (MIR). By evaluating the Ab in in vitro cell-based assays and an in vivo rat passive transfer model, B12L was found to act as a pathogenic Ab in rodents and presumably in humans.These findings suggest that B cells in peripheral blood may impact MG pathogenicity. Our methodology can be applied not only to validate pathogenic Abs as molecular target of MG treatment, but also to discover and analyze Ab production systems in other human diseases.

IgG4-related disease with cavernous sinus and intra-orbital lesions diagnosed by nasal mucosa biopsy.

IgG4-related disease is a systemic disease characterized by lesions with IgG4 positive plasma cell infiltration in the involved organs and a raised serum IgG4 level. We report a patient of 70-year-old male presented orbital inflammation of IgG4-related disease. The patient developed right eye pain, double vision, and reduced eye sight. MRI image revealed mild right ocular proptosis and swelling of right carvenous sinus, bilateral intraorbital extraocular muscles and right optic nerve. Right optic nerve showed ring-like enhancement. IgG4-related disease was suspected with increased serum IgG4 level of 355 mg/dl, mediastinal lymphadenopathy and prostate enlargement. Transbronchial lung biopsy and prostate needle biopsy were administered with negative results. The eye related symptoms resolved with time, but serum IgG4 continuously increased. IgG4-related disease was diagnosed by nasal mucosa biopsy, which showed IgG4 positive plasma cells within the inflammatory infiltrate. This report emphasizes the usefulness of nasal mucosa biopsy for the diagnosis of IgG4 related disease with lesions difficult to approach.