Taku Fukuda

Acetylcholine receptors loss and postsynaptic damage in MuSK antibody-positive myasthenia gravis

Muscle‐specific tyrosine kinase (MuSK) antibodies are found in some patients with “seronegative” myasthenia gravis (MG), but how they cause myasthenic symptoms is not clear. We visualized acetylcholine receptors (AChRs) and complement component 3 (C3) in muscle biopsies from 10 Japanese MG patients with MuSK antibodies, compared with 42 with AChR antibodies. The AChR density was not significantly decreased in MuSK antibody (Ab)–positive end‐plates compared with AChR antibody–positive end‐plates, and C3 was detected in only two of eight MuSK Ab–positive patients. MuSK antibodies do not appear to cause substantial AChR loss, complement deposition, or morphological damage. Effects on MuSK function need to be explored. Ann Neurol 2005;57:289–293

Reduction of P/Q-type calcium channels in the postmortem cerebellum of paraneoplastic cerebellar degeneration with Lambert-Eaton myasthenic syndrome.

The aim of this study was to clarify whether autoimmunity against P/Q‐type voltage‐gated calcium channels (VGCCs) in the cerebellum was associated with the pathogenesis of paraneoplastic cerebellar degeneration (PCD) with Lambert‐Eaton myasthenic syndrome (LEMS). We used human autopsy cerebellar tissues from three PCD‐LEMS patients and six other disease patients including one with LEMS as the controls. We compared cerebellar P/Q‐type VGCC in these patients and controls for the amount and ratio of autoantibody‐channel complex using an 125I‐ω‐conotoxin MVIIC‐binding assay with Scatchard analysis, and their distribution using autoradiography. The quantity of cerebellar P/Q‐type VGCC measured by Scatchard analysis were reduced in PCD‐LEMS patients (63.0 ± 7.0fmol/mg, n = 3), compared with the controls (297.8 ± 38.9fmol/mg, n = 6). The ratio of autoantibody‐VGCC complexes to total P/Q‐type VGCCs measured by immunoprecipitation assay were increased in PCD‐LEMS patients. We analysed cerebellar specimens by autoradiography using 125I‐ω‐conotoxin MVIIC, which specifically binds to P/Q‐type VGCCs. In PCD‐LEMS cerebellum, the toxin binding sites of P/Q‐type VGCCs were markedly reduced compared with controls, especially in the molecular layer, which is the richest area of P/Q‐type VGCCs in the normal cerebellum. This suggests that P/Q‐type VGCCs of the cerebellar molecular layer is the immunological target in developing PCD‐LEMS.

Seronegative Lambert-Eaton myasthenic syndrome Study of 110 Japanese patients

The authors characterized the clinical and immunologic features of 110 patients with Lambert-Eaton myasthenic syndrome (LEMS). Anti-P/Q-type voltage-gated calcium channels (VGCC) antibodies were detected in 85% of the patients (seropositive) but not in the rest (seronegative). Except for the indication that small cell lung carcinoma is less common in seronegative patients, no significant differences were found in the clinical characteristics of patients who had or did not have anti-P/Q-type VGCC antibodies. The results of passive transfer experiments suggest that seronegative LEMS is also an autoantibody-mediated disorder.

Antibodies against the main immunogenic region of the acetylcholine receptor correlate with disease severity in myasthenia gravis

Objective We developed an assay that detects autoantibodies against the main immunogenic region (MIR) located at the extracellular end of the nicotinic acetylcholine receptor (AChR) α subunit, and investigated its clinical relevance in myasthenia gravis (MG). Methods In this retrospective cohort study, we measured MIR antibody (Ab) titres in sera obtained before treatment and analysed their associations with clinical parameters in 102 MG patients from two neurological centres. MIR Ab titres were determined using a modified competition immunoprecipitation assay in the presence or absence of monoclonal antibody 35. Results 11 of 23 (47.8%) ocular type and 66 of 72 (91.7%) generalised type MG patients were positive for the presence of MIR Abs, defined as a titre >16.8% (3 SDs above the mean for 70 healthy controls). A significantly higher MIR Ab titre (p<0.001) was shown in generalised type (47.9±19.2%) rather than in ocular type MG patients (16.4±8.4%). Bivariate regression analysis using both titre levels of MIR Ab and routine AChR binding Ab as variables revealed MIR Abs to be an exclusive indicator positively associated with disease severity (Myasthenia Gravis Foundation of America classification, p<0.0001; Quantitative MG score, p=0.008), the presence of bulbar symptoms (p<0.0001) and thymoma (p=0.016), and negatively associated with ocular MG (p<0.0001). Conclusions MIR Ab titre levels show much better correlations with factors related to disease severity compared with AChR binding Ab titres. The MIR Ab assay may be useful for predicting MG symptom severity, especially for discriminating between ocular and generalised types of MG.

Thymus histology and concomitant autoimmune diseases in Japanese patients with muscle-specific receptor tyrosine kinase-antibody-positive myasthenia gravis.

The differences in the characteristics of thymus histology, coexisting autoimmune diseases and related autoantibodies between anti‐muscle‐specific receptor tyrosine kinase (MuSK)‐antibody (Ab)‐positive myasthenia gravis (MG) patients, and anti‐acetylcholine receptor (AChR)‐Ab‐positive MG patients are not clearly defined.

Efficacy of prosultiamine treatment in patients with human T lymphotropic virus type I-associated myelopathy/tropical spastic paraparesis: results from an open-label clinical trial

BackgroundHuman T lymphotropic virus type I (HTLV-I)-associated myelopathy/tropical spastic paraparesis (HAM/TSP) is a chronic myelopathy characterized by motor dysfunction of the lower extremities and urinary disturbance. Immunomodulatory treatments are the main strategy for HAM/TSP, but several issues are associated with long-term treatment. We conducted a clinical trial with prosultiamine (which has apoptotic activity against HTLV-I-infected cells) as a novel therapy in HAM/TSP patients.MethodsWe enrolled 24 HAM/TSP patients in this open-label clinical trial. Prosultiamine (300 mg, orally) was administered once daily for 12 weeks. We monitored changes in the motor function of the lower extremities and urinary function as well as copy numbers of the HTLV-I provirus in peripheral blood mononuclear cells (PBMCs).ResultsImprovement in the motor function of the lower extremities based on a reduction in spasticity (for example, decrease in time required for walking and descending a flight of stairs) was observed. In an urodynamic study (UDS), bladder capacity and detrusor pressure and then maximum flow rate increased significantly. Detrusor overactivity and detrusor-sphincter dyssynergia improved in 68.8% and 45.5% of patients observed at pretreatment, respectively. Improvement in UDS corresponded with improvements in the score of nocturia-quality of life questionnaire. HTLV-I proviral copy numbers in PBMCs decreased significantly (approximately 15.4%) compared with pretreatment levels.ConclusionsThese data suggest that prosultiamine can safely improve motor dysfunction of the lower extremities and urinary disturbance as well as reduce HTLV-I provirus levels in peripheral blood. It therefore has potential as a new therapeutic tool for HAM/TSP patients.Trial registrationUniversity Hospital Medical Information Network Clinical Trials Registry (UMIN-CTR) number, UMIN000005969.Please see related commentary: http://www.biomedcentral.com/1741-7015/11/183.

A CLCN1 mutation in dominant myotonia congenita impairs the increment of chloride conductance during repetitive depolarization

Myotonia congenita is caused by mutation of the CLCN1 gene, which encodes the human skeletal muscle chloride channel (ClC-1). The ClC-1 protein is a dimer comprised of two identical subunits each incorporating its own separate pore. However, the precise pathophysiological mechanism underlying the abnormal ClC-1 channel gating in some mutants is not fully understood. We characterized a ClC-1 mutation, Pro-480-Thr (P480T) identified in dominant myotonia congenita, by using whole-cell recording. P480T ClC-1 revealed significantly slowed activation kinetics and a slight depolarizing shift in the voltage-dependence of the channel gating. Wild-type/mutant heterodimers exhibited similar kinetic properties and voltage-dependency to mutant homodimers. Simulating myotonic discharge with the voltage clamp protocol of a 50 Hz train pulse, the increment of chloride conductance was impaired in both wild-type/mutant heterodimers and mutant homodimers, clearly indicating a dominant-negative effect. Our data showed that slow activation gating of P480T ClC-1 impaired the increment of chloride conductance during repetitive depolarization, thereby accentuating the chloride conductance reduction caused by a slight depolarizing shift in the voltage-dependence of the channel gating. This pathophysiology may explain the clinical features of myotonia congenita.

Rheumatoid vasculitis of crural muscles confirmed by muscle biopsy in the absence of inflammatory myopathy: histologic and MRI study

A 60-year-old man who had been diagnosed as rheumatoid arthritis admitted to our hospital by dysesthesia on his legs with edema. Nerve conduction velocity test led to diagnosis of mononeuritis multiplex. Magnetic resonance imaging (MRI) of lower legs showed high intensity in slow tau inversion recovery. Typical vasculitis with neutrophil-dominant cell infiltration was observed by muscle biopsy without inflammatory myopathy or fascitis. Diagnosis was made by rheumatoid vasculitis found in crural muscles. Intravenous cyclophosphamide with oral tacrolimus effectively improved dysesthesia with reduction of inflammatory response.

A case of mixed connective tissue disease complicated with hypertrophic obstructive cardiomyopathy

A 54-year-old female was diagnosed as mixed connective tissue disease (MCTD) complicated with secondary Sjögren’s syndrome. Although she had no dyspnea on exertion, the chest X-ray showed cardiomegaly with interstitial pneumonia. The echocardiogram demonstrated asymmetric hypertrophy of the interventricular septum. Diagnosis of hypertrophic obstructive cardiomyopathy (HOCM) was confirmed by left ventriculography and myocardial biopsy. She was treated with prednisolone, resulting in improvement of swollen hand, elevated muscle enzymes and interstitial pneumonia. A rare complication of HOCM with MCTD was described.

Neurogenic bladder in Lambert–Eaton myasthenic syndrome and its response to 3,4-diaminopyridine

Autonomic dysfunction, as well as neuromuscular involvement, is a common manifestation of Lambert-Eaton myasthenic syndrome (LEMS). Dry mouth and impotence have been described as typical features of autonomic dysfunction, but neurogenic bladder is infrequent or subclinical in LEMS. We report a patient with neurogenic bladder secondary to LEMS whose condition responded to 3,4-diaminopyridine (3,4-DAP). In this patients serum, results of repeated measurement with P/Q-type VGCC antibodies proved positive, but not with N-type VGCC and synaptotagmin antibodies. A review of the literature turned up a few patients with voiding dysfunction related to LEMS, but no urodynamic studies were done on these patients. Ours is the first case in which 3,4-DAP was efficacious in treating LEMS and neurogenic bladder. Responses of 3,4-DAP in urodynamic studies suggest that in this LEMS patient neurogenic bladder was caused by defective neurotransmission both in the autonomic detrusor and skeletal abdominal muscles.