Efficacy and Safety of a New Delivery Assist Catheter with a Flexible, Spindle-Shaped Shaft in Mechanical Thrombectomy.

OBJECTIVE: Large-bore aspiration catheters (ACs) are used successfully in mechanical thrombectomy (MT). However, tortuous access routes prevent device navigation because of the ledge effect. The AXS Offset Delivery Assist Catheter is designed to reduce the ledge effect. The purpose of this study was to evaluate whether the Offset affects AC navigation compared with standard inner microcatheters in MT. METHODS: We retrospectively investigated 75 MTs for anterior circulation occlusion between January 2018 and May 2022 at our hospital. All MTs were performed using an AC, and 2 types of inner microcatheter (Offset or 0.021-0.027-inch standard microcatheter) were chosen randomly during AC navigation. The patients' characteristics, MT techniques, angiographic findings, and clinical outcomes were compared between the Offset and standard group (Non-Offset). The puncture to first pass of the lesion time was investigated to compare the characteristics of the inner catheters. RESULTS: The Offset group comprised 12 patients versus 63 in the Non-Offset group. Although most baseline clinical characteristics and outcomes were similar between the groups, the puncture to first pass of the lesion time was significantly shorter in the Offset versus Non-Offset group (31 ± 10 vs. 46 ± 24 minutes, respectively; P = 0.032). In the Offset group, all stent retrievers were deployed via the Offset. One artery dissection and 8 symptomatic intracranial hemorrhages occurred in the Non-Offset group; no complications occurred in the Offset group. CONCLUSIONS: The AXS Offset delivery assist catheter permitted faster and safer navigation of various ACs to the occlusions compared with standard delivery microcatheters in MT.

Analysis of Cerebrovascular Events after Coil Embolization of Unruptured Cerebral Aneurysms in Patients Taking Anticoagulants.

Objective: Antiplatelet therapy is advised to prevent thrombotic complications during endovascular coil embolization of unruptured cerebral aneurysms. Due to multiple antithrombotic treatments, bleeding risk is a concern in patients using oral anticoagulants for existing comorbidities. We investigated the hemorrhagic and ischemic events following endovascular treatment (EVT) of unruptured cerebral aneurysms in patients taking anticoagulation and antiplatelet therapy. Methods: Between March 2013 and February 2019, 262 patients undergoing EVT for unruptured cerebral aneurysms and having at least 6 months of postoperative follow-up data were included in this retrospective study. Patients taking oral anticoagulants and antiplatelet drugs for cerebral vascular events following EVT were compared with those taking only antiplatelet agents. Results: Of the 262 patients, 12 (4.6%) used anticoagulants before EVT for a preexisting condition. Cerebrovascular events after coil embolization were observed in 3 patients taking both anticoagulant and antiplatelet drugs and in 14 patients taking only antiplatelet drugs (25% vs. 5.6%, respectively, p = 0.035). Vitamin K antagonist (VKA) was administered in five patients and direct oral anticoagulants (DOACs) in seven patients. Patients taking VKA experienced cerebrovascular events, whereas those taking DOACs did not (p = 0.045). Conclusion: Our study showed that patients using oral anticoagulants and antiplatelet drugs experienced more cerebrovascular events after EVT for unruptured cerebral aneurysms. These results suggest that in patients requiring oral anticoagulants, DOACs may be more beneficial than VKA for preventing stroke occurrences after EVT.

HTLV-1-associated demyelinating neuropathy: A case report and review of the literature.

A 78-year-old man developed paresthesias in the extremities. He was referred to our hospital because of positive anti-human T-cell leukemia virus type 1 (HTLV-1) antibodies in the serum and the presence of abnormal lymphocytes. He was diagnosed as chronic-type adult T-cell leukemia/lymphoma. Neurological examination revealed sensory impairment in the distal parts of the extremities with loss of deep tendon reflexes. Nerve conduction study showed motor and sensory demyelinating polyneuropathy, indicating a diagnosis of HTLV-1-associated demyelinating neuropathy. Corticosteroid therapy followed by intravenous immunoglobulin therapy improved his symptoms. Since demyelinating neuropathy associated with HTLV-1 infection is not well recognized, we here report its characteristics and clinical course through our case report and literature review.

[Carotid artery stenting using cerebral angiography 3D fusion imaging without contrast agent: a case report].

A 79-year-old-man with a clinical history of type 2 diabetes and hypertension was admitted to our hospital for recurrent right hemiparesis. He was referred to our department with left internal carotid artery stenosis. Cerebral angiography with a slight contrast agent revealed NASCET 86% stenosis at the left internal carotid bifurcation. Although no neurological deficit was observed, he had a renal dysfunction with an estimated glomerular filtration rate of 32.2 ml/min/1.73 m2. We used a 3D fusion image obtained from the initial angiography with B-mode and intravascular ultrasound to avoid aggravating renal function instead of using a contrast medium. Following the procedure, favorable expansion of the stenotic region was achieved, and no evidence of recurrence was seen during the follow-up period. 3D fusion imaging is a valuable and safe method for endovascular treatment of carotid artery stenosis for patients with renal dysfunction.

Eosinophilic Granulomatosis with Polyangiitis Presenting with Myocarditis as an Initial Symptom: A Case Report and Review of the Literature.

A 66-year-old woman with a history of bronchial asthma had shortness of breath and fatigue upon mild exercise. She was diagnosed as congestive heart failure. A blood test showed eosinophilia without the presence of anti-neutrophil cytoplasmic antibody (ANCA), and a myocardial biopsy specimen revealed eosinophilic infiltration in the myocardium. Eosinophilia was improved when she was administered short-term methylprednisolone. After that, she had numbness and pain in her lower limbs with re-elevation of eosinophils. She had dysesthesia and hypalgesia in the distal part of the limbs. Sural nerve biopsy revealed axonal degeneration and thickness of the arterial wall, indicating a diagnosis of eosinophilic granulomatosis with polyangiitis (EGPA). Two courses of steroid pulse therapy were performed, resulting in marked improvement of her sensory symptoms. ANCA-negative EGPA might be associated with myocarditis and peripheral neuropathy. A sufficient immunotherapy should have been considered to prevent rapid progression.

Clinical features of Barré-Lièou syndrome and efficacy of trazodone for its treatment: A retrospective single center study.

Barré-Lièou syndrome (BLS) is a manifestation of various autonomic and secondary symptoms including muscle stiffness, tinnitus, dizziness, and pain in various body parts. Although considered to be caused by hyperactivation of the autonomic nervous system due to trauma, there is currently no firmly established etiology or evidence on the treatment and clinical features of BLS. We retrospectively examined the clinical features of BLS and evaluated the efficacy of trazodone (TZD) for its treatment. We conducted a retrospective analysis of the data of 20 consecutive cases with suspected BLS who were treated in our hospital between 2016 and 2019. BLS symptoms were rated on a 10-point scale, and two groups were defined, that is, a mild-BLS group (BLS scores, 1-5) and a severe-BLS group (BLS scores, 6-10). Univariate analysis of patient factors was performed. The BLS score was 6.0 ± 1.7, and the maximum TZD dose was 80 ± 34 mg/day; nine patients (45%) were TZD free, and no TZD side effects were observed, while all patients had a good clinical outcome. There were significant differences between the mild-BLS and severe-BLS groups in the period from injury to diagnosis (p = 0.015), chest/back pain (p < 0.001), constipation (p = 0.001), and maximum TZD dose (p = 0.008). BLS involves posttraumatic autonomic symptoms accompanied by depression and insomnia. The sympathetic hypersensitivity theory could explain its etiology. TZD could effectively and safely treat BLS, and early diagnosis and treatment can contribute toward good clinical outcomes. Enhanced recognition and understanding of this disease are warranted.

Types of intraparenchymal hematoma as a predictor after revascularization in patients with anterior circulation acute ischemic stroke.

BACKGROUND: Intracranial hemorrhage after revascularization for acute ischemic stroke is associated with poor outcomes. Few reports have examined the relationship between parenchymal hematoma after revascularization and clinical outcomes. This retrospective study aimed to investigate the risk factors and clinical outcomes of parenchymal hematoma after revascularization for acute ischemic stroke. METHODS: Ninety-three patients underwent revascularization for anterior circulation acute ischemic stroke. Patient characteristics and clinical outcomes were compared between patients with and without post procedural parenchymal hematoma using the following parameters: age, sex, occlusion location, presence of atrial fibrillation, diffusion-weighted imaging-Alberta stroke program early computed tomography score (DWI-ASPECTS), National Institute of Health Stroke Scale (NIHSS) score, recombinant tissue plasminogen activator, thrombolysis in cerebral infarction > 2b, door-to-puncture time, onset-to-recanalization time, number of passes, and modified Rankin Scale scores. RESULTS: Parenchymal hematomas were not significantly correlated with age, sex, occlusion location, atrial fibrillation, DWI-ASPECTS, NIHSS score, recombinant tissue plasminogen activator, thrombolysis in cerebral infarction > 2b, door-to-puncture time, onset-to-recanalization time, and number of passes, but were significantly correlated with poor clinical outcomes (P = 0.001) and absence of the anterior communicating artery evaluated using pre procedural time-of-flight magnetic resonance angiography (P = 0.03). CONCLUSION: Parenchymal hematoma was a predictor of poor outcomes. In particular, the absence of the anterior communicating artery on pre procedural time-of-flight magnetic resonance angiography is a potential risk factor for parenchymal hematoma after revascularization for anterior circulation acute ischemic stroke.

[A Case of Paraneoplastic Opsoclonus and Ataxia Appeared at Progression of Prostate Cancer].

An 80-year-old man was diagnosed with prostate cancer in April 2014 and underwent anticancer treatment. His serum prostate-specific antigen (PSA) level was abruptly increased on December 26, 2014. He was admitted to the neurological department of our hospital on January 14, 2015, because of the appearance of staggering gait and diplopia. Neurological examination revealed marked opsoclonus, limb ataxia and ataxic gait. The patient was diagnosed with paraneoplastic opsoclonus and ataxia caused by prostate cancer relapse. Steroid pulse therapy was initiated and his symptoms, including opsoclonus and ataxia, markedly improved. Although most cases of paraneoplastic opsoclonus precede the discovery of cancer, our case developed symptoms simultaneously with relapse and acute progression of prostate cancer. Paraneoplastic opsoclonus with prostate cancer is rare. Additionally, our case showed excellent response of opsoclonus to steroid therapy without treatment of the underlying disease. (Received June 1, 2020; Accepted September 18, 2020; Published February 1, 2021).

[A Case of Immune-Mediated Necrotizing Myopathy Associated with Primary Sjögren Syndrome].

A 66-year-old woman visited our hospital complaining of shortness of breath during exertion and progressive weakness in all her limb muscles. On admission, we noted muscle weakness in her trunk and in her proximal limb muscles, although, her muscle MRI showed no remarkable findings. However, her serum CK level (2,747U/L) was above the normal range. Histopathological examination of muscle biopsy, performed from the left biceps brachii muscle, revealed immune-mediated necrotizing myopathy (IMNM). Her serum samples were negative for myositis-associated autoantibodies (MAAs), anti-SRP, and HMGCR antibodies. However, as the anti-SS-A antibody level in her serum was high (53.2U/mL), we conducted the salivary gland biopsy and the Schirmer test on her eyes. We found lymphocytes infiltration in her salivary gland tissue, and thus, she was diagnosed with primary Sjögren syndrome (SjS). We also observed necrotizing myopathy associated with the SjS. Following her treatment with oral steroids, her symptoms and CK level improved. Although, inflammatory myositis frequently occurs in association with general collagen diseases, necrotizing myopathy has rarely been observed secondary to SjS. We report here this rare case study along with the review of the relevant literature. (Received June 24, 2020; Accepted October 12, 2020; Published February 1, 2021).

Isolated Cerebral Vasculitis in the Unilateral Middle Cerebral Artery in a Case with SLE.

A 47-year-old woman, who was diagnosed to have systemic lupus erythematosus (SLE), was admitted because she suffered a severe ischemic stroke three weeks after experiencing a transient attack of aphasia. Diffusion-weighted MRI revealed high intensity at the borderzone of the middle cerebral artery (MCA), while the proximal portion of the left MCA was occluded with its vascular wall enhanced by gadolinium. Intravenous methylprednisolone and heparin were administrated without any symptomatic benefit. She developed severe right hemiparesis with aphasia. Isolated cerebral vasculitis in the large vessel has been rarely reported in SLE patients. The presence of an enhanced vascular wall in the MRI with gadolinium could support the diagnosis.

Myasthenia Gravis with Anti-Muscle-Specific Tyrosine Kinase Antibody during Pregnancy and Risk of Neonatal Myasthenia Gravis: A Case Report and Review of the Literature.

A 31-year-old woman presented with a nasal voice, dysarthria, and upper limb weakness during her first pregnancy. Soon after delivery of her first baby, her symptoms disappeared. At the age of 34 years, during her second pregnancy, her nasal voice re-appeared. After delivery of the second baby, her nasal voice worsened, and bilateral eyelid ptosis and easy fatigability were also evident. She was referred to our hospital. Because of her myasthenic symptoms and anti-muscle-specific tyrosine kinase (MuSK) antibody (Ab)-positive status, she was diagnosed as having myasthenia gravis (MG). Her symptoms were worse than those in her first pregnancy. She was treated with oral steroid and double filtration plasmapheresis. After initiation of treatment, her myasthenic symptoms improved completely. In addition, her baby developed transient neonatal MG (TNMG) on the fourth day after birth and then gradually recovered over 30 days. It should be noted that symptoms of patients with anti-MuSK Ab-positive MG (MuSK-MG) can deteriorate during pregnancy, and the babies delivered of patients with MuSK-MG have a high probability of developing TNMG.

Sensitivity and specificity of cardiac 123I-MIBG scintigraphy for diagnosis of early-phase Parkinson's disease.

INTRODUCTION: The purpose of this study was to investigate the diagnostic accuracy of cardiac 123I-metaiodobenzylguanidine (MIBG) scintigraphy for the diagnosis of Parkinson's disease (PD), especially in the early stages. METHODS: We investigated 600 patients who underwent cardiac 123I-MIBG scintigraphy to diagnose their parkinsonism and/or cognitive impairment. Of 600 research subjects, 272 patients were clinically diagnosed with PD. MIBG uptake was compared between patients with PD and other diseases. Furthermore, the sensitivity and specificity of cardiac 123I-MIBG scintigraphy to diagnose PD was estimated by disease duration (<3 years: early group vs. over 3 years: late group). We also assessed the relationship between MIBG uptake and Hoehn & Yahr stage. RESULTS: MIBG uptakes of PD patients were significantly decreased compared with those of other diseases except dementia with Lewy bodies and pure autonomic failure (p < .05 for all). In the early group, the sensitivity and specificity of the delayed heart to mediastinum (H/M) ratio were 68.7% and 91.7%, respectively, while in the late group, the sensitivity was 86.3% and the specificity was 74.0%. In addition, the early and delayed H/M ratios were decreased with higher Hoehn & Yahr stages in PD patients. CONCLUSION: Our findings demonstrated that cardiac 123I-MIBG scintigraphy had sufficient diagnostic accuracy to detect the early phase of PD. Indeed, this study of a large number of patients provides further external validation that MIBG has diagnostic ability to distinguish PD from atypical parkinsonism.

Cerebrospinal Fluid CXCL10 as a Candidate Surrogate Marker for HTLV-1-Associated Myelopathy/Tropical Spastic Paraparesis.

Human T-cell leukemia virus type 1 (HTLV-1)-associated myelopathy/tropical spastic paraparesis (HAM/TSP) is a debilitating, progressive disease without effective treatment; therefore, development of disease modifying therapy that improves long-term functional outcomes is an unmet need for patients. However, it is virtually impossible to consider this as a primary endpoint in clinical trials owing to the prolonged disease course. Therefore, development of surrogate markers that help predict the effectiveness of new interventions is essential. Currently, several candidate surrogate markers have been identified for HAM/TSP. Cerebrospinal fluid (CSF) C-X-C motif chemokine 10 (CXCL10) is involved in the pathogenesis of HAM/TSP and was shown to correlate with disease progression. However, it remains unclear whether changes in CSF CXCL10 levels are observed in response to treatment and whether these correlate with prognosis. Here we investigated several markers, including CSF CXCL10, in this respect. Data pertaining to patient characteristics and results of motor function evaluation and CSF examination of 13 HAM/TSP patients who received steroid treatment were retrospectively analyzed. Osame motor disability scores (OMDS), 10 m walking time, and CSF levels of CXCL10, neopterin, total protein, cell counts, and anti-HTLV-1 antibody titer were compared before and after steroid therapy. Levels of all CSF markers, with the exception of cell count, were significantly decreased after treatment. Nine of the 13 patients (69.2%) showed improvement in OMDS and were considered responders. Pre-treatment CSF levels of CXCL10 and anti-HTLV-1 antibody titer in responders were higher than those in non-responders (p = 0.020 and p = 0.045, respectively). Patients who continued low-dose oral prednisolone maintenance therapy after methylprednisolone pulse therapy showed sustained improvement in OMDS and CSF CXCL10 and neopterin levels lasting for 2 years. In contrast, OMDS and the CSF marker levels in patients who discontinued treatment returned to pre-treatment levels. This rebound phenomenon was also observed in patients who discontinued oral prednisolone therapy independently of pulse therapy. Our findings suggest that CSF CXCL10 may serve as a therapy-response and therapy-predictive marker for HAM/TSP. In addition, since decrease in CSF CXCL10 level was associated with good functional prognosis, CSF CXCL10 is a potential surrogate marker for treatment of HAM/TSP.

A case of drug-induced hypersensitivity syndrome induced by salazosulfapyridine combined with SIADH caused by interstitial pneumonia.

We present a case of a patient with drug-induced hypersensitivity syndrome (DIHS) caused by salazosulfapyridine combined with syndrome of inappropriate secretion of antidiuretic hormone (SIADH) caused by interstitial pneumonia (IP). A 67-year-old man with a past history of rheumatism (RA) presented with right hemiparalysis and aphasia as the chief complaints. A diagnosis of left embolic cerebral infarction following trial therapy for RA based on computed tomography findings was made, and external decompression was performed. Salazosulfapyridine was newly started on day 7. Dabigatran was started on day 37. On day 41, the patient developed fever. On day 42, edema and erythema appeared on his face, and erythema and rash appeared on his trunk and extremities, with gradual transition to erythroderma. The drug eruption was initially attributed to the dabigatran. Various symptoms of organ dysfunction (enteritis, myocarditis, interstitial pneumonia, hepatic disorder, stomatitis, and others) then appeared and persisted; hence, a diagnosis of DIHS associated with human herpes virus 6 and cytomegalovirus infection induced by salazosulfapyridine was suggested, and the oral administration of salazosulfapyridine was discontinued on day 53. Hyponatremia was observed in association with exacerbation of IP. Due to low serum osmotic pressure and prompt improvement of the serum sodium level by fluid restriction, the SIADH was attributed to IP. In this case, steroid pulse therapy followed by gradual decrease therapy prevented worsening of the condition.

Juvenile Muscular Atrophy of the Proximal Upper Extremity as So-Called Proximal-Type Hirayama Disease: Case Report and Review of the Literature.

Hirayama disease is a distinct type of cervical myelopathy characterized by juvenile onset of unilateral muscular atrophy of a distal upper extremity. We report herein a case with Hirayama disease-like juvenile muscular atrophy involving proximal muscles in the upper extremities. In this case, in the flexion position of the neck, cervical magnetic resonance imaging revealed that the spinal cord was compressed by expansion of the posterior extradural space with forward displacement of the dura matter. These neuroimaging results are identical to those of Hirayama disease. However, the involved muscles in this case were the proximal muscles, unlike Hirayama disease. Five previous cases have displayed this rare subtype of Hirayama disease. The cause of the unique phenotype may be abnormal cervical column alignment, with upper cervical kyphosis producing a higher apex of the vertebral level in a cervical flexion position, resulting in mid-cervical segmental myelopathy.

Pituitary metastasis of breast cancer mimicking IgG4-related hypophysitis.

IgG4-related hypophysitis, which is the pituitary gland inflammation caused by IgG4 positive lymphocytes, can affect cavernous sinus and orbital apex leading to developing cranial nerve related symptoms such as orbital apex syndrome (OAS). Here we report a case of hypopituitarism associated with OAS caused by pituitary metastasis of the breast cancer with elevated serum IgG4 level, who initially resembled to IgG4-related hypophysitis. Although this case had some features in common with igG4-related hypophysitis. The symptoms and pituitary enlargement were typical. However, steroid treatment did not improve her symptoms. Thus, we performed a tissue biopsy. Histopathologic examination of the hypophyseal tumor confirmed metastatic breast cancer in her pituitary. Pituitary metastatic tumor should be suspected if a case with OAS was once diagnosed as a cancer.

Fasciculation intensity and disease progression in amyotrophic lateral sclerosis.

OBJECTIVE: To investigate the association between the frequency and intensity of fasciculations with clinical measures of disease progression in amyotrophic lateral sclerosis (ALS). METHODS: Twenty-four consecutive patients with ALS underwent clinical review and neuromuscular ultrasound assessment to detect intensity of fasciculations. Results were correlated with clinical markers of disease severity, as measured by the ALS Functional Rating Scale-revised (ALSFRS-R) and rate of disease progression (ΔFS), in addition to assessment of cortical motor function. RESULTS: Disease duration negatively correlated (R = -0.530, p < 0.01) with fasciculation intensity, while the ΔFS positively correlated with the fasciculation number (R = 0.626, p < 0.01). In terms of potential central contributions to ectopic impulse generation, patients were classified into cohorts based on their fasciculation intensity and short interval intracortical inhibition (SICI). ΔFS was significantly higher in patients with established hyperexcitability (low SICI) with high fasciculation intensity compared to those patients with minimal SICI change. CONCLUSIONS: Fasciculation intensity appears linked to disease progression and separately to markers of cortical dysfunction, specifically the advent of cortical hyperexcitability. SIGNIFICANCE: Assessment of the intensity of patient fasciculations is a noninvasive approach that may provide further insight disease pathophysiology in ALS.

Implications of structural and functional brain changes in amyotrophic lateral sclerosis.

INTRODUCTION: Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease that causes progressive muscle weakness and disability, eventually leading to death. Heterogeneity of disease has become a major barrier to understanding key clinical questions such as prognosis and disease spread, and has disadvantaged clinical trials in search of therapeutic intervention. Patterns of disease have been explored through recent advances in neuroimaging, elucidating structural, molecular and functional changes. Unique brain signatures have emerged that have lent a greater understanding of critical disease mechanisms, offering opportunities to improve diagnosis, guide prognosis, and establish candidate biomarkers to direct future therapeutic strategies. Areas covered: This review explores patterns of cortical and subcortical change in ALS through advanced neuroimaging techniques and discusses the implications of these findings. Expert commentary: Cortical and subcortical signatures and patterns of atrophy are now consistently recognised, providing important pathophysiological insight into this heterogenous disease. The spread of cortical change, particularly involving frontotemporal networks, correlates with cognitive impairment and poorer prognosis. Cortical differences are also evident between ALS phenotypes and genotypes, which may partly explain the heterogeneity of prognosis. Ultimately, multimodal approaches with larger cohorts will be needed to provide sensitive biomarkers of disease spread at the level of the individual patient.

Multiple Thrombi in the Heart in Trousseau Syndrome Caused by Pancreatic Carcinoma.

A 65-year-old woman presented to our emergency room because of sudden onset of right hemiparesis with severe fatigue. Neurological examination revealed right hemiparesis with right facial numbness and an extensor planter response on the right side.Magnetic resonance imaging with diffusion-weighted imaging revealed multiple highintensity areas in both cerebral hemispheres and the right cerebellum. A diagnosis of acute stage of multiple brain infarctions caused by emboli was made. An abdominal computed tomography showed a pancreatic tumor with multiple liver metastases. High D-dimer and serum carbohydrate antigen 19-9 concentration strongly suggested Trousseau syndrome associated with pancreatic cancer. The patient had another large embolic stroke and died on day 47. Autopsy was performed. There were large thrombi in the left ventricular apex and in the left atrial appendage There was also a papillary-shaped vegetation on the aortic valve that consisted mainly of fibrin without any inflammatory cells or destruction of the valve, these findings being characteristic of NBTE. This case is remarkable in that the patient had 3 different types of cardiac thrombi in her heart associated with Trousseau syndrome.

Skeletal Muscle Involvement in Antisynthetase Syndrome.

Importance: Antisynthetase syndrome, characterized by myositis, interstitial lung disease, skin rash, arthropathy, and Raynaud phenomenon, is a clinical entity based on the presence of aminoacyl transfer RNA synthetase (ARS) antibodies in patients' serum. However, antisynthetase syndrome is not included in the histological subsets of idiopathic inflammatory myopathies. Objective: To elucidate the clinical features of myositis in patients with antisynthetase syndrome. Design, Setting, and Participants: In this cohort study, muscle biopsy and blood samples were collected from 460 patients with idiopathic inflammatory myositis from various regional referral centers throughout Japan between October 2010 and December 2014. Data were analyzed in March 2016. Exposures: Six different anti-ARS antibodies were detected in serum by RNA immunoprecipitation. Line blot assay and protein immunoprecipitation were also performed. HLA-DRB1 alleles were genotyped. Main Outcomes and Measures: The main outcomes were muscle manifestations and histological findings. Predisposing factors, extramuscular symptoms, and follow-up information were also studied. Results: Of 460 patients with idiopathic inflammatory myopathies, 51 (11.1%) had anti-ARS antibodies. Of this subset, 31 (61%) were women, with a mean (SD) age at disease onset of 60.2 (16.1) years. Among 6 different anti-ARS antibodies, only 1-the anti-OJ antibody-was not detected by line blot assay but by RNA immunoprecipitation. There were no significant HLA-DRB1 alleles associated with anti-ARS antibodies. All 51 patients presented with muscle limb weakness; 14 (27%) had severe limb weakness, 17 (33%) had neck muscle weakness, 15 (29%) had dysphagia, and 15 (29%) had muscle atrophy. Although patients with anti-OJ antibodies showed severe muscle weakness, the clinical presentations of antisynthetase syndrome were relatively homogeneous. In histology, perifascicular necrosis, the characteristic finding of antisynthetase syndrome, was found in 24 patients (47%). Myositis with anti-ARS antibodies responded to the combination of immunosuppressive therapy with favorable outcomes. Interstitial lung disease, found in 41 patients (80%), was more closely associated with mortality than myositis. Conclusions and Relevance: Although clinical presentations of antisynthetase syndrome were relatively homogeneous, anti-OJ antibodies were associated with severe muscle involvement. Antisynthetase syndrome is a clinical and histological subset among idiopathic inflammatory myopathies.