Thrombotic microangiopathy in a patient with anti-signal recognition particle antibody-positive immune-mediated necrotizing myopathy

We describe the case of a 61-year-old woman with anti-signal recognition particle (SRP) antibody-positive immune-mediated necrotizing myopathy (IMNM) who exhibited biopsy-confirmed thrombotic microangiopathy (TMA). The patient developed proximal-dominant muscle weakness and was diagnosed with anti-SRP antibody-positive IMNM based on muscle biopsy results and serological examination. A high-dose corticosteroid prescription was initiated, followed by intravenous methylprednisolone and intravenous immunoglobulin therapy (IVIg). The patient showed IVIg-induced hemolytic anemia with preserved ADAMTS13 activity. Transient oral tacrolimus administration was initiated. Approximately 8 weeks after admission, the serum creatinine levels gradually increased. Renal histological examination revealed TMA, including ischemic changes in the renal tubules, stenosis, and occlusion of the interlobular arteries with fibrinoid necrosis of the afferent arteriolar walls. The arteriolar walls demonstrated an accumulation of C1q and C3c. Myofiber damage in patients with IMNM accounts for the activation of the classical pathway of the complement cascade in the sarcolemma due to antibody deposition. Additionally, a membrane attack complex is observed on capillaries in the muscle tissues of patients with anti-SRP antibody-positive IMNM. Although drug-induced pathomechanisms, such as IVIg and tacrolimus, can trigger the development of TMA, we suggest that the presence of serum anti-SRP antibodies would be implicated in complement-associated kidney vascular damage.

Corrigendum: Characteristics of cardiac involvement in immune-mediated necrotizing myopathy

[This corrects the article DOI: 10.3389/fimmu.2023.1094611.].

Characteristics of cardiac involvement in immune-mediated necrotizing myopathy

Objective

To investigate the characteristics of cardiac involvement due to Immune-mediated Necrotizing Myopathy (IMNM).

Methods

Patients diagnosed with Immune-mediated Necrotizing Myopathy (IMNM) who attended the Department of Neurology and the Department of Rheumatology and Immunology at the First Medical Center of the PLA General Hospital between February 2011 and June 2022 were collected. Clinicopathological diagnosis of IMNM was performed according to the criteria established by the European Neuromuscular Center (ENMC). All patients underwent muscle biopsy and Myositis-specific antibodies (MSAs) testing. Information included age, gender, disease duration, intramuscular and extramuscular manifestations, laboratory findings (including creatine kinase, lactate dehydrogenase levels, troponin T, myoglobin and atrial natriuretic peptide), electromyography, skeletal muscle pathology and immunohistochemical staining.

Results

A total of 57 patients were included in this study. Of the serological tests, 56.1% (32/57) were positive for SRP, 21.1% (12/57) were positive for HMGCR and 22.8% (13/57) were seronegative. Thirty patients (52.6%, 30/57) presented with varying degrees of cardiac involvement. We performed ECG in 23 patients and found 6 patients with arrhythmia (26.1%), 12 patients with myocardial ischemia (52.2%), and 7 patients with acute coronary syndrome (ST elevation and non-ST elevation myocardial infarction) (30.4%), and 4 patients with left axis deviation or left ventricular high voltage, suggesting left ventricular hypertrophy (17.4%). Cardiac ultrasound was performed in 14 patients and 3 showed pericardial effusion (21.4%); Decreased left ventricular ejection fraction and atrial enlargement were 2 each; 8 showed a decrease in left ventricular diastolic function (57.1%). In addition, one patient had myocardial edema.

Conclusion

Cardiac involvement is not uncommon in IMNM. However, besides clearly statistically significant differences in the disease course, and in the values of troponin T and myoglobin, our data did not show any statistically significant difference in other features of cardiac involvement between patients with different subtypes of IMNM.

COVID-19 Pneumonia Followed by Anti-signal Recognition Particle Antibody-positive Fibrosing Interstitial Lung Disease: A Case Report

Coronavirus disease 2019 (COVID-19) pneumonia is caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and is frequently accompanied by various sequelae. Interstitial lung diseases (ILDs) are observed in COVID-19 pneumonia patients after recovery, probably due to persistent inflammation in the lungs. We herein report a case of ILD with anti-signal recognition particle antibodies following severe COVID-19 pneumonia. The patient was diagnosed with ILD three months after COVID-19 pneumonia. Although the exact mechanism is unknown, the autoantibody-induced immune response might have been the pulmonary fibrosis trigger in this patient.

Plasma exchange therapy in refractory inflammatory myopathy with anti-signal recognition particle antibody: a case series

OBJECTIVES

To explore the efficacy of plasma exchange (PE) therapy in refractory idiopathic inflammatory myopathy (IIM) patients with positive anti-signal recognition particle (SRP) antibody.

METHODS

Nine refractory IIM patients with positive anti-SRP antibody were enrolled, who received PE therapy at Ruijin Hospital from Octobor 2017 to December 2020. The clinical manifestations, laboratory tests, chest CT and lower extremity MRI images before and after PE therapy were compared. The treatment response was evaluated by the 2016 American College of Rheumatology (ACR)/European League Against Rheumatism (EULAR) myositis response criteria.

RESULTS

88.9% (8/9) subjects had achieved improvement by 3 weeks after PE therapy, with 55.6% (5/9) minimal improvement and 33.3% (3/9) moderate improvement. There were statistically significant improvements between baseline and after PE therapy at 3 weeks on the core set measures: physician global activity, patient global activity, Health Assessment Questionnaire (HAQ), manual muscle testing (MMT), extramuscular disease activity, and muscle enzymes activity including creatine kinase (CK), lactate dehydrogenase (LDH), aspartate transaminase (AST), except for alanine transaminase (ALT). Moreover, the chest CT showed regression of ground glass opacities and irregular linear opacities after PE therapy in four patients with interstitial lung disease. The MRI images of lower extremity in four patients showed reduction of muscle oedema after the therapy.

CONCLUSION

PE therapy is effective for refractory IIM patients with positive anti-SRP antibody. It should be considered as an alternative treatment for those patients who are resistant to the combined therapy of glucocorticoids and immunosuppressive agents.

Refractory Myositis Affecting the Intrinsic Muscles of the Hand

Myositis generally affects the proximal muscles. However, we herein report a case of a 48-year-old woman with intractable myositis affecting the intrinsic muscles of the hands. Her myositis, which developed in childhood, was refractory to treatment with steroids and several immunosuppressants, causing walking disability. After experiencing pain and swelling in the hands for six months, she was diagnosed with myositis of the intrinsic muscles of the hands and tested positive for the anti-signal recognition particle antibody. Intravenous immunoglobulin therapy improved the myositis of the hands. This case suggests that inflammation caused by intractable myositis can extend to the hands.

Difficult case: rituximab in anti-SRP antibody myositis in pregnancy

A 30-year-old nulliparous woman presented at 15-week gestation with severe skeletal and respiratory muscle weakness, having been diagnosed with anti-signal recognition particle antibody myositis 3 years before. Remission had previously been induced with rituximab (after failure of standard therapies). She had continued oral prednisolone and rituximab every 6 months but had stopped this when planning pregnancy. At 16-weeks gestation, she restarted corticosteroids and rituximab, with clinical and biochemical recovery and no complications. Rituximab should ideally be given in the first trimester; treatment later in pregnancy increases the risk of neonatal B-cell depletion and cytopenias. The fetal risk from drug therapy must be weighed against the risk to mother and fetus from untreated disease. This report highlights the importance of preconception counselling for disease control and patient education regarding medication safety and early referral to obstetric medicine clinics, to facilitate complex clinical decision-making.

Development of Necrotizing Myopathy Following Interstitial Lung Disease with Anti-signal Recognition Particle Antibody

A 72-year-old man was admitted due to dyspnea on exertion with interstitial shadows and elevated serum creatinine kinase (CK). Despite a close examination, which included magnetic resonance imaging (MRI), we could not diagnose myopathy. Prednisolone was administered and gradually tapered. One year later, anti-signal recognition particle (SRP) antibody was confirmed and he was re-admitted for hypoxemia with elevated CK. MRI revealed muscle edema and a histopathological examination of a muscle biopsy specimen showed necrotizing myopathy. Prednisolone, cyclosporine, and intravenous immunoglobulin were administered. Physicians should carefully monitor muscle symptoms and serum CK levels in cases of interstitial lung disease with anti-SRP antibodies.

[Screening of autoantibodies associated with necrotizing myopathy among undiagnosed chronic myopathy]

We screened anti-signal recognition particle (SRP) and anti-3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMGCR) antibodies among 42 patients who had undiagnosed chronic myopathy from six national hospitals. Anti-SRP and anti-HMGCR antibodies were determined by RNA immuneprecipitation and enzyme-linked immune-sorbent assay (ELISA), respectively. We identified two patients with anti-SRP antibodies (4.7%) and, two with anti-HMGCR antibodies (4.7%). Both of anti-SRP-positive patients showed dysphagia with a high level of creatine kinase. Anti-HMGCR antibodies were associated with mild muscle weakness with a relatively late disease onset. Our study suggests the importance of autoantibody testing among undiagnosed chronic myopathy.

A case of amyloid myopathy diagnosed during the treatment of myopathy associated with anti-signal recognition particle antibodies

A 78-year-old man presented with subacute progressive proximal weakness and dysphagia. A biopsy specimen from the left biceps femoris revealed evidence of necrotic and regenerating muscle fibers, but lymphocyte infiltration was not noted. The patient was diagnosed with necrotizing myopathy with anti-signal recognition particle (SRP) antibodies. Concomitant therapy with prednisolone and azathioprine caused the serum CK level to return to normal and it caused clinical manifestations to abate. One year later, however, muscle weakness worsened. Immunoelectrophoresis of serum revealed IgG M protein, and muscle pathology revealed amyloid deposits in numerous blood vessels and at the periphery of a few muscle fibers, and deposits stained positive for anti-λ light chain antibody. The patient was diagnosed with amyloid myopathy, and therapy for systemic amyloid light chain amyloidosis caused muscle weakness to diminish. Amyloidosis is believed to be the primary pathology in this case based on the patient's response to treatment reaction, but the significance of a case involving both amyloid myopathy and necrotizing myopathy warranted examination.