Tratamiento con rituximab para las miopatías necrosantes autoinmunes asociadas al anti-SRP: caso clínico y revisión de la evidencia

Anti-SRP immune-mediated necrotizing myopathy: A critical review of current concepts

Purpose of review

This review aims to describe clinical and histological features, treatment, and prognosis in patients with anti-signal recognition particle (SRP) autoantibodies positive immune-mediated necrotizing myopathy (SRP-IMNM) based on previous findings.

Previous findings

Anti-SRP autoantibodies are specific in IMNM. Humoral autoimmune and inflammatory responses are the main autoimmune characteristics of SRP-IMNM. SRP-IMNM is clinically characterized by acute or subacute, moderately severe, symmetrical proximal weakness. Younger patients with SRP-IMNM tend to have more severe clinical symptoms. Patients with SRP-IMNM may be vulnerable to cardiac involvement, which ought to be regularly monitored and cardiac magnetic resonance imaging is the recommended detection method. The pathological features of SRP-IMNM are patchy or diffuse myonecrosis and myoregeneration accompanied by a paucity of inflammatory infiltrates. Endoplasmic reticulum stress-induced autophagy pathway and necroptosis are activated in skeletal muscle of SRP-IMNM. Treatment of refractory SRP-IMNM encounters resistance and warrants further investigation.

Summary

Anti-SRP autoantibodies define a unique population of IMNM patients. The immune and non-immune pathophysiological mechanisms are involved in SRP-IMNM.

Belimumab for Immune-Mediated Necrotizing Myopathy Associated With Anti-SRP Antibodies: A Case Report and Retrospective Review of Patients Treated With Anti-B-Cell Therapy in a Single Center and Literature

Background

Immune-mediated necrotizing myopathy (IMNM) is characterized by markedly elevated creatinine kinase and histologically scattered necrotic muscle fibers and generally associated with autoantibodies against signal recognition particle (SRP) or 3-hydroxy-3-methylglutaryl-coA-reductase (HMGCR). Poor clinical response to conventional therapies and relapses commonly occur in severe cases. Anti-B-cell therapies have been used in refractory/relapsing cases.

Methods

The characteristics of a patient with IMNM associated with anti-SRP antibodies including physical examination, laboratory tests, and disease activity assessment were evaluated. Conventional therapy, belimumab treatment schedule, and follow-up data were recorded. Medical records of IMNM patients treated in our department from September 2014 to June 2021 were reviewed to evaluate the efficacy and safety of anti-B-cell therapy for anti-SRP IMNM. A literature review of patients with anti-SRP IMNM treated with anti-B-cell therapies was performed.

Results

We describe a case of a 47-year-old woman with IMNM associated with anti-SRP antibodies who relapsed twice after conventional therapy but showed good response and tolerance to belimumab at 28 weeks follow-up. In this review, three patients from our department were treated with rituximab. Two of the three patients rapidly improved after treatment. Twenty patients and five retrospective studies were included in the literature review. All patients were administered rituximab as an anti-B-cell drug.

Conclusion

Despite a lack of rigorous clinical trials, considerable experience demonstrated that anti-B-cell therapy might be effective for patients with IMNM associated with anti-SRP antibodies. Belimumab in association with steroids might be an encouraging option for refractory/relapsing cases.

Report of a case of necrotizing autoimmune myopathy with thymoma-associated myasthenia gravis

Purpose: Myasthenia gravis (MG) is an autoimmune disease and closely related to thymoma. Inflammatory myopathy may accompany with other autoimmune diseases. However, concurrence of inflammatory myopathy and MG is very rare. Necrotizing autoimmune myopathy (NAM), a rare form of inflammatory myopathy, is characterized by necrosis and regeneration of myocytes in proximal muscles without significant inflammation. The aim of the study was to report a rare case of NAM and concomitant thymoma-associated MG after thymectomy.Materials and methods/results: A 27-year-old female patient presented with muscle soreness and weakness in four limbs. Eyelid fatigue and neostigmine tests were negative, and no ptosis was found but the electromyographic examination (EMG) showed myogenic damage and a gradual decrease in the amplitude (20%) of EMG activities evoked by repetitive electrical stimulation. Antibodies against AChR and increased titer of creatine kinase were detected and plaque-like signals in both legs were found in magnetic resonance imaging. Myositis-related antibodies were negative but necrotic myocytes without inflammatory cell infiltration, and MHC-1 positive muscle fibers were found in muscle biopsy. Pathological examination confirmed anterior mediastinal B2 type thymoma. Five weeks after thymectomy, she started to show typical MG symptoms. No recurrence of thymoma was found but immunoassay showed a higher titer of AChR-Ab. Myositis-related antibodies negative necrotizing autoimmune myopathy (NAM) was reported to be associated with thymoma-associated MG.Conclusions: The patient showed symptoms related NAM but developed MG-related symptoms only after thymectomy. The mechanisms for the phenomena may be related to immune dysfunction associated with thymoma.