Antimitochondrial Antibody-associated Myopathy with Slowly Progressive Cardiac Dysfunction

Anti-mitochondrial antibody-positive inflammatory myopathy with multiple arrhythmias resistant to high-dose glucocorticoids and intravenous cyclophosphamide: a case-based review

Idiopathic inflammatory myopathies (IIMs) are a heterogeneous group of autoimmune diseases characterized primarily by muscle inflammation. Anti-mitochondrial antibodies (AMA) are typically associated with primary biliary cholangitis; however, they have also been linked to a rare subgroup of IIMs, namely "AMA-positive myositis," marked by a chronic disease course and muscle weakness, particularly affecting the paravertebral muscles, alongside muscle atrophy and cardiopulmonary complications. We report the case of a 40-year-old woman diagnosed with AMA-positive myositis, predominantly involving axial myopathy complicated by multiple arrhythmias and biopsy-proven focal segmental glomerulosclerosis with mitochondrial abnormalities on electron microscopy. The patient presented with progressive back pain and palpitations over a 3-month period. Although high-dose glucocorticoids and intravenous cyclophosphamide improved the axial myopathy and proteinuria, the cardiac condition remained unstable, necessitating permanent pacemaker implantation for persistent sinus dysfunction and radiofrequency catheter ablation for worsening atrial fibrillation (Af). Our literature review focusing on cardiac involvement in AMA-positive myositis revealed tachyarrhythmia was the most common (87.7%), particularly Af (55.4%), followed by cardiomyopathy (74.2%), myocarditis (43.2%), and bradyarrhythmia (40.0%). Arrhythmias and/or cardiac function deteriorated in 41.7% of patients treated with immunosuppressants and in 66.7% of patients treated without immunosuppressants, respectively. Furthermore, in the treated group, more patients with worsened cardiac lesions required additional electronic devices compared to those without (53.3% vs. 4.8%). Early detection and adequate management of cardiac complications in AMA-positive myositis are critical to prevent irreversible myocardial damage and fatal outcomes. In addition to cardiac complications, concomitant renal involvement associated with AMA-positive myositis may be also considered.

A Serial Assessment of T1 and T2 Mapping Cardiac Magnetic Resonance Before and After Heart Failure Onset in a Case of Cardiomyopathy in Anti-mitochondrial Antibody-positive Myositis

A 69-year-old woman presented with heart failure and progressive muscle weakness and was diagnosed as anti-mitochondrial antibody (AMA) myositis with cardiac involvement. Immunosuppressive therapy with prednisolone and intravenous cyclophosphamide significantly improved the symptoms, hemodynamics, and cardiac function. Cardiac magnetic resonance (CMR) T1 and T2 mapping showed elevated native T1, T2, and extracellular volume fractions during heart failure exacerbation (day 37) compared to pre-hospitalization values (10 months before admission) and follow-up conducted 6 and 12 months after admission. This case underscores the importance of comprehensive evaluation, such as serial CMR imaging and immunosuppressive therapy, in managing myocardial involvement in AMA-positive myositis.

Anti-mitochondrial antibodies in systemic sclerosis target enteric neurons and are associated with GI dysmotility

Background

Most patients with systemic sclerosis (SSc) experience gastrointestinal (GI) dysmotility. The enteric nervous system (ENS) regulates GI motility, and its dysfunction causes dysmotility. A subset of SSc patients harbor autoantibodies against the M2 mitochondrial antigen (AM2A). Here, we investigate whether M2 is expressed by specific ENS cells, and if AM2A associate with GI dysmotility in SSc patients.

Methods

Sera from 154 well-characterized patients with SSc were screened for AM2A by ELISA. Clinical features and GI transit data were compared between AM2A-positive and negative patients. HepG2 cells were cultured with these sera and co-stained with AM2A.

Results

Nineteen of 147 patients (12.9%) were AM2A positive. AM2A positivity was significantly associated with slower transit in the esophagus (β -14.4, 95%CI -26.2, -2.6) and stomach (β -7.9, 95% CI -14.1, -1.6). Immunostaining demonstrated pan-mitochondrial antigens TOM-20 and M2 enrichment in human ENS neurons, specifically in mesoderm-derived enteric neurons (MENS). HepG2 cells cultured with SSc sera showed that SSc autoantibodies penetrate live cells and that AM2A and other SSc autoantibodies are localized to subcellular compartments containing target antigens.

Conclusion

AM2A in SSc patients associate with slower GI transit. MENs are enriched in mitochondria, suggesting enhanced susceptibility to mitochondrial dysfunction and associated GI dysmotility in SSc. Our finding that SSc autoantibodies penetrate live cells in vitro suggests that SSc-AM2A may penetrate MENs in vivo, driving ENS and GI dysfunction. Further studies are warranted to understand whether AM2As contribute to mitochondrial dysfunction, and whether mitochondrial dysfunction contributes to GI dysmotility in SSc.

Sick sinus syndrome concomitant with myopathy associated with anti-mitochondrial antibodies: a case report

Background

Anti-mitochondrial antibody (AMA)-associated myopathy is known to be concomitant with primary biliary cirrhosis and to cause both skeletal muscle disorders and arrhythmias, myocardium disorders, and respiratory muscle disorders. We report a case of AMA-associated myopathy in which the bradycardia-related symptoms preceded the skeletal muscle symptoms.

Case summary

A 59-year-old woman visited the emergency room in our hospital following a syncopal event. The patient was bradycardiac (45 b.p.m.) with a junctional rhythm resulting from sick sinus syndrome (SSS) and was suffering from heart failure. Blood tests revealed elevated creatine kinase (CK) and hepatic enzymes. She underwent permanent pacemaker implantation. However, it proved difficult to detect the electrical potential in the right atrium. Although successful atrial pacing was achieved at the lower right atrial septum, the atrial threshold was markedly high and she depended on ventricular pacing. One year later, neurological examination and muscle biopsy confirmed the diagnosis of AMA-associated myopathy. Following this diagnosis, steroid pulse therapy was initiated. Steroid administration relieved her symptoms and lowered the CK levels but the atrial standstill persisted. The patient takes low-dose prednisolone and has had an uneventful course for 3 years.

Discussion

To the best of our knowledge, this is the first case of AMA-associated myopathy diagnosed by the first symptom related to bradycardia due to SSS. Patients with AMA-associated myopathy can experience a variety of cardiac symptoms, including arrhythmias, and initially complain of cardiac symptoms without symptoms of skeletal myopathy. This disease should be considered when diagnosing patients with arrhythmia and elevated CK.

Refractory ventricular tachycardia and heart failure due to anti-mitochondrial antibody-positive inflammatory myopathy

BACKGROUND

Anti-mitochondrial antibody (AMA)-positive inflammatory myopathy, a rare type of idiopathic inflammatory myopathy which was frequently difficult to diagnose, can affect muscles and the structure and electrical conduction of the heart. Early identification and treatment of this myopathy can prevent serious cardiovascular adverse events and improve cardiac function.

CASE PRESENTATION

We report a patient who experienced repeated syncope, ventricular tachycardia (VT) and heart failure accompanied by weakness and muscle atrophy. He was initially diagnosed with dilated cardiomyopathy and received implantable cardioverter-defibrillator therapy. He was subsequently misdiagnosed as muscular dystrophy due to progressive muscular atrophy. However, the patient developed repeated and refractory VT storms that were not alleviated by conventional therapy. Finally, he was diagnosed with AMA-positive inflammatory myopathy with cardiac injuries. The patient was markedly recovered by being treated with immunosuppressive and immunomodulatory therapy.

CONCLUSION

AMA could be screened when discovering myopathies accompanied by unexplained cardiac symptoms. Our findings provide insights into the diagnosis and therapy of this rare and severe disease.

The effect of immunosuppressive therapy on cardiac involvements in anti-mitochondrial antibody-positive myositis

AIMS

Anti-mitochondrial antibody (AMA)-positive myositis is frequently associated with various cardiac involvements, such as arrhythmia and left ventricular (LV) dysfunction. However, the efficacy of immunosuppressive therapy in these complications remains unknown. This study aimed to investigate the cardiac response to immunosuppressive therapy in patients with AMA-positive myositis.

METHODS AND RESULTS

The clinical data of 15 AMA-positive myositis patients with cardiac involvement were retrospectively collected at our centre. To evaluate the effects of immunosuppressive therapy, echocardiographic and laboratory data of patients who received glucocorticoid therapy with additional immunosuppressants (n = 6) and those who did not (n = 6) were compared. Also, the characteristics of patients with or without >5% LV ejection fraction (LVEF) decline during the follow-up period (n = 5 vs. n = 7) were compared. Thirteen patients (87%) had arrhythmias, and eight patients (53%) had LV wall motion abnormalities. Although arrhythmias decreased after treatment, reduced LVEF and LV wall motion abnormalities persisted. Further investigation revealed an increased LV end-systolic dimension and reduced LVEF in patients without additional immunosuppressive therapy, while those in patients with additional immunosuppressive therapy were maintained. Six of seven patients (86%) without LVEF decline received additional immunosuppressive therapy, whereas no patients with LVEF decline had additional immunosuppressive therapy.

CONCLUSIONS

Cardiac involvement in AMA-positive myositis may worsen even with glucocorticoid monotherapy, and there might be some associations between the change of LV function and additional immunosuppressive therapy.

Differential diagnosis of necrotizing myopathy

PURPOSE OF REVIEW

Necrotizing myopathy is a broad term. It includes patients with the recently described immune-mediated necrotizing myopathies (IMNM) who have specific antibodies, such as anti-hydroxy-3-methylglutaryl-CoA reductase or anti-signal recognition particle, seronegative phenotypes that can be associated with cancer, and other types of myositis and connective tissue diseases involving necrotic muscle fibers as a characteristic pathologic feature. Necrotizing myopathies that are not immune-mediated, such as those caused by drugs, dystrophies, infections, or even hypothyroidism are also included. The purpose of this review is to address the differential diagnosis of these disorders.

RECENT FINDINGS

New IMNM have been described over the last few years, some of them related with checkpoint inhibitors, drugs that are being increasingly used in cancer treatment. Necrotizing myopathy has also been reported in association with specific phenotypes and autoantibodies (e.g. anti-Mi2 dermatomyositis, antisynthetase syndrome, and myositis associated with antimitochondrial antibodies). Rarer cases associated with graft-versus-host disease and severe acute respiratory syndrome coronavirus 2 infection are also emerging.

SUMMARY

Differentiation between patients with IMNM and those without the superimposed autoimmune phenomena helps clinicians determine the best individualized approach to use and the appropriate immunosuppressive therapy, whenever needed.