SERONEGATIVE AUTOIMMUNE NECROTIZING MYOPATHY: ITS COURSE ACCELERATED BY COXSACKIE B INFECTION

Abstract

TOPIC: Critical Care TYPE: Medical Student/Resident Case Reports INTRODUCTION: We present a patient with necrotizing myopathy and rapid progression of muscle weakness, including respiratory muscles, leading to hypercapnic respiratory failure requiring mechanical ventilation following a myopericardial infection thought to be secondary to coxsackie B virus (CVB). This suggests that CVB accelerated the progression of the antibody-negative Immune mediated necrotizing myopathy (IMNM). CASE PRESENTATION: A 43 year old woman was hospitalized with proximal muscle weakness for 4 months with 2 weeks of substernal chest pain, which worsens when lying down and relieved when leaning forward. Progressive dyspnea on exertion and led to hypercapnic respiratory failure requiring mechanical ventilation. Laboratory and imaging findings were significant for creatinine kinase of 4,796, a troponin of 6.22, elevated antibody titers for CVB 1-6, and a pericardial effusion on echocardiogram. Pertinent negatives include acetylcholine receptor antibody (ab), antinuclear ab, skeletal muscle ab, Anti-signal recognition particle (SRP) and anti-hydroxy-3-methylglutarylCoA reductase (HMGCR) auto-ab. Due to a suspicion for inflammatory myopathy on MRI, a biopsy of quadriceps muscle showed predominant necrosis with minimal inflammation (monocytes, lymphocytes), myophagocytosis, and patchy MHC upregulation. Electromyogram (EMG) was negative for neuropathy or myasthenia gravis [4]. The constellation of findings was consistent with autoimmune necrotizing myopathy, its course complicated by myopericarditis thought to be secondary to CVB. The patient received IVIG, rituximab and high dose steroids, and was discharged to a long term acute care facility, where the patient's strength gradually improved. She was eventually weaned off of ventilator support. DISCUSSION: Necrotizing myopathy is a relatively recently defined form of autoimmune myopathy characterized by less inflammation and more necrosis in muscle tissue than seen in polymyositis [1]. Autoimmune myopathies are rare, with a prevalence of 9–14 cases per 100,000 people [5, 6]. Seronegative IMNM has not been characterized as well as seropositive IMNM [4]. While European Neuromuscular Centre criteria do not require muscle biopsy to diagnose seropositive IMNM, a muscle biopsy is essential/required for diagnosis of seronegative IMNM [3, 4]. CONCLUSIONS: In the setting of myocarditis likely secondary to CVB, the patient's myopathy rapidly worsened to include respiratory muscles and led to mechanical ventilation. This course of events strongly raises the possibility that coxsackie B infection led to acceleration of myopathy. REFERENCE #1: Adler BL, Christopher-Stine L. Triggers of inflammatory myopathy: insights into pathogenesis. Discov Med 2018;25:75–83. REFERENCE #2: Dalakas MC. Myositis: are autoantibodies pathogenic in necrotizing myopathy? Nat Rev Rheumatol 2018;14:251–2. REFERENCE #3: Khan NAJ, Khalid S, Ullah S, et al. Necrotizing autoimmune myopathy: a rare variant of idiopathic inflammatory myopathies. J Investig Med High Impact Case Rep 2017;5:232470961770903. DISCLOSURES: No relevant relationships by Erik Anderson, source=Web Response No relevant relationships by Amanda Eng, source=Web Response No relevant relationships by Padmanabhan Krishnan, source=Web Response