Anti-SRP Antibodies and Myocarditis in Systemic Sclerosis Overlap Syndrome with Immune-Mediated Necrotizing Myositis (IMNM)

Overlap syndrome of systemic sclerosis and idiopathic inflammatory myopathies is an increasingly frequent entity, but the association with immune-mediated necrotizing myositis has rarely been described. While myositis or myopathy may be features of scleroderma, it is imperative to correctly diagnose an overlap syndrome of these two, since it can be considered a different entity with specific management and a worse prognosis. Anti-signal recognition particle (anti-SRP) antibodies target the striated muscle fiber and inhibit myoblast regeneration, resulting in myofiber atrophy and necrosis. Anti-SRP antibodies are specific in immune-mediated necrotizing myopathy characterized by myonecrosis and minimal inflammatory reaction, with proximal muscle weakness and typical extra-muscular manifestation. There are controversial data on the association of cardiac manifestations and the presence of these antibodies, and recent studies cannot prove a significant correlation between the two. Myocarditis is a complication with an unpredictable, potentially severe outcome from heart failure and dilated cardiomyopathy to fatality. It can be difficult to diagnose, and a myocardial biopsy can be problematic in daily practice; thus, most practitioners rely on cardiac magnetic resonance with suggestive images for the correct diagnosis. This paper seeks to address the challenges associated with the diagnosis and treatment of collagen diseases by evaluating the role of anti-SRP antibodies in the pathogenesis of cardiac involvement.