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dermatomyositis-dm-and-polymyositis-pm-pathogenesis-and-clinical-findings

Dermatomyositis (DM) and Polymyositis (PM): Authors: Merna Adly, Yan Yu* Reviewers: Nela Cosic Sean Doherty Martin Atkinson* * MD at time of publication Pathogenesis and clinical findings Immunogenetic and Cellular Predisposition Genetic polymorphisms cause dysregulated immune response, cytokine profile, and protein expression in muscle cells Demographics F:M, 2:1 Bimodal age distribution: - Juvenile: 7 years of age (mean) - Adult: 52 years of age (mean) Malignancy Tumor cells increase systemic inflammatory response, leading to increase of autoantigens associated with DM ↑ in DM-associated autoantibodies (Ex. Anti-Mi-2/ Anti-Jo-1) Autoantibodies bind to DNA or RNA in muscles, provoking a systemic inflammatory response ↑ chemokine and cytokine release in endothelial vasculature of muscles Perivascular Capillary necrosis inflammation Lack of blood supply to the myofibers causes endofascicular hypoperfusion and muscle ischemia Muscle tissue damage: Inflammatory infiltrates destroy cellular components of muscle (endoplasmic reticular, myofiber, and keratinocytes) Environmental triggers Infectious agents (ex. Picornavirus) or drugs (ex. statins) provoke immune response Elevated Antinuclear Antibodies Anti-Jo-1 Anti-OJ Anti-Mi2 Anti-SRP Anti-EJ Anti-PL12 Anti-PL7 These processes occur in the skin on the dorsum of the hands, forming hyperkeratotic flat red papules These processes occur in the upper & lower eyelids, causing red-purple discoloration +/- swelling Perifascicular atrophy (Observed on histology) Weaker GI tract musculature Weaker pulmonary musculature Weaker cardiac musculature Dermatomyositis only: Gottron Papules Heliotrope Rash Damaged muscle cells release their internal cellular enzymes into the bloodstream Elevation of muscle enzyme levels in serum: Creatinine kinase (CK), lactate dehydrogenase (LD), aldolase, aspartate aminotransferase (AST), and alanine aminotransferase (ALT) Muscle Biopsy Findings Muscle necrosis, fiber regeneration, diffuse CD8+ T lymphocytes infiltrates Bilateral Muscle Weakness Subacute development, primarily deltoids and hip flexors affected Dysphagia Aspiration, respiratory compromise Atrioventricular defects, tachyarrhythmias, dilated cardiomyopathy Legend: Pathophysiology Mechanism Sign/Symptom/Lab Finding Complications Published April 18, 2019 on www.thecalgaryguide.com