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