Rheumatology: Polymyositis and Dermatomyositis reading Flashcards
- Review the classification scheme for inflammatory myopathies.
- Describe the clinical and laboratory features of polymyositis and dermatomyositis including EMG, MRI and biopsy findings.
- Describe the clinical and laboratory features of polymyositis and dermatomyositis including EMG, MRI and biopsy findings
EMG findings: a myopathic pattern - increased insertional activity (abnormally increased activity when the EMG needle is inserted) and spontaneous fibrillations, decreased amplitude of motor unit action potentials, and complex repetitive discharges. Always obtain EMG on one side and obtain the muscle biopsy on the contralateral side as not to complicate the interpretation of the biopsy.
MRI findings: can demonstrate areas of muscle inflammation, edema with active myositis, fibrosis, and calcinosis; can be used to guide the optimal site for biopsy and define the response to therapy.
- Describe the clinical and laboratory features of polymyositis and dermatomyositis including EMG, MRI and biopsy findings
- Discuss the clinical and laboratory features of the Anti-synthetase Syndrome including anti-synthetase antibodies.
1. Myositis-specific antibodies
a. Anti-synthetase antibodies: Directed against aminoacyl-tRNA synthetases (a family of enzymes whose role is to catalyze the attachment of a particular amino acid to its transfer RNA).
Anti-Jo-1 = anti-histidyl-tRNA synthetase (present in 15-30% of PM and 60- 70% of anti-synthetase syndrome). Antibodies against several other aminoacyl-tRNA synthetases have been discovered and occur less frequently (<5%). Clinical association: anti-synthetase syndrome (see above).
- Contrast the cellular differences in the pathology of polymyositis and dermatomyositis.
- List the evidence suggesting viral infections as a cause or triggering factor in polymyositis or dermatomyositis
- Discuss the treatment of inflammatory myopathies as it relates to pathophysiology.
