Dermatomyositis

Diagnosis

Diagnosing dermatomyositis may require a combination of testing modalities. People with the disease may exhibit:

Test	Characteristic findings
Clinical exam	Characteristic pattern of muscle weakness Skin abnormalities (e.g., heliotrope eruption, Gottron sign, etc.)
Blood tests	Elevated creatine kinase (CK) and other muscle enzymes, such as aldolase, LDH, or AST, ALT. While AST and ALT are liver enzymes, they are also enzymes that can be secreted from the muscle. Specific antibodies indicative of myositis or other autoimmune diseases
Myositis Autoantibodies	Myositis-specific autoantibodies: Anti-synthetase antibodies such as Anti-Jo1, Anti-PL-12, Anti-Pl7, etc, Anti-Mi-2, Anti- NXP2, Anti-TIF-1 gamma, Anti-MDA5, Anti-SAE, (these are commonly seen in dermatomyositis) anti-HMGCR, anti-SRP (these are commonly seen in immune mediated necrotizing myopathy) Myositis-associated autoantibodies: Anti-PM-Scl, Anti-U1RNP, U3RNP, Anti-Ku
Assessment of electrical activity in muscles using EMG	Distinctive pattern of electrical activity in affected muscles, as assessed by electromyogram
Magnetic resonance imaging (MRI)	Signs of muscle inflammation
Muscle biopsy	Perifasicular atrophy, perivascular inflammation indicative of dermatomyositis (e.g., blood vessel inflammation)

References

1. Dalakas MC. Inflammatory Muscle Diseases. Longo DL, ed. N Engl J Med. 2015;372(18):1734-1747. doi:10.1056/NEJMra1402225
2. Baig S, Paik JJ. Inflammatory muscle disease – An update. Best Pract Res Clin Rheumatol. 2020;34(1):101484. doi:10.1016/j.berh.2019.101484

Last update: Feb 2023
Reviewed by Julie Paik, MD, MHS; Johns Hopkins University