Dermatomyositis — SCE Rheumatology MCQ

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ModerateMyositisDermatomyositisSCE Rheumatology

A 44-year-old woman presents with a 3-week history of Gottron papules and progressive symmetrical proximal weakness. Creatine kinase is 7,800 IU/L and anti-Mi-2 antibodies are detected. She has no chest pain, dyspnoea, palpitations or syncope. Her ECG and transthoracic echocardiogram are normal, but high-sensitivity cardiac troponin T is 58 ng/L (upper reference limit 14 ng/L). Which additional serum biomarker is most useful for distinguishing myocardial injury from troponin release associated with active skeletal muscle disease?

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Correct answer: B — High-sensitivity cardiac troponin I

Explanation lettering: D = shown as B · B = shown as C · C = shown as D

High-sensitivity cardiac troponin I is the most useful additional biomarker. In active inflammatory myopathy, regenerating skeletal muscle can express cardiac troponin T, producing an elevated troponin T concentration without primary myocardial injury. Troponin I is substantially more myocardium-specific in this context; an elevated result would therefore strengthen the indication for further cardiac assessment, potentially including cardiovascular magnetic resonance imaging. A is incorrect because CK-MB is also present in skeletal muscle and may rise substantially during active myositis, limiting its cardiac specificity. B is attractive because NT-proBNP reflects myocardial wall stress, but it is neither specific for myocarditis nor reliably elevated in subclinical myocardial inflammation; it is more useful when heart failure or haemodynamic dysfunction is suspected. C may show whether the troponin T concentration is dynamic, but serial elevation can continue to reflect skeletal muscle disease activity and does not resolve the source of release. E is a sensitive marker of muscle injury but cannot distinguish skeletal from cardiac muscle injury. The normal ECG and echocardiogram do not completely exclude subclinical myocarditis. If troponin I is elevated, cardiac symptoms emerge or other abnormalities develop, specialist cardiac evaluation should proceed despite initially reassuring investigations.

Reference: Cardiac troponin testing in idiopathic inflammatory myopathies and systemic sclerosis-spectrum disorders: biomarkers to distinguish between primary cardiac involvement and low-grade skeletal muscle disease activity (2015) — https://pubmed.ncbi.nlm.nih.gov/25732174/ Skeletal Muscle Disorders: A Noncardiac Source of Cardiac Troponin T (2022) — https://pubmed.ncbi.nlm.nih.gov/35389756/ Defining cardiac involvement in idiopathic inflammatory myopathies: a systematic review (2021) — https://pubmed.ncbi.nlm.nih.gov/34273157/