Polymyositis and raised troponin after mRNA COVID‐19 vaccination

Abstract

A previously well 36-year-old man presented to hospital 6 days after receiving his first BNT162b2 mRNA COVID-19 vaccine into the left deltoid. He presented with a 3-day history of subjective fevers and bilateral thigh and calf pain. Physical examination demonstrated normal lower limb neurology. He had no other extramuscular manifestations of inflammatory myositis. Laboratory investigations notably included raised D-dimer 1.09 mg/L, creatinine kinase 6044 unit/L, lactate dehydrogenase 393 unit/L, C-reactive protein 29 mg/L, alanine aminotransferase 782 unit/L and aspartate aminotransferase 480 unit/L. Screening was negative for antinuclear antibodies, extractable nuclear antigens and myositis-specific antibodies. Lower limb venous dopplers and computed tomography pulmonary angiogram were negative for thromboses. Magnetic resonance imaging (MRI) of bilateral thighs demonstrated extensive myoedema (Fig. 1A,B). A right thigh biopsy confirmed the diagnosis of immune-mediated polymyositis (Fig. 1C–H). A troponin I test was sent at the time of presentation due to the raised D-dimer, although there were no symptoms of chest pain or shortness of breath. The troponin I was elevated at 296 ng/L and normalised to 12 ng/L after polyethylene glycol (PEG) extraction. The troponin I was also discrepant from the troponin T, which was minimally elevated at 25 ng/L. Transthoracic echocardiogram and cardiac MRI were not supportive of myocarditis, and this diagnosis was deemed unlikely. Taken together, this suggested the presence of interfering antibodies causing elevation of the troponin I assay result rather than true myocardial damage. A diagnosis of myositis likely secondary to the COVID-19 mRNA vaccine was made based on the clinical presentation, temporal association and confirmatory imaging and biopsy findings. A short tapering oral corticosteroid course was commenced, with subsequent clinical and biochemical improvement and reversal of MRI findings. This is the first case to report concurrent polymyositis and likely spuriously elevated troponin following mRNA COVID-19 vaccination. While the overall benefits of vaccination certainly outweigh the risk of adverse events, it is important for clinicians to be aware of potential immune-mediated vaccine complications. Several immune-related adverse effects of SARS-CoV-2 vaccination have previously been reported, including myositis after mRNA vaccination.1-3 Reports have also described inflammatory myositis after ChAdOx1 nCoV-19.4 However, no reports thus far have described the phenomenon of raised troponin I secondary to interfering antibodies following mRNA COVID-19 vaccination. Therefore, this should be a consideration for clinicians faced with a raised troponin in the absence of clinical or radiological evidence supporting myocardial damage, particularly given the current concerns of myocarditis following mRNA vaccination. Indeed, previous reports from the general hospital population have described patients with elevated troponin I that improves with PEG extraction, suggesting the presence of interfering antibodies.5 Furthermore, it is noteworthy that troponin I is not typically elevated with inflammatory myopathies, whereas troponin T elevation is common.6 Overall, this case presents two rare post-vaccination clinical phenomena, but should more generally encourage clinicians to consider a broad differential that includes immune-related adverse events for patients presenting after mRNA COVID-19 vaccination.

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