E018 COVID-19 vaccine-induced myositis
Authors: Thompson Luke , Nadin Thomas , Meiring James , Thomas Sally , Kumari Rakesh , Carter Stuart , Akil Mohammed , Alfred Arun , Morley Nick 
Published: April 2023

Abstract

Background/Aims
Through the COVID pandemic there have emerged reports of autoimmunity or new rheumatic diseases presenting in patients after they had COVID-19. This is thought to be caused by cross-reactivity of the COVID-19 spike protein to human antigens. Given the use of mRNA COVID-19 vaccinations which express the spike protein we might expect to see presentation of new rheumatic diseases following their use. We discuss a case where this appears to have occurred.

Methods
Our patient is a 24-year-old male with mixed phenotype acute leukaemia who had been treated with allogenic stem cell transplant and was currently in remission. He presented with fevers, palpitations, myalgia and bilateral arm and leg swelling. Symptoms began the day after receiving the first dose of an mRNA COVID-19 vaccination (Pfizer/BioNTech.) There were no other symptoms or recent change in medications. Physical examination revealed tender oedema in his forearms, biceps and thighs bilaterally with sparring of the hands. He had reduced power with shoulder (MRC 3/5), elbow (4), wrist (4+) and hip (4) movements. Observations revealed tachycardia and fevers up to 40C.

Results
Laboratory studies showed markedly elevated C-reactive protein (202), creatinine kinase (6697) and troponin (593) whilst investigations for infection were negative. An autoimmune panel was positive for anti-PM-SCL-75-Ab. An electrocardiogram showed sinus tachycardia. Echocardiogram was normal. Bilateral upper limb dopplers revealed no deep vein thrombus. An MRI of his thighs showed diffuse symmetrical oedema within the muscles, in keeping with an inflammatory myositis. A quadricep muscle biopsy showed evidence of MHC class 1 up-regulation, suggesting an inflammatory process. In addition, there were numerous macrophages evident in the endomysium. While this can be seen in graft-versus-host disease (GVHD), they would usually be found in the perimysium. After discussion between haematology, rheumatology and neurology, this was felt to be a case of vaccine induced myositis and myocarditis. Autoimmune myositis was thought to be less likely due to the relative sparing of the hands and the absence of Raynaud’s phenomenon. 1 gram of intravenous methylprednisolone was then given for 3 days. The patient had a marked response with defervescence, improving laboratory markers, improved myalgia and decreased limb swelling. The patient was stepped down to a reducing regime of prednisolone and discharged. Due to relapse whilst weaning he has started on mycophenalate mofetil and rituximab and now continues to improve.

Conclusion
There are case reports of myositis following COVID-19 vaccination but our patient’s case is complicated by the differential diagnosis of GVHD and concurrent myocarditis. Ongoing work is needed to clarify the exact link between vaccination and the presentation of a new inflammatory myositis, but it is important to recognise and start treatment early in order to preserve muscle bulk and ensure recovery.
Disclosure
L. Thompson: None. T. Nadin: None. J. Meiring: None. S. Thomas: None. R. Kumari: None. S. Carter: None. M. Akil: None. A. Alfred: None. N. Morley: None.