A 7-year old boy developed myositis secondary to intramuscular injection of benzathine penicillin-G in the context of secondary prophylaxis for rheumatic heart disease. Side effects of intramuscular delivery of benzathine penicillin-G are well described and include injection site pain and inflammation, but myositis, as depicted on magnetic resonance imaging in this case, has not previously been described.
Francis, J., Wyber, R., Remenyi, B. B., Croser, D., & Carapetis, J. (2016). Myositis complicating benzathine penicillin-G injection in a case of rheumatic heart disease. IDCases, 4, 6-7. https://doi.org/10.1016/j.idcr.2016.02.001