Vaccination-induced myositis with intramuscular sterile abscess formation.

A case is presented of a 17-month-old female who acutely refused to bear weight on her left leg. A mass was felt and initially thought to represent a neoplasm. There were no constitutional symptoms. MRI demonstrated an area of edema involving the vastus medialis, vastus intermedius, and vastus lateralis with central fluid collection. Culture of the fluid component yielded no growth. Investigation determined the patient had received a DPT vaccination 10 days earlier into the thigh area of the left leg. This is the first MRI demonstration of vaccination-induced myositis with intramuscular sterile abscess formation.