Anakinra injection site reaction on FDG PET/CT

Area of Science:

• Rheumatology
• Nuclear Medicine

Background:

• Adult-onset Still's disease (AOSD) is a rare systemic inflammatory disorder of unknown cause.
• Key features include fever, arthritis, rash, and elevated ferritin levels.

Observation:

• A 29-year-old female patient with AOSD underwent an FDG PET/CT scan.
• The scan demonstrated lymphadenopathy, splenomegaly, and bone marrow hypermetabolism, indicative of active AOSD.
• Additionally, FDG-avid subcutaneous lesions at injection sites were noted.

Findings:

• The observed subcutaneous lesions corresponded to anakinra injection sites.
• These findings suggest that anakinra injections can cause FDG-avid reactions in patients with AOSD.
• These reactions may be misinterpreted as disease progression on FDG PET/CT.

Implications:

• FDG PET/CT findings at anakinra injection sites should be carefully evaluated in AOSD patients.
• Distinguishing these reactions from active disease is crucial for accurate treatment monitoring.
• This highlights the importance of correlating imaging findings with clinical history and treatment regimens.