18F-FDG Uptake in Parsonage-Turner Syndrome

Area of Science:

• Oncology
• Neurology
• Radiology

Background:

• A 55-year-old male with large B-cell lymphoma presented with atraumatic left shoulder pain.
• F-FDG PET/CT showed increased uptake in the left supraspinatus and infraspinatus muscles, despite initial disease resolution.

Observation:

• An MRI revealed diffuse edema and enhancement in the shoulder muscles without a focal lesion.
• Muscle biopsy excluded lymphoma but showed signs of muscle denervation.

Findings:

• The clinical and imaging findings were consistent with Parsonage-Turner syndrome (acute brachial neuritis).
• This condition presented as a false-positive finding on F-FDG PET/CT.

Implications:

• Parsonage-Turner syndrome is an uncommon cause of shoulder pain in lymphoma patients.
• It can mimic disease progression or recurrence on PET/CT, necessitating careful differential diagnosis.