Increased muscular FDG uptake could be due to various causes. Detailed analysis combined with history might be helpful for image interpretation. We present FDG PET/CT findings of a 69-year-old woman with lung cancer. The images demonstrated intense FDG uptake in multiple muscles, likely due to cough before the PET/CT study. To relieve the patient’s cough, codeine was administrated. The second 18F-FDG PET/CT was performed 2 days later. The images showed that the abnormal muscular activity had become decreased, which was slightly lower than hepatic activity.