Reply: Respiratory Muscle ¹⁸F-FDG Uptake

REPLY: Thank you for your interest in our article (1). You have brought up very good and valid points we would like to address.

Patterns of uptake in the respiratory muscles are secondary to labored breathing regardless of the cause. Although it is true that this is not limited to chronic obstructive pulmonary disease (COPD), most patients in our study with this pattern were diagnosed with COPD (73%). Also, the inclusion bias of our study was limited to patients with suspected or established lung cancer. In addition, many of the patients with lung cancer present with pleural effusion at the time of imaging. However, in patients with pleural effusion, benign or malignant, there should not be the same respiratory muscle uptake as what is seen in COPD patients. To the best of our knowledge, none of the patients presented with an underlying restrictive process. Overall, we agree that labored breathing will cause this pattern of uptake whether it is restrictive, obstructive, or of other causes.

To remain consistent, we used the intensity of uptake in the mediastinum as the internal reference point. Given the diffuse and variable uptake in large muscles, we elected not to use another muscle as a reference. Several studies have been performed on various types of cancers showing that both the liver and the mediastinum are the most stable over time (2,3).