Changes in muscle tone and stiffness around shoulder associated with radiotherapy in breast cancer patients

Introduction/Background Treatment related shoulder dysfunction and anterior chest wall stiffness is common in breast cancer patients. Radiotherapy is known to alter the properties of muscles such as fibrosis, but it is difficult to objectively assess. Objective measurements of muscle properties can be useful for evaluating these problems and the effect of intervention. Our study aimed to assess changes in serial muscle properties associated with radiotherapy in breast cancer patients using MyotonPRO, device measuring muscle properties. Material and method Thirty-five breast cancer patients who underwent mastectomy and scheduled to undergo radiotherapy were enrolled. Frequency (tone, Hz) and stiffness (N/m) were measured in both pectoralis major (PM), sternocleidomastoid (SMC) and upper trapezius (UT) before radiotherapy and immediately after radiotherapy. Paired t -test was used to investigate the side-to-side difference and changes associated with radiotherapy of tone and stiffness of muscles around shoulder. Results Before radiotherapy, the stiffness and tone of affected PM were significantly higher than unaffected PM. Immediately after radiotherapy, the stiffness and tone of affected PM were still significantly higher than unaffected PM and the difference became larger than before radiotherapy. Although there was no side-to-side difference of parameters before radiotherapy, the stiffness of affected UT was significantly higher than unaffected UT immediately after radiotherapy. Stiffness/tone of affected PM and affected UT increased significantly immediately after radiotherapy compared to before radiotherapy. Conclusion After operation, only the tone and stiffness of affected PM were increased. After radiotherapy, the stiffness and tone of affected PM were higher than before radiotherapy, and the tone and stiffness of affected UT were also increased. Our findings confirmed that surgical treatment and radiotherapy affect the stiffness and tone of affected PM. And stiffness and tone of affected UT increased before and after radiotherapy, which is thought to be due to posture of receiving radiotherapy.