September 2020

Detection of early changes in the muscle properties of the pectoralis major in breast cancer patients treated with radiotherapy using a handheld myotonometer

Authors: Yoon Kim 1, So Yeon An 2, Won Park 3, Ji Hye Hwang 4


  1. Department of Rehabilitation Medicine, National Rehabilitation Center, Seoul, Korea
  2. Center for Clinical Medicine, Samsung Biomedical Research Institute, Seoul, Korea
  3. Department of Radiation Oncology, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Korea
  4. Department of Physical and Rehabilitation Medicine, Samsung Medical Center, Sungkyunkwan University School of Medicine, Korea

Journal: Supportive Care in Cancer - September 2020, Volume 29, Pages 2581–2590 (DOI: 10.1007/s00520-020-05751-z)

Objective: The primary aim was to investigate serial changes in the mechanical properties of the pectoralis major (PM), upper trapezius (UT), and sternoclavicular mastoid muscle (SCM) in breast cancer patients undergoing radiotherapy (RT) using a hand-held myotonometer. The secondary aims were to determine changes in subjective symptoms and to identify correlation with subjective results.

Design: A total of 42 breast cancer patients were enrolled in this longitudinal prospective study. Muscle properties of the PM, UT, and SCM were evaluated before RT, immediately after RT, and 4 months post-RT. Subjective symptom scales of pain and stiffness at rest/stretch of each muscle were evaluated.

Results: The PM showed significant side-to-side differences; the affected PM showed increased tone, stiffness, and decreased elasticity compared with the unaffected PM. The affected PM and UT showed significant time-dependent interactions. Stiffness of the affected PM at stretching was significantly higher 4 months post-RT than baseline. Only the tone and elasticity of the affected PM were correlated with subjective symptoms.


Keywords: Breast cancer, Myotonometer, Pectoralis muscle, Radiation therapy, Trapezius muscle

In breast cancer patients who received RT after surgical management, increased tone and stiffness and decreased elasticity, as measured by a hand-held myotonometer, were observed on the affected PM compared with the unaffected side without significant time-side interactions. This change was sustained 4 months after RT, indicating the time-dependent effect of RT. Early changes in muscle properties immediately after RT preceded changes in subjective symptom scale scores, which worsened significantly 4 months post-RT compared with baseline.

Increased tone and stiffness were noted in the affected UT immediately after RT, and decreased 4 months later, indicating that sustaining an abducted and externally rotated shoulder posture during the RT session may have temporally influenced the muscle properties of the UT.

In conclusion, the MyotonPRO® is a promising evaluation tool for early detection of subclinical radiation-induced muscle fibrosis of the affected pectoralis muscle. Additionally, the portability, convenient usage, noninvasiveness, and objectivity of myotonometer allow physicians to easily check muscle conditions of irradiated patients in busy clinical settings. Myotonometer can also be a suitable objective outcome measure in further studies on various treatment trials for radiation-induced fibrosis of muscle.