Identification of a new target muscle for treatment in patients with Parkinson's disease who have lateral trunk flexion?

Parkinson's disease (PD) can present with lateral trunk flexion (LTF). Abnormal posture associated with PD has been treated, but the effectiveness of these treatments is limited, resulting in unsatisfactory outcomes. Unilateral hypertrophy and unilateral hyperactivity may be useful for deciding targets for injection of botulinum toxin or physical rehabilitation. However, such findings may be limited such as the obliquus abdominis muscle or thoracic paraspinal muscles, and several other muscles may have a causative role in LTF. We investigated 8 patients whether other muscles show unilateral hypertrophy by analyzing computed tomographic scans. Cobb's angle was 11° to 34°. The area of the paravertebral muscles was large contralateral to the bending side and this trend intensified from L4 to Th10. The lumbar quadrate muscle and psoas major muscle showed unilateral enlargement. These larger muscles were prominent contralateral to the bending side in five patients and ipsilateral to the bending side in two patients. This unilateral muscle change was mildly seen in the internal and external abdominal oblique muscles. The lumbar quadrate muscle or psoas major muscle showed two hypertrophic patterns, and these muscles might be new therapeutic targets for treatments such as botulinum toxin.