Paraspinal muscle asymmetry in Parkinson's disease.

Lateral postural deviation in Parkinson's disease (PD) is not uncommon but has never been radiographically queried to evaluate for specific muscle anatomy. Ten subjects (9 female) were identified with paraspinal asymmetry on examination and MRI. Relative atrophy was seen diffusely in all paraspinal muscles (psoas, interspinalis, quadratus, multifidus, longissimus and ileocostalis). The quadratus, multifidus, longissimus and ileocostalis were the most asymmetric and equally involved. The interspinalis was less asymmetric, whereas the psoas was almost never asymmetric. Fatty infiltrates, consistent with radiographic myopathic degeneration, were often seen in the atrophic muscles. In 8/10 cases, the side of PD symptom onset demonstrated the greatest atrophy. Lateral postural deviation appears to result from ipsilateral paraspinal atrophy with fatty infiltration. Correlation with the most affected side suggests causality.