Acquired lumbar kyphosis caused in adults by primary paraspinal myopathy. Epidemiology, computed tomography findings, and outcomes in a cohort of 23 patients

Abstract

Acquired lumbar kyphosis in adults, also called bent spine syndrome (BSS), is probably due to primary tardive myopathy affecting the paraspinal muscles. Objectives. To define family history and other factors associated with BSS, to score functional disability and pain in BSS using visual analog scales (VASs), to determine the pace of disease progression during follow-up, and to define computed tomography (CT) findings comparatively with age- and sex-matched controls. Patients and methods. Twenty-three patients (20 women and three men; mean age, 72.8 years) with a mean disease duration of 8.1 years at presentation and a mean follow-up of 3.5 years underwent a medical interview, a physical examination, and yearly CT scans with muscle density measurement at several vertebral levels (T4, T10, L1, L3, and L5). Results. Mean age at BSS onset was 64.6 years (range, 56–72). In 12 of the 23 cases, a family history of BSS was highly likely. Thirteen patients had performed heavy manual labor at some time during their lives. At completion of follow-up, the mean functional VAS score was 74.5 mm, the mean Eifel score was 16/24, and the mean pain VAS score was 72.4 mm. Mean muscle density obtained by pooling measurements at all vertebral levels was –12.6 ± 31 Hounsfield units (HU) in the patients and +36.9 ± 21 HU in the controls. During the 3.5-year follow-up, the mean loss in muscle density was 6.9 ± 16 HU in the patients; in contrast, no muscle density difference was found between two groups of low back pain patients without BSS aged 65 years and 72 years, respectively (36.2 ± 15 HU vs 38.6 ± 26 HU). Conclusion. BSS causes major functional disability and pain, which worsen over time. The decrease in paraspinal muscle density extends along the entire spine and becomes increasingly marked over time.