Bent spine syndrome (BSS) is characterized by involuntary forward flexion of the trunk in the standing position but not in the recumbent position. We assessed the causes of BSS based on findings in 63 patients.

We retrospectively reviewed the records of all patients with BSS evaluated at a teaching hospital in Toulouse, France, between 1995 and 2006. For each patient, we recorded the findings from the following investigations: physical examination, electromyogram (EMG), creatine phosphokinase (CPK) assay, computed tomography (CT), and surgical muscle biopsy.

We identified 63 patients, 46 females and 17 males, with a mean age of 70±6.9years. Among them, 40 had delayed-onset paraspinal myopathy, with fatty infiltration predominantly affecting the paraspinal muscles. In 40% of these patients, CT disclosed mild fatty infiltration of the gluteal and posterior thigh and leg muscles in addition to the paraspinal muscle abnormalities. Paraspinal muscle histology showed lobular endomysial fibrosis, as previously described and ruled out other forms of muscle dystrophy. The remaining 23 patients (14 females and nine males) had either another neurological disease or myopathic involvement of other muscles, with a definite diagnosis; nevertheless, forward bending of the trunk was the most prominent symptom and the reason for the initial physician visit.

In our case-series, delayed-onset paraspinal myopathy accounted for 64% of cases of BSS. The most informative investigation was CT, which showed a patchy decrease in paraspinal muscle density.