Predicting three-month functional outcomes after an ED visit for acute low back pain

Nearly 30% of patients who present to an ED with acute, new onset, low back pain (LBP) report LBP-related functional impairment three months later. These patients are at risk of chronic LBP, a highly debilitating condition. It has been reported previously that functional impairment, depression, and psychosomatic symptomatology at the index visit are associated with poor LBP outcomes. We wished to replicate those findings in a cohort of ED patients, and also to determine if clinical features present at one week follow-up could predict three-month outcomes in individual patients.

This was a planned analysis of data from a randomized comparative effectiveness study of three analgesic combinations conducted in one ED. Patients were followed by telephone one week and three months post-ED visit. The primary outcome was a three-month Roland-Morris Disability Questionnaire (RMDQ) score >0, indicating the presence of LBP-related functional impairment. At the index visit, we measured functional impairment (using the RMDQ), depressive symptomatology (using the Patient Health Questionnaire depression module), and psychosomatic features (using the 5-item Cassandra scale). At the one-week follow-up, we ascertained the presence or absence of LBP. We built a logistic regression model in which all the predictors were entered and retained in the model, in addition to socio-demographic variables and dummy variables controlling for investigational medication. Results are reported as adjusted odds ratios (adjOR) with 95% CI. To determine if statistically significant associations could be used to predict three-month outcomes in individual patients, we then calculated positive and negative likelihood ratios [LR(+) and LR(-)] with 95% CI for those independent variables associated with the primary outcome.

Of 295 patients who completed the study, 14 (5%) were depressed and 18 (6%) reported psychosomatic symptoms. The median index visit RMDQ score was 19 (IQR: 17, 21) indicating substantial functional impairment. One week after the ED visit, 193 (65%) patients reported presence of LBP. 294 patients provided a three-month RMDQ score, 88 of whom (30%, 95% CI: 25, 35%) reported a score >0. Neither depression (adjOR 0.7 [95% CI 0.2, 3.1]), psychosomatic symptomatology (adjOR 0.5 [95% CI 0.1, 2.0]), nor index visit functional impairment (adjOR 1.0 [95% CI 1.0, 1.1]) were associated with three-month outcome. Pain at one week was strongly and independently associated with the three-month outcome when examined at the group level (adjOR 4.0 [95% CI 2.1, 7.7]). However, likelihood ratios for pain or its absence at one-week were insufficiently robust to be clinically useful in predicting three-month outcomes in individual patients (LR+: 1.4 [95% CI: 1.3, 1.7]; LR-: 0.4 [95% CI: 0.2, 0.6]).

In spite of a strong association at the group level between presence of LBP at one week and functional impairment at three months, when used to predict outcomes in individual patients, presence of pain failed to discriminate with clinically meaningful utility between acute LBP patients destined to have a favorable versus unfavorable three-month outcome.