Classification of patients with incident non-specific low back pain: implications for research.

Background Context: Comparing research studies of low back pain is difficult because of heterogeneity. There is no consensus among researchers on inclusion criteria or the definition of an episode.

Purpose: This study aimed to determine pattern(s) of recurrent non-specific low back pain from data collected over 27 months.

Study Design/setting: This study used retrospective cohort study using administrative claims from multiple payers. Although claims are designed for capturing costs, not clinical complexity, they are valid for describing utilization patterns, which are not affected by potential "upcoding."

Patient Sample: The patient sample consisted of population-based, nationally generalizable sample of 65,790 adults with continuous medical and pharmaceutical commercial health insurance who received health care for incident, non-specific low back pain. Potential subjects were excluded for plausible cause of the pain, severe mental illness, or cognitive impairment.

Outcome Measures: Diagnostic and therapeutic health-care services, including medical, surgical, pharmaceutical, and complementary, received in inpatient, outpatient, and emergency settings were the outcome measures for this study.

Methods: The methods used for this study were latent class analysis of health-care utilization over 27 months (9 quarters) following index diagnosis of non-specific low back pain occurring in January-March 2009 and an analysis sample with 60% of subjects (n=39,597) and validation sample of 40% (n=26,193).

Results: Four distinct groups of patients were identified and validated. One group (53.4%) of patients recovered immediately. One third of patients (31.7%) may appear to recover over 6 months, but maintain a 37-48% likelihood of receiving care for low back pain in every subsequent quarter, implying frequent relapse. Two remaining groups of patients each maintain very high probabilities of receiving care in every quarter (65-78% and 84-90%), predominantly utilizing therapeutic services and pain medication, respectively. Probabilistic grouping relative to alternatives was very high (89.6-99.3%). Grouping was not related to demographic or clinical characteristics.

Conclusions: The four distinct sets of patient experiences have clear implications for research. Inclusion criteria should specify incident or recurrent cases. A 6-month clean period may not be sufficiently long to assess incidence. Reporting should specify the proportion recovering immediately to prevent mean recovery rates from masking between-group differences. Continuous measurement of pain or disability may be more reliable than measuring outcomes at distinct endpoints.