The reliability of depression diagnosis in chronic low back pain. A pilot study

The variability in estimated rates of major depressive disorder (MDD) in chronic pain samples may be accounted for by sample and methodological differences. Most studies rely on a single measure of depression and lack independent or repeated measures. This study investigated the prevalence of psychiatric disorders in a convenience sample of 18 patients disabled by low back pain (LBP) referred to, evaluated, and treated in a comprehensive pain rehabilitation program specifically designed to restore work readiness and return to work. Subjects had one or more spinal conditions, had work-related back pain for more than 6 months (x = 23.8), were Caucasian, predominantly young (x = 37.5) and male (55%), and were disabled on workers' compensation and approved for rehabilitation. The performance of three diagnostic procedures, the Pain Medicine Evaluation, an independent Structured Clinical Interview for DSM-III-R (SCID), and Longitudinal Clinical Diagnosis were compared with the "gold standard" of the Final Diagnosis which incorporated information from the other three. Also, the performance of a questionnaire, The Pain & Mood Structural Interview (PMSI), designed to assess the causal relationship of pain and mood and specifically the confounding effects of physical factors, was examined. Thirteen of 18 patients (72%) were diagnosed with MDD at Final Diagnosis. MDD diagnosis was made on 4 of 18 patients (22%) on the initial Pain Medicine Evaluation and on 9 of 18 patients (50%) on the SCID, with only 1 ruled out by the confounding questionnaire, for a SCID current prevalence of 44%. Both the SCID and Pain Medicine Evaluation accurately diagnosed the MDD cases they identified; 9 of 13 MDD cases (69%) were precipitated by a physical factor other than their pain. Three episodes of MDD were ruled out by confounding. These findings are discussed in relation to their implications for assessing pain patients for psychiatric comorbidity.