Typology of patients with fibromyalgia: cluster analysis of duloxetine study patients (BMC Musculoskeletal Disorders)

Background: To identify distinct groups of patients with fibromyalgia (FM) with respect to multiple outcome measures. Methods: Data from 631 duloxetine-treated women in 4 randomized, placebo-controlled trials were included in a cluster analysis based on outcomes after up to 12 weeks of treatment. Corresponding classification rules were constructed using a classification tree method. Probabilities for transitioning from baseline to Week 12 category were estimated for placebo and duloxetine patients (Ntotal = 1188) using logistic regression. Results: Five clusters were identified, from `worst` (high pain levels and severe mental/physical impairment) to `best` (low pain levels and nearly normal mental/physical function). For patients with moderate overall severity, mental and physical symptoms were less correlated, resulting in 2 distinct clusters based on these 2 symptom domains. Three key variables with threshold values were identified for classification of patients: Brief Pain Inventory (BPI) pain interference overall scores of