Figure 2. Hierarchical cluster analysis of patient subgroups defined by constellations of pain-related symptoms and signs.

(A) Individual patients are symbolized by short vertical lines at the bottom of the dendrogram. Horizontal lines indicate similarities between the patients' pain, whereas upper vertical lines represent differences between pain-related signs or symptoms. At the indicated separation threshold (arrow), we identified eight subgroups of patients (clusters C1 to C8) with distinct constellations of pain-related symptoms and signs (pain subtypes). (B) Patients with DN, PHN, and radicular LBP were distributed across the clusters C1 to C6, whereas patients with axial LBP almost exclusively formed the clusters C7 and C8.