“…Psychiatric comorbid disorder and chronic pain syndrome may present together without sharing the same pathophysiological mechanisms. There are studies reporting that the endogenous analgesia system in CDH patient groups is altered and defective (Fusco et al, 1997; Hering et al, 1993; Sarchielli et al, 2001; Schnider et al, 1995; Siniatchkin et al, 1998; Srikiatkhachorn et al, 1994), also in experimental studies it has been shown that chronic use of analgesics may alter central 5‐HT system (Sandrini et al, 1993; Srikiatkhachorn et al, 2000). There are also studies reporting that muscle tension is higher in chronic pain patients with depression and depressed patients magnify the medical symptoms (Fishbain, 1999; Katon, 1997).…”