**4.2.5 Cytokines**

There are several direct and indirect pathways that link cytokines with nociception or hyperalgesia (Coutaux et al., 2005; Sommer & Kress, 2004; Uceyler et al., 2009). Four studies investigated cytokines in chronic trapezius myalgia, but significant differences were only found for active trigger points (Shah et al., 2008; Shah et al., 2005). These studies, however, used very few subjects, an obvious limitation. Larger studies have not found elevated levels of cytokines (Larsson et al., 2008; Rosendal et al., 2005). On the other hand, these studies might have had some technical problems due to the catheters used, also a limitation. However, the chronic WAD study found increased IL-6 (Gerdle et al., 2008c).
