Increased pressure pain sensibility in fibromyalgia patients is located deep to the skin but not restricted to muscle tissue

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Abstract
This study was aimed at comparing pressure pain sensibility in different tissues in fibromyalgia patients. Pressure pain thresholds (PPTs) were assessed in 16 fibromyalgia (FM) patients bilaterally at the bony part of epicondylus lateralis humeri, at the belly of m. extensor carpi ulnaris and at m. brachioradialis where the radial nerve branches pass underneath. Following a double-blind design, either a local anesthetic cream (EMLA) or a control cream was applied to the skin and PPTs were reassessed. The site with underlying nerve had a lower PPT than the bony site (P < 0.001) and the 'pure' muscle site (P < 0.001), respectively. These relations remained unaltered by skin hypoesthesia. The PPTs over the bony and the 'pure' muscle sites did not differ. Application of EMLA, compared to control cream, did not change PPTs over any area examined. The results demonstrated that pressure-induced pain sensibility in FM patients is not most pronounced in muscle tissue and does not depend on increased skin sensibility.