Introduction: The aim of this study was the characterization of the primary afferent functions with quantitative sensory testing (QST) and histamine iontophoresis in patients with postherpetic neuralgia (PHN), and their correlation to anxiety, depression, pain quality and quality of life.
Material and Methods: QST was performed in 38 patients with PHN (age 72±1 years) to determine thermal and mechanical detection- and pain thresholds. Histamine was applied by iontophoresis to elicit a flare reaction. The size of this flare was quantified. Anxiety and depression were evaluated with HADS, quality of life with SF-36, and pain quality with the McGill questionnaire.
Results: Affected areas were the face (n=8), the trunk (n=23), the leg (n=5) or the foot (n=2). Histamine flare size was diminished on the affected side (18.4±1.7cm2 vs. 14.7±1.9cm2, p<0.05). No correlation could be found between flare size and QST parameters.
Cold (CDT)-, warm (WDT)-, and mechanical detection thresholds (MDT) were enhanced on the affected side (p<0.001). However, heat- (HPT)-, cold-(CPT)-, and mechanical pain thresholds (MPT) did not differ between both sides. Allodynia occurred on the affected side only (p
Conclusion: Each QST parameter and flare size depends on the function of different nerve fibers, which might account for the missing correlation between these parameters. Flare size depends on histamine sensitive CMi (mechanoinsensitive C-fibers), WDT on CMH (mechanosensitive polymodal C-fibers), CDT on A-delta-fibers, MDT on A-beta-Fibers. The lack of any correlations between QST and flare reaction indicates that the amount of nerve fiber damage differs between each type of fiber. Therefore no single parameter alone is sufficient to characterize deafferentation in PHN. Interestingly, painfulness could not be explained by any sensory parameter, but depended on anxiety, depression and quality of life.
Supported by DFG (Bi 579/1, Bi 579/4) and BMBF (DFN-01EM0506).
