Association between pain, central sensitization and anxiety in postherpetic neuralgia

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Association between pain, central sensitization and anxiety in postherpetic neuralgia
Key Take-Away: 

Persistent nerve pain is one of the main complications of postherpetic neuralgia (PHN) but the mechanism causing pain is not really clear. In this study, the investigators have tried to address the huge area of unmet need by assessing the association between pain, central sensitization and anxiety.

In PHN, dorsal root ganglia neurons are damaged. According to the proposed models, PHN pain might be associated with nociceptive deafferentation, and peripheral (heat hyperalgesia) or central sensitization (allodynia).

ABSTRACT: 
Background: 

In PHN, dorsal root ganglia neurons are damaged.

According to the proposed models, PHN pain might be associated with nociceptive deafferentation, and peripheral (heat hyperalgesia) or central sensitization (allodynia).

Methods: 

In 36 PHN patients, afferent nerve fiber function was characterized using quantitative sensory testing and histamine-induced flare analysis.

Psychological factors were evaluated with the Hospital Anxiety and Depression Scale (HADS), disease-related quality of life (QoL) with SF-36 and pain with the McGill questionnaire [pain rating index (PRI)]. The patients were also divided into subgroups according to the presence or absence of brush-evoked allodynia as a sign of central sensitization.

Results: 

For all patients, warm, cold and mechanical detection was impaired (p < 0.001 each) and the size of the histamine flare was diminished on the affected side (p < 0.05); pain thresholds with the exception of brush-evoked allodynia (p < 0.05) were unaltered.

Correlation analysis revealed allodynia, anxiety, depression, QoL and age as relevant factors associated with pain severity (PRI). Allodynia was present in 23 patients (64%). In these patients, heat pain perception was preserved; the histamine flare was larger; the pinprick pain was increased as were McGill PRI sensory subscore, actual pain rating and almost significantly pain (McGill PRI) over the last 4 weeks.

Conclusion: 

PHN is associated with damage of afferent fibers. Central sensitization (i.e., allodynia) might contribute to PHN pain. There was a striking association between anxiety, depression and age, and the magnitude of PHN pain.

Eur J Pain 2015 Feb; 19(2):193-201

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