Dynamic of the somatosensory system in postherpetic neuralgia

In postherpetic neuralgia (PHN) different types of patients can be distinguished regarding their predominant peripheral nociceptor function.

The aim was to examine somatosensory profiles in the course of disease with special regard to the different subtypes existing in PHN.

Twenty patients with PHN (7 men and 13 women, age 67 ± 9.6 years) were examined at baseline (disease duration 18.1 ± 26 months) and follow-up (31.6 ± 23.8 months later) with quantitative sensory testing (protocol of the German Research Network on Neuropathic Pain).

Fourteen (70%) PHN patients presented with impaired (iPHN) and 6 (30%) with preserved (pPHN) C-fiber function. Groups did not differ regarding age, disease duration, or pain intensity at baseline. Both groups did not differ regarding change in pain intensity (-0.5 ± 2.3 vs -1.7 ± 2.6 numerical rating scale, P = n.s.) at follow-up. Impaired PHN improved in thermal and mechanical detection thresholds as well as allodynia independent from change in pain intensity. By contrast, pPHN showed an increase in mechanical pain sensitivity (1.4 ± 2.5 vs -0.4 ± 2.2, P < 0.05) and a trend towards a stronger loss of detection (66% vs 33%, P = n.s.) on follow-up.

Results demonstrate that patients with preserved C-fiber function are more predisposed to develop signs of central sensitization as demonstrated by an increased mechanical pain sensitivity. Impaired C-fiber function is able to improve even in chronic cases, but a functional loss is unlikely to play a role here. The knowledge of development of somatosensory profiles in the course of the disease offers possibilities to optimize a mechanism-based treatment.