Intracutaneous histamine injection can detect damage of cutaneous afferent fibres in postherpetic neuralgia.

BACKGROUND

The axon reflex response in diseased skin of patients with postherpetic neuralgia may be significantly impaired.

OBJECTIVE

In the present study we introduced a simple test for quantifying the decreased axon reflex flare response in the clinical routine.

METHODS

Histamine was intradermally applied to the diseased dermatome as well as to the corresponding dermatome of the contralateral side of the body. Ten minutes after application, skin blood flow and the extension of the hyperaemic response were assessed by means of laser Doppler scanning.

RESULTS

In the skin region affected by the postherpetic neuralgia, the hyperaemic area was significantly smaller than in the healthy skin. The mean flux values did not differ significantly between the two sites. There was no correlation between the hyperaemic response and the intensity of pain sensation assessed by a clinical visual analogue score.

CONCLUSION

The smaller hyperaemic area in the dermatome with postherpetic neuralgia strongly indicates a C fibre or C nociceptor damage. We consider histamine injections as a useful tool in the differential diagnosis of postherpetic neuralgia.