Somatosensory findings in postherpetic neuralgia

Somatic sensory perception thresholds (warm, cold, hot pain, touch, pinprick, vibration, two-point discrimination), allodynia and skin temperature were assessed in the affected area of 42 patients with unilateral postherpetic neuralgia (PHN) and 20 patients who had had unilateral shingles not followed by PHN (NoPHN), and in the mirror-image area on the other side. There was no difference between the two groups for age or length of time after the acute herpes zoster infection. The PHN group showed significant changes in all sensory threshold measurements when the affected area was compared with the mirror-image area on the unaffected side, while the NoPHN group exhibited no threshold changes. Mechanical allodynia was present in 87% of the PHN group; half of the 12 patients with ophthalmic PHN showed extension of allodynia to the maxillary distribution. No differences in skin temperature were recorded between affected and unaffected regions in either group. Our findings show a deficit of sensory functions mediated by both large and small primary afferent fibres and also suggest major central involvement in the pathophysiology of the condition. If PHN does not occur following acute herpes zoster, recovery of neural functions appears to be good.