Use of the Rydel-Seiffer graduated tuning fork in the assessment of vibration threshold in postherpetic neuralgia patients and healthy controls

BACKGROUND AND AIMS: Afferent large fibre impairment has been reported as a useful predictor of postherpetic neuralgia (PHN) in patients with acute herpes zoster infection, using an electromechanical device to provide quantitative vibrametry. We aimed to demonstrate a clinically significant increase in vibration threshold in individuals with PHN compared to age-matched controls, using the portable and affordable Rydel-Seiffer graduated tuning fork. METHODS: We studied 45 PHN subjects aged over 55 years, and 45 age-matched controls with no history of herpes zoster infection. We excluded subjects with a history of disorders associated with neuropathy or immunocompromise. Measurements were performed at the ulnar styloid process and the head of the first metatarsal on the right side, in a warm room with the subject seated. Readings were taken in triplicate and the data analysed by a repeated measures design. RESULTS: We observed a significant difference in vibration threshold at both wrist and toe between the PHN and control groups (p <0.001). Age-stratification of subjects produced an increased and clinically useful difference between the two groups at both sites in subjects between 55 and 70 years (p <0.0001). CONCLUSIONS: We have shown a statistically significant decrease in vibration sensitivity in individuals with PHN aged 55-70 years compared to age-matched healthy controls, using the Rydel-Seiffer graduated tuning fork. A prospective study of patients with acute zoster infection is needed to determine the sensitivity and specificity of the graduated tuning fork in predicting PHN in patients with acute zoster infection.