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

Abstract

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.