Quantifying allodynia in patients suffering from unilateral neuropathic pain using von frey monofilaments

The aim of this study is to investigate whether quantitative sensory testing with Von Frey monofilaments (VFMs) can be used for the quantification of allodynia in patients with chronic neuropathic pain, and how the pain threshold of affected skin differs from healthy skin.

Using VFMs, we aimed to determine the pain threshold in 22 patients suffering from allodynia as a consequence of a chronic unilateral neuropathic pain syndrome. We performed quantitative sensory testing according to the Method of Limits protocol. We used the patient's own contralateral side and 5 healthy control participants to obtain reference values.

On the affected side, we found in 20 out of 22 patients that the pain threshold could be determined with the monofilaments. On average, these 20 patients indicated pain upon the application of monofilament with logarithmic nr. 4.56, whereas no pain threshold could be determined on the contralateral, unaffected side, and in the healthy control participants for any monofilament.

We showed that although etiology and pathophysiology of allodynia vary individually, with VFMs the clinical symptom allodynia can be quantified in a simple and practical fashion in almost all patients.