Topical high-concentration (40%) menthol-somatosensory profile of a human surrogate pain model.

UNLABELLED: Cold hyperalgesia is 1 of the characteristic signs in neuropathic pain. Topical application of menthol has been proposed as model to study cold hyperalgesia. The aim of this psychophysical study was to characterize the human surrogate of neuropathic pain of topical menthol application by using a standardized and validated protocol of quantitative sensory testing (QST). Additionally, we assessed the course of the signs elicited by menthol application over time. High-concentration 40% L-menthol was applied topically on hairy skin in 12 healthy subjects. Standardized psychophysical tests (QST) assessing 13 parameters including thermal and mechanical detection and pain thresholds were obtained before and every 45 minutes after menthol removal up to 4 hours after menthol application. Menthol decreased the cold pain threshold, mechanical pain threshold, and increased the mechanical pain sensitivity in all subjects displaying cold and mechanical pinprick hyperalgesia. In all subjects, an area of secondary pinprick hyperalgesia could be determined. Within the observation time, the decreased cold pain threshold increased continuously, whereas the signs of primary and secondary pinprick hyperalgesia remained stable. The data suggest that topical 40% menthol application is a useful model for studies of cold hyperalgesia and pinprick hyperalgesia in humans. PERSPECTIVE: This study establishes the topical application of high-concentration 40% menthol as a useful stable model for studies of cold hyperalgesia and pinprick hyperalgesia in humans. The provided long-term data are important for psychophysical and pharmacological research in humans and provide us with insights on experimental cold and mechanical hyperalgesia.

Test-retest and interobserver reliability of quantitative sensory testing according to the protocol of the German Research Network on Neuropathic Pain (DFNS): a multi-centre study.

Quantitative sensory testing (QST) is an instrument to assess positive and negative sensory signs, helping to identify mechanisms underlying pathologic pain conditions. In this study, we evaluated the test-retest reliability (TR-R) and the interobserver reliability (IO-R) of QST in patients with sensory disturbances of different etiologies. In 4 centres, 60 patients (37 male and 23 female, 56.4±1.9years) with lesions or diseases of the somatosensory system were included. QST comprised 13 parameters including detection and pain thresholds for thermal and mechanical stimuli. QST was performed in the clinically most affected test area and a less or unaffected control area in a morning and an afternoon session on 2 consecutive days by examiner pairs (4 QSTs/patient). For both, TR-R and IO-R, there were high correlations (r=0.80-0.93) at the affected test area, except for wind-up ratio (TR-R: r=0.67; IO-R: r=0.56) and paradoxical heat sensations (TR-R: r=0.35; IO-R: r=0.44). Mean IO-R (r=0.83, 31% unexplained variance) was slightly lower than TR-R (r=0.86, 26% unexplained variance, P<.05); the difference in variance amounted to 5%. There were no differences between study centres. In a subgroup with an unaffected control area (n=43), reliabilities were significantly better in the test area (TR-R: r=0.86; IO-R: r=0.83) than in the control area (TR-R: r=0.79; IO-R: r=0.71, each P<.01), suggesting that disease-related systematic variance enhances reliability of QST. We conclude that standardized QST performed by trained examiners is a valuable diagnostic instrument with good test-retest and interobserver reliability within 2days. With standardized training, observer bias is much lower than random variance. Quantitative sensory testing performed by trained examiners is a valuable diagnostic instrument with good interobserver and test-retest reliability for use in patients with sensory disturbances of different etiologies to help identify mechanisms of neuropathic and non-neuropathic pain.

A case of neuropathic brachioradial pruritus caused by cervical disc herniation.

BACKGROUND: A 64-year-old woman presented to an outpatient clinic with a 2-year history of itch, burning sensation and intermittent paresthesias within the innervation territory of the sixth cervical nerve root on the right dorsal forearm. No dermatological diseases, trauma to the affected extremity or the spine, or familial pruritus were reported. INVESTIGATIONS: Dermatological examination, skin biopsy, laser Doppler imaging, neurological physical examination and cervical MRI scan. DIAGNOSIS: Brachioradial pruritus caused by cervical disc herniation. MANAGEMENT: Ventral spinal fusion with cage implantation.

Pain in oxaliplatin-induced neuropathy--sensitisation in the peripheral and central nociceptive system.

BACKGROUND: This study aimed to determine the somatosensory characteristics and pain types in patients with acute oxaliplatin-induced neuropathy and to relate this profile to the hereby detected underlying pathophysiological mechanisms. PATIENTS AND METHODS: Sixteen patients treated with oxaliplatin for cancer were characterised with neurological assessment and a standardised and validated set for quantitative sensory testing (QST). Patients were allocated to two groups depending on the presence or absence of pain symptoms of acute neuropathy. RESULTS: Comparison with normative data revealed in patients with pain symptoms a characteristic somatosensory profile of cold and mechanical hyperalgesia. Group-to-group analysis revealed additional heat hyperalgesia and warm hypoesthesia. CONCLUSION: Pain symptoms of acute oxaliplatin-induced neuropathy are related to signs of sensitisation within the peripheral (cold and heat hyperalgesia) and central nervous nociceptive system (mechanical hyperalgesia). This strengthens the rationale for treatment with anticonvulsants and antidepressants and fosters research on ion channel and receptor related mechanisms.