Lidocaine patch (5%) produces a selective, but incomplete block of Aδ and C fibers

• Published in: Pain (Amsterdam) Vol. 153; no. 2; pp. 273 - 280
• Main Authors: Krumova, Elena K., Zeller, Martina, Westermann, Andrea, Maier, Christoph
• Format: Journal Article
• Language: English
• Published: Philadelphia, PA Elsevier B.V 01.02.2012; Lippincott Williams & Wilkins, Inc; Elsevier
• Subjects: Adult; Aged; Analgesics; Anesthetics, Local - administration & dosage; Biological and medical sciences; Double-Blind Method; Female; Fundamental and applied biological sciences. Psychology; Humans; Hyperalgesia - drug therapy; Hyperalgesia - physiopathology; Lidocaine - administration & dosage; Lidocaine patch (5%); Male; Mechanism-based treatment; Medical sciences; Middle Aged; Nerve Fibers, Myelinated - drug effects; Nerve Fibers, Myelinated - physiology; Nerve Fibers, Unmyelinated - drug effects; Nerve Fibers, Unmyelinated - physiology; Neural Conduction - drug effects; Neural Conduction - physiology; Neuropathic pain; Neuropharmacology; Pain - diagnosis; Pain - drug therapy; Pain - physiopathology; Pharmacology. Drug treatments; Placebos; Quantitative sensory testing; Small-fiber block; Somesthesis and somesthetic pathways (proprioception, exteroception, nociception); interoception; electrolocation. Sensory receptors; Transdermal Patch; Treatment Outcome; Vertebrates: nervous system and sense organs; Young Adult; Mechanism-based treatment; Lidocaine patch (5%); Quantitative sensory testing; Small-fiber block; Neuropathic pain; Human; Pain sensitivity; Sensitivity disorder; Nervous system diseases; Hypoesthesia; Threshold detection; Hypoalgesia; Tactile sensitivity; Analgesic; Pain; Placebo; Detection threshold; Neurological disorder; Reliability; Lidocaine; Patch
• ISSN: 0304-3959; 1872-6623; 1872-6623
• DOI: 10.1016/j.pain.2011.08.020

Topical lidocaine (5%) induced a selective, but only partial blockade of Ad- and C-fibers of variable magnitude in healthy subjects, with significantly increased thermal detection and mechanical pain thresholds and decreased mechanical pain sensitivity. Topical lidocaine (5%) leads to sufficient pain relief in only 29%–80% of treated patients, presumably by small-fiber block. The reasons for nonresponse are unclear; it may be due to different underlying pain mechanisms or partly insufficient anesthetic effect. Using quantitative sensory testing (QST) following the protocol of the DFNS (German Research Network on Neuropathic Pain), this study aims to assess the type and extent of somatosensory changes after lidocaine application in healthy volunteers. Twenty-six healthy volunteers underwent QST on the volar forearm, including thermal and mechanical detection and pain thresholds, twice before (for baseline retest reliability) and once after 6-hour simultaneous application with lidocaine patch 5% and contralateral placebo in a double-blinded manner. Pre and post differences of QST parameters were analyzed by paired t-test (Bonferroni-corrected alpha 0.0023). QST profiles did not change between the 2 baseline measurements and after the placebo application. Lidocaine application led to a significant change of only the small-fiber-associated thresholds (increase of thermal detection and mechanical pain thresholds, decrease of mechanical pain sensitivity). Tactile detection thresholds representing Aβ function remained unchanged. Interindividually, the extent of the small-fiber block varied widely (eg, thermal detection thresholds: in 54% of the subjects there were only minimal changes; in only 8% were there changes of >60% of the maximal achievable value). Topical lidocaine (5%) induces thermal hypoesthesia and pinprick hypoalgesia, suggesting an isolated but only partial block of Aδ and C fibers of unpredictable extent. Further studies must analyze the influencing factors and determine whether patients with poor analgesic effect, in particular, are those with insufficient small-fiber block.