Nerve block—A reliable diagnostic tool?

Abstract

Local anaesthetics have potent inhibitory effects on nerve transission in nociceptive nerve fibres, and are widely used to relieve cute pain. Sometimes, the pain relieving effect outlasts the duraion of the local anaesthetic blockade [1], and repeatednerve blocks ave been applied in an attempt to stop vicious cycles following hronic pain. Apart from that, reversible nerve blocks are mainly pplied as a diagnostic tool to localise peripheral pain generators. n this issue of Scandinavian Journal of Pain, Curatolo and Bogduk resent a highly relevant and learned review of diagnostic blocks 2]. Curatolo and Bogduk [2] differentiate between test blocks, diagostic andprognosticblocks: (1)A test blockdoesnotdistinguishone ource of pain from another; but serves to test if the blocked nerve s responsible formediating thepain related signals. (2) Adiagnostic lock is used to identify the anatomical structure that is suspected o be the source of pain. (3) A prognostic block testswhether a treatent will be successful or not. If the prognostic block is positive, a reatment of the primary lesion or a nerve ablation will most likely elieve the pain for a prolonged period. Peripheral nerve blocks vs neuraxial blocks and specific sympahetic blocks: Several peripheral nerves have been targeted such s the occipital, trigeminal, intercostal, ileoinguinal, genitofemoral, nd obturator nerves. These nerves are located superficially and re easy to access. Epidural and subarachnoidal injections of local naesthetics may have effects on both peripheral and central pain onditions, and they are not suitable for diagnosing more localised ain. Even peripheral nerve blocks may influence central pain conitions. Sympathetic inhibitors (guanethidine and phentolamine) nd local anaesthetics injected close to sympathetic ganglia have een used to test for sympathetically maintained pain. Chronic pain arising from spinal tissues and structures; importance f “comparative blocks”: Several spinal pain conditions are common nd often difficult to differentiate from each other. The clinical feaures overlap and the pain generatorsmay vary in the samepatient. mage guided block procedures, targeting the facet joints, or their erve supply, spinal nerves, and intervertebral discs have been escribed. To diagnose cervical zygapophysial joint pain compartive medial branch blocks are preferred [3]. The evidence level is igh (Evidence level I–II according to the modified U.S. Preventive