NORADRENALINE-EVOKED PAIN IN NEURALGIA

We have tested the effects of cutaneous application of noradrenaline i n 35 patients presenting with neuropathic pain. Depending on the outco me of sympatholytic interventions the patients were considered to have sympathetically maintained pain (SMP; n = 25) or sympathetically inde pendent pain (SIP; n = 10). Iontophoretic application or cutaneous inj ection of noradrenaline into symptomatic skin aggravated pain and mech anical or thermal hyperalgesia in 7/25 SMP patients. Results from diff erential nerve blocks suggested that noradrenaline-induced ongoing pai n and heat hyperalgesia were signalled by unmyelinated afferents, whil e touch-evoked pain and cold hyperalgesia were signalled by myelinated afferents. In none of the remaining 18/25 SMP patients, 10 SIP patien ts or 18 normal subjects did application of noradrenaline result in an y appreciable increase of pain. A follow-up of 12 patients (initially 9 SMP, 3 SIP) after 12-16 years showed that one individual (previously SMP) was healthy, while 3 patients still suffered from SMP and 8 from SIP. pf the 5 SMP patients who had noradrenaline-induced pain at the initial examination, only 1 SMP patient still responded to noradrenali ne with pain and hyperalgesia. Three other patients had changed to SIP and 1 individual was healthy. None of these 4 and none of the 7 initi ally noradrenaline-unresponsive patients experienced pain to the norad renaline challenge at follow-up. Thus, cutaneous noradrenaline applica tion can aggravate the pain in some, but not all SMP patients. The abn ormal noradrenaline reaction can change over time as can the pain reli eving effects of sympatholytic therapy.