Dissociated secondary hyperalgesia in a subject with a large-fibre sensory neuropathy.
In the skin surrounding a site of injury, hyperalgesia develops to mechanical stimuli. Two types of secondary hyperalgesia (to light touch and punctate stimuli) have recently been differentiated, based on different durations and sizes of the area involved. We studied secondary hyperalgesia in a subject who had a loss of myelinated afferent nerve fibres below the neck that spared the A delta group. Stroking with a cotton swab was not perceived anywhere on affected skin either before or after injection of 60 micrograms of capsaicin. Thus, there was no hyperalgesia to light touch. Capsaicin injection into the volar forearm evoked normal pain and flare. A von Frey probe exerting a force of 40 mN was perceived as sharp. The sensation of sharpness was more pronounced up to 2 cm outside the flare zone for at least 16 min following the injection (tested with a 200 mN von Frey probe). Thus, hyperalgesia to punctate stimuli developed as in healthy subjects. These data support the model that hyperalgesia to light touch (allodynia) is due to sensitisation of central pain-signaling neurones to low-threshold mechanoreceptor input (A beta fibres). In contrast, punctate hyperalgesia is likely to be due to sensitisation to nociceptor input (A delta or C fibres).
Institute of Physiology, University Hospital Eppendorf, D-2000 Hamburg 20 Germany Wessex Neurological Centre, Southampton General Hospital, Southampton SO9 4XY UK Institute of Physiology and Pathophysiology, Johannes Gutenberg University Mainz, D-6500 MainzGermany.
Rolf-Detlef
RD
Treede
Jonathan D
JD
Cole
D000328:Adult; D002211:Capsaicin / Q000009:adverse effects; D005071:Evoked Potentials / Q000187:drug effects; D006801:Humans; D006930:Hyperalgesia / Q000139:chemically induced / Q000209:etiology*; D017078:Laser-Doppler Flowmetry; D008297:Male; D008465:Mechanoreceptors / Q000187:drug effects / Q000503:physiopathology; D009412:Nerve Fibers / Q000187:drug effects / Q000502:physiology; D009475:Neurons, Afferent / Q000187:drug effects / Q000502:physiology; D009619:Nociceptors / Q000187:drug effects / Q000503:physiopathology; D010523:Peripheral Nervous System Diseases / Q000150:complications* / Q000503:physiopathology
D002211:Capsaicin