Secondary tactile hypoesthesia: a novel type of pain-induced somatosensory plasticity in human subjects.
Quantitative sensory testing revealed that pain induced by intracutaneous capsaicin injection elicited secondary hyperalgesia coexisting with secondary tactile hypoesthesia. Mapping the areas of altered mechanical sensations adjacent to the capsaicin injection disclosed that the area of secondary hyperalgesia was always nested in a larger area of secondary hypoesthesia easily detected as numbness by most subjects. Psychometric functions revealed a twofold rightward shift of tactile detection (hypoesthesia), which coexisted with a more than fourfold leftward shift of pricking pain detection (hyperalgesia) in the same skin area. As a mechanism we propose a functional switch at the spinal level based on C-fibre-induced primary afferent depolarisation resulting in presynaptic inhibition of low threshold mechanoreceptor input and an ensuing loss of tactile sensitivity.
Magerl
Walter
W
Institute of Physiology and Pathophysiology, Johannes Gutenberg-University, Saarstrasse 21, D-55099 Mainz, Germany. magerl@uni-mainz.de
Treede
Rolf-Detlef
RD
D000293:Adolescent; D000328:Adult; D000344:Afferent Pathways / Q000187:drug effects / Q000502:physiology; D002211:Capsaicin / Q000494:pharmacology; D005260:Female; D006801:Humans; D006987:Hypesthesia / Q000139:chemically induced / Q000503:physiopathology*; D008297:Male; D008465:Mechanoreceptors / Q000187:drug effects / Q000502:physiology*; D008875:Middle Aged; D036421:Nerve Fibers, Unmyelinated / Q000187:drug effects / Q000502:physiology; D009433:Neural Inhibition / Q000187:drug effects / Q000502:physiology; D009473:Neuronal Plasticity / Q000187:drug effects / Q000502:physiology; D009475:Neurons, Afferent / Q000187:drug effects / Q000502:physiology; D009619:Nociceptors / Q000187:drug effects / Q000502:physiology*; D010146:Pain / Q000139:chemically induced / Q000503:physiopathology*; D010523:Peripheral Nervous System Diseases / Q000503:physiopathology; D017729:Presynaptic Terminals / Q000187:drug effects / Q000502:physiology; D012867:Skin / Q000294:innervation; D009435:Synaptic Transmission / Q000187:drug effects / Q000502:physiology; D014110:Touch / Q000187:drug effects / Q000502:physiology*
D002211:Capsaicin