Dynamic Mechanical Allodynia Research Articles

Dynamic mechanical allodynia is not mediated by a central presynaptic interaction of aβ-mechanoceptive and nociceptive c-afferents

Dynamic mechanical allodynia is not mediated by a central presynaptic interaction of aβ-mechanoceptive and nociceptive c-afferents

A case of `pure' dynamic mechano-allodynia due to a lesion of the spinal cord: pathophysiological considerations

We report the unusual observation of a patient who presented with the single symptom of a very intense, brush-induced allodynia (dynamic mechanical allodynia) which was strictly confined to the left C2 and C3 dermatomes. All investigations, including a cervical spinal MRI, were initially normal. The clinical picture remained stable for several months until the appearance of spontaneous pain and sensory deficits suggestive of a spinal lesion. A second MRI revealed an intraspinal lesion involving the C2–C5 segments. In accordance with other clinical and animal studies, such an observation of a `pure' dynamic mechano-allodynia suggests that specific mechanisms underlie each component of neuropathic pain. Possible pathophysiological mechanisms are discussed in the light of recent experimental results obtained in animals.

Mechanical allodynia in postherpetic neuralgia: evidence for central mechanisms depending on nociceptive C-fiber degeneration.

In 12 zoster patients who had developed postherpetic neuralgia with dynamic mechanical allodynia and in six zoster patients who had recovered without pain, the functional role of nociceptive C-fibers in allodynia was assessed by quantifying axon reflex reactions induced by histamine iontophoresis within allodynic regions and in their contralateral sites. In patients with postherpetic neuralgia, histamine responses were reduced or abolished within allodynic areas, indicating degeneration of nociceptive C-fibers. In patients who recovered without pain, histamine responses were bilaterally identical, indicating complete regeneration of nociceptive C-fibers. These results demonstrate that sensitized nociceptive C-fibers are not involved in signaling and maintenance of allodynia. Alteration in CNS processing may reorganize synaptic ties between central pain-signaling pathways and mechanoreceptive A beta-fibers depending on afferent C-fiber degeneration rather than ongoing C-fiber input.

Painful Neuropathy

In neuropathic pain states, dynamic mechanical allodynia is mediated by large diameter A beta-fibers. We test whether ongoing peripheral C-nociceptor input is necessary to maintain central changes hypothetically responsible for A beta-mediated allodynia. A patient with long-standing diabetes mellitus demonstrated generalized signs of painless diabetic small fiber polyneuropathy. Following mechanical trauma, the patient additionally developed a typical neuropathic pain syndrome at the arm. Despite substantial impairment of cutaneous small fiber function, he complained of severe dynamic mechanical allodynia confined to a forearm skin area. Marstock test revealed a considerably increased cold perception threshold within the allodynic area and on the contralateral side. The patient could not perceive any warm sensation on either side. Histamine iontophoresis was not followed by any itch or pain sensations within the allodynic area or contralaterally. Nociceptive C-fiber axon reflex reactions were substantially impaired within the allodynic skin or contralaterally. Standard neurophysiological testing and quantitative vibrametry showed only mild impairment of large diameter sensory and motor fiber function at the arms. Cardiovascular reflex tests showed almost no heart rate variation indicating impairment of vagal small fiber function. (a) Cutaneous nociceptive C-fibers do not signal dynamic mechanical allodynia. This symptom may hypothetically be due to secondary changes in the central nervous system processing that might strengthen the synaptic ties between A beta-fibers and central nociceptive pathways, or due to peripheral multiplication of primary afferent low threshold mechanoreceptor input. (b) Ongoing nociceptive C-fiber input is not necessary to maintain either hypothetical mechanism. (c) Hypothetical secondary central hyperexcitability might work autonomously without any nociceptive C-fiber input for a long time or even indefinitely in some neuropathic patients.

Absorption of vitamin B12 in pernicious anaemia. I. Oral administration without a source of intrinsic factor.

Dynamic mechanical allodynia is a widespread and intractable symptom of neuropathic pain for which there is a lack of effective therapy. We recently provided a novel perspective on the mechanisms of this symptom by showing that a simple switch in trigeminal glycine synaptic inhibition can turn touch into pain by unmasking innocuous input to superficial dorsal horn nociceptive specific neurons through a local excitatory, NMDA-dependent neural circuit involving neurons expressing the gamma isoform of protein kinase C. Here, we further investigated the clinical relevance and processing of glycine disinhibition. First, we showed that glycine disinhibition with strychnine selectively induced dynamic but not static mechanical allodynia. The induced allodynia was resistant to morphine. Second, morphine did not prevent the activation of the neural circuit underlying allodynia as shown by study of Fos expression and extracellular-signal regulated kinase phosphorylation in dorsal horn neurons. Third, in contrast to intradermal capsaicin injections, light, dynamic mechanical stimuli applied under disinhibition did not produce neurokinin 1 (NK1) receptor internalization in dorsal horn neurons. Finally, light, dynamic mechanical stimuli applied under disinhibition induced Fos expression only in neurons that did not express NK1 receptor. To summarize, the selectivity and morphine resistance of the glycine-disinhibition paradigm adequately reflect the clinical characteristics of dynamic mechanical allodynia. The present findings thus reveal the involvement of a selective dorsal horn circuit in dynamic mechanical allodynia, which operates through superficial lamina nociceptive-specific neurons that do not bear NK1 receptor and provide an explanation for the differences in the pharmacological sensitivity of neuropathic pain symptoms.