Pain-motor integration in the primary motor cortex in Parkinson's disease

In Parkinson's disease (PD), the influence of chronic pain on motor features has never been investigated. We have recently designed a technique that combines nociceptive system activation by laser stimuli and primary motor cortex (M1) activation through transcranial magnetic stimulation (TMS), in a laser-paired associative stimulation design (Laser-PAS). In controls, Laser-PAS induces long-term changes in motor evoked potentials reflecting M1 long-term potentiation-like plasticity, arising from pain-motor integration

Iatrogenic damage to the mandibular nerves as assessed by the masseter inhibitory reflex

Iatrogenic injury of the inferior alveolar or lingual nerves frequently leads to legal actions for damage and compensation for personal suffering. The masseter inhibitory reflex (MIR) is the most used neurophysiological tool for the functional assessment of the trigeminal mandibular division. Aiming at measuring the MIR sensitivity and specificity, we recorded this reflex after mental and tongue stimulations in a controlled, blinded study in 160 consecutive patients with sensory disturbances following dental procedures. The MIR latency was longer on the affected than the contralateral side (P < 0.0001). The overall specificity and sensitivity were 99 and 51%. Our findings indicate that MIR testing, showing an almost absolute specificity, reliably demonstrates nerve damage beyond doubt, whereas the relatively low sensitivity makes the finding of a normal MIR by no means sufficient to exclude nerve damage. Probably, the dysfunction of a small number of nerve fibres, insufficient to produce a MIR abnormality, may still engender important sensory disturbances. We propose that MIR testing, when used for legal purposes, be considered reliable in one direction only, i.e. abnormality does prove nerve damage, normality does not disprove it

Diagnostic accuracy of trigeminal reflex testing in trigeminal neuralgia

The authors prospectively studied 120 consecutive patients with trigeminal neuralgia (TN) to identify the clinical and laboratory features that most accurately distinguished symptomatic from classic TN. After a standardized evaluation, they identified 24 patients with symptomatic TN. Age, sensory examination, and affected division were not useful in the differential diagnosis. In contrast, electrophysiologic testing of trigeminal reflexes accurately distinguished symptomatic from classic TN (sensitivity 96%, specificity 93%)

Diagnostic accuracy of trigeminal reflex testing in trigeminal neuralgia.

[IF: 5.97] The authors prospectively studied 120 consecutive patients with trigeminal neuralgia (TN) to identify the clinical and laboratory features that most accurately distinguished symptomatic from classic TN. After a standardized evaluation, they identified 24 patients with symptomatic TN. Age, sensory examination, and affected division were not useful in the differential diagnosis. In contrast, electrophysiologic testing of trigeminal reflexes accurately distinguished symptomatic from classic TN (sensitivity 96%, specificity 93%)

Effect of pinching-evoked pain on jaw-stretch reflexes and exteroceptive suppression periods in healthy subjects

Objective: To investigate the influence of conditioning cutaneous nociceptive inputs by a new "pinch" model on the jaw-stretch reflex and the exteroceptive suppression periods (ES1 and ES2) in jaw muscles. Methods: The jaw-stretch reflex was evoked with the use of a custom-made muscle stretcher and electrical stimuli were used to evoke an early and late exteroceptive suppression period (ES1 and ES2) in the jaw-closing muscles. Electromyographic (EMG) activity was recorded bilaterally from the masseter and temporalis muscles. These brainstem reflexes were recorded in 19 healthy men (28.8 +/- 1.1 years) during three different conditions: one painful clip applied to the earlobe; one painful clip applied to the nostril, and four painful clips applied simultaneously to the earlobe, nostril, eyebrow, and lower lip. Pain intensity induced by the application of the clips was scored continuously by the subjects on a 100 mm visual analogue scale (VAS). Results: The highest VAS pain scores were evoked by placement of four clips (79 +/- 0.5 mm). There was no significant modulation of the jaw-stretch reflex (ANOVAs: P = 0.929), the ES1 (P = 0.298) or ES2 (P = 0.082) in any of the three painful conditions. Conclusions: Intense and tonic cutaneous pain could be elicited by this new "pinch" pain model; however, there was no significant modulation on either excitatory or inhibitory brainstem reflex responses. Significance: The novel observation that high-intensity pinch stimuli applied to the craniofacial region fail to modulate two different brainstem reflexes is in contrast to other experimental pain studies documented facilitation of the jaw-stretch reflexes or inhibition of exteroceptive suppression periods. The clinical implication of the present findings is that only some craniofacial pain conditions could be expected to show perturbation of the brainstem reflex responses. (C) 2007 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved

Pathophysiology of pain in postherpetic neuralgia: A clinical and neurophysiological study

Postherpetic neuralgia is an exceptionally drug-resistant neuropathic pain. To investigate the pathophysiological mechanisms underlying postherpetic neuralgia we clinically investigated sensory disturbances, pains and itching, with an 11-point numerical rating scale in 41 patients with ophthalmic postherpetic neuralgia. In all the patients we recorded the blink reflex, mediated by non-nociceptive myelinated A beta-fibers, and trigeminal laser evoked potentials (LEPs) related to nociceptive myelinated A delta- and unmyelinated C-fiber activation. We also Sought possible correlations between clinical sensory disturbances and neurophysiological data. Neurophysiological testing yielded significantly abnormal responses on the affected side compared with the normal side (P < 0.001). The blink reflex delay correlated with the intensity of paroxysmal pain, whereas the A delta and C-LEP amplitude reduction correlated with the intensity of constant pain (P < 0.01). Allodynia correlated with none of the neurophysiological data. Our study shows that postherpetic neuralgia impairs all sensory fiber groups. The neurophysiological-clinical correlations suggest that constant pain arises from a marked loss of nociceptive afferents, whereas paroxysmal pain is related to A beta-fiber demyelination. These findings might be useful for a better understanding of pain mechanisms in postherpetic neuralgia. (C) 2008 International Association for the Study of Pain. Published by Elsevier B.V. All rights reserved