Cluster headache-like pain in multiple sclerosis

We describe a case with simultaneous occurrence of cluster headache-like pain and multiple sclerosis. Both neuroimaging and neurophysiology (trigeminal evoked potentials) revealed a demyelination plaque in the pons, at the trigeminal root entry zone, on the side of pain. Although that type of lesion is usually associated with trigeminal neuralgia pain, we hypothesize that in this case it may be linked with the concomitant cluster headache, possibly by activation of trigemino-vascular mechanisms.

Early scalp responses evoked by stimulation of the mental nerve in humans

In 20 subjects, we stimulated the mental nerve through needle electrodes inserted into the homonymous foramen; recording electrodes were placed on the scalp and along the jaw. Within the 1st 5 msec after the stimulus we recorded 4 constant waves, thought to reflect the afferent activity from the mandibular nerve up to the trigeminal nuclei. These waves have similar characteristics and the same high degree of reliability as those obtained after stimulation of the infraorbital and supraorbital nerves; therefore, they should be a useful complement for a complete exploration of trigeminal nerve function.

Excitability of the Adelta nociceptive pathways as assessed by the recovery cycle of laser evoked potentials in humans

To investigate the excitability of Adelta nociceptive pathways and the nature of the vertex laser evoked potentials (LEPs), we studied the recovery cycle of the P2-LEP component and compared it with that of the P200 of the somatosensory evoked potential (SEP). Using two identical CO(2)-laser stimulators, we delivered paired stimuli to two adjacent skin spots on the hand at interstimulus intervals ranging from 250 ms to 2 s. The test P2-LEP was strongly inhibited at the 250-ms interstimulus interval ( P<0.01) and progressively recovered by the 2-s interval. The P200-SEP, after paired stimuli to the median nerve, showed a time course even slower than the P2-LEP ( P<0.01). Besides providing the LEP recovery curve in normal subjects, our findings indicate that the P2-LEP relays through a number of synapses similar to (or even lower than) that for the P200-SEP, thus lending further support to the view that the nociceptive P2-LEP is not an endogenous potential equivalent to the P300.

Trigeminal neuralgia in pontine ischaemia

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New subcortical components of the cerebral somatosensory evoked potential in man

Two new components of the human SEP upon stimulation of the contralateral median nerve at the wrist have been identified. Such components have been called N16 and N17, according to their polarity and latency. N16 and N17, as well as the N14-P15 complex, are generated by separate subcortical dipoles. Particularly, they are supposed to be far-field reflections of the activity of the dorsal columns nuclei or the medial lemniscus (N14-P15), the thalamus (N16) and the thalamo-cortical radiation (N17). Moreover, it has been established that N14 is the very first intracranial component of the human SEP, the main peak of S wave and the preceding ones being extracranial in origin. A new classification of SEP intracranial components including early (N14 through N17), intermediate (N20 through P30) and late events is proposed.

Trigeminal evoked potential-monitored thermorhizotomy: a novel approach for relief of trigeminal pain

This paper presents a complete method for performing trigeminal thermorhizotomy, guided by neurophysiological data, to relieve tic douloureux. The method involves the use of trigeminal evoked potentials (TEPs) produced by stimulation of the supraorbital, infraorbital, and mental nerves and recorded from electrodes at both the scalp and the trigeminal nerve. To perform the thermorhizotomy, a cannula is modified to produce a concentric bipolar electrode that is suitable for both recording and lesion making. The operating procedure is divided into five steps: Step 1, recording of baseline scalp TEPs from the derivation of the cervical vertex to C-7 to ensure that all stimulating electrodes are correctly placed; Step 2, recording of TEPs from the trigeminal electrode after stimulation of the peripheral nerve trunks to ascertain the electrode's position relative to the root bundles; Step 3, fine positioning of the trigeminal electrode by recording the root activity evoked by stimulation of cutaneous trigger points or of the most painful areas; Step 4, assessing the position of the trigeminal electrode relative to the motor root by stimulating the nerve via the electrode and observing the masseter motor responses; and Step 5, recording scalp TEPs immediately before and after each thermolesion. Thermolesions are made until the scalp-recorded wave W2 decreases its amplitude by 20% to 50% of the original value or until it is delayed by 0.30 msec. This procedure has the potential to enable extremely precise monitoring of the position of the trigeminal electrode relative to the activated fibers and provides very effective monitoring of the extent of the lesion. The authors have performed this procedure with very satisfactory results in 30 patients with trigeminal neuralgia in the second branch.

Lowering body temperature with a cooling suit as symptomatic treatment for thermosensitive multiple sclerosis patients

A cooling system (Mark VII Microclimate System) was used to give six thermosensitive multiple sclerosis patients two 45-minute daily coolings for a period of one month. Before the first cooling, a baseline clinical and electrophysiological examination was performed. The same tests were repeated after the first application and after the thirtieth cooling day, thus providing information relating to acute and chronic efficacy. A clinical improvement was observed after both acute and, more unexpectedly, chronic cooling, whereas a significant improvement in central somatosensory conduction was recorded only under acute conditions. Our data suggest that cooling with this device leads to an improvement in some functional performances (mainly fatigue and strength) of about two hours' duration in thermosensitive patients.

Spinal components of the cerebral somatosensory evoked response in normal man: the "S wave"

Responses evoked over the scalp and the neck by median nerve (or finger I) stimulation were concurrently recorded in 10 subjects. It was found that the first component of the cortical SEP consists of a small amplitude polyphasic wave (S wave) which could be recorded bilaterally upon unilateral stimulation. The polarity of the S wave varied according to the reference electrode position, at variance with the P15 component which remained constantly positive. It is therefore correct to assume that different generators are responsible for these two potentials. The synchrony between the S wave and the cervical response, which is largely spinal in origin, as well as some pertinent experimental data, suggest that the S wave is a far field reflection of activity generated mainly in the cervical dorsal columns. These findings might be relevant to the diagnosis of neurological disorders.

Electrophysiological features of the mouse tail nerves and their changes in chemotherapy induced peripheral neuropathy (CIPN)

Electrophysiology of tail nerves in rodents has been demonstrated a reliable method to investigate models of peripheral neuropathies. Nevertheless, data concerning mouse models are lacking. We assessed the normal features of sensory and motor conduction of tail nerves in adult mice. We found that, as in rats, a sensory compound action potential and motor responses could be recorded with the non invasive and highly reliable technique proposed, especially if bipolar derivations were used. We also investigated the changes related to chemotherapy induced peripheral neuropathy (CIPN) after paclitaxel treatment (times 1 and 2), compared to pre-treatment (time 0) and to controls. It was found that only the sensory compound action potential was involved in CIPN, with decrease in amplitude and conduction velocity, suggesting a significant reduction in number of fast conducting fibres and a correspondent increase in the number of slow conducting ones, although the total amount of active myelinated fibres was deemed to be unchanged through time 0, time 1 and time 2. The results obtained in CIPN provide new functional evidence about the involvement of sensory fibres and may help in better understanding the underlying mechanisms.

Head extensor reflex evoked by trigeminal stimulation in humans

OBJECTIVE

Excitatory and inhibitory responses have been recognized in human cervical muscles following trigeminal stimulation. However, no evidence has so far been published of a crossed, short-latency, excitatory response resembling the early head extensor reflex seen in the cat. We seek its existence in humans.

METHODS

The study was carried out in 14 voluntary healthy subjects. Percutaneous and surface electrical stimulation of the supraorbital and infraorbital nerves was performed with single, double and repetitive stimuli. Signals were recorded from the relaxed splenius and sternomastoid muscles bilaterally.

RESULTS

Percutaneous stimulation of infraorbital nerve with single stimuli evoked an early response in the contralateral splenius muscle, with onset latency ranging from 11 to 14 ms (HR1). This response was greatly facilitated by double or repetitive stimuli. Single stimuli also gave rise to two larger responses in all 4 muscles in the latency ranges 50-70 ms (HR2) and 100-160 ms (HR3). Surface stimulation of one nerve alone could not elicit any early activity. Single surface stimuli delivered simultaneously to the supraorbital and infraorbital nerves evoked HR1 in only 5 subjects.

CONCLUSIONS

We detected a crossed early reflex of the head extensor muscles to trigeminal stimuli. Its timing is similar to the 8-ms response seen in cats. The evidence provided suggests that the reflex is mediated by an oligosynaptic circuit and that it needs a strong spatial summation at central synapses.

Early abnormalities in sciatic nerve function and structure in a rat model of Charcot-Marie-Tooth type 1A disease

We investigated early peripheral nervous system impairment in PMP22-transgenic rats ("CMT rat"), an established animal model for Charcot-Marie-Tooth disease 1A, at postnatal day 30 (P30), when the clinical phenotype is not yet apparent. Hemizygous CMT1A rats and wildtype littermates were studied by means of behavioral examination, electrophysiology, molecular biology, and light microscopy analysis. Behavioral studies only showed, a mild, but significant, decrease in toe spread 1-5, suggesting a weakness of distal foot muscles in CMT1A rats compared with normal littermates. Nerve conduction studies disclosed a severe slowing in motor conduction velocity, a temporal dispersion and a dramatic decrease of amplitude of motor waves in P30 transgenic animals. Coherently with a demyelinating process, affected nerves showed a significant thinning of myelin. Interestingly, axonal diameter and area were unchanged, but expression of non-phosphorylated neurofilaments was increased in CMT1A rats compared with normal controls. Our results confirm the fidelity of this animal model to human disease. Similarly, in young CMT1A patients, the MCV is significantly reduced and the muscle weakness is confined to distal segments, whereas morphological and morphometrical signs of axonal atrophy are absent. However, the presence of a molecular and functional damage of the axons suggests that this may be the correct moment to start neuroprotective therapies.

Early scalp responses evoked by stimulation of the supraorbital nerve in man

In 25 healthy volunteers the supraorbital nerve was stimulated and evoked potentials were recorded. Leads were placed on the scalp and along the ipsilateral eyebrow-mastoid line and were either referred to a non-cephalic reference (on the neck, or Cv7) or linked to form bipolar derivations. As template wave form was chosen the one obtained from derivation Cz-Cv7, which had an initial triphasic component with negative (SW1a), positive (SW1b), negative (SW1c) polarity (mean latencies 0.63, 0.95 and 1.43 msec), followed by 2 negative waves (SW2 and SW3, mean latencies of 2.20 and 2.89 msec). A final positive wave could be observed in most cases (SP4, mean latency of 4.08 msec). The records collected from the various derivations showed that each component (SW1, SW2, SW3 and SP4) had a different behaviour, thus suggesting separate origins. SW1 would originate from a volley travelling from the point of stimulation towards the mastoid, probably across the ophthalmic branch of the trigeminal nerve. The subsequent components would be generated by deeply situated structures: double pulse stimulation suggests that SW1, SW2 and SW3 are generated before the first synapse, whereas SP4 is a postsynaptic event. A strong similarity exists between the components evoked by stimulation of the supraorbital and the infraorbital nerves. Local anaesthetic block of the frontal nerve on the stimulated side and monitoring of the EMG activity of m. orbicularis oculi and m. frontalis ruled out any muscle contamination of the responses described in this paper.

Evaluation of administration of isoflurane at approximately the minimum alveolar concentration on depression of a nociceptive withdrawal reflex evoked by transcutaneous electrical stimulation in ponies

OBJECTIVE

To investigate effects of isoflurane at approximately the minimum alveolar concentration (MAC) on the nociceptive withdrawal reflex (NWR) of the forelimb of ponies as a method for quantifying anesthetic potency.

ANIMALS

7 healthy adult Shetland ponies.

PROCEDURE

Individual MAC (iMAC) for isoflurane was determined for each pony. Then, effects of isoflurane administered at 0.85, 0.95, and 1.05 iMAC on the NWR were assessed. At each concentration, the NWR threshold was defined electromyographically for the common digital extensor and deltoid muscles by stimulating the digital nerve; additional electrical stimulations (3, 5, 10, 20, 30, and 40 mA) were delivered, and the evoked activity was recorded and analyzed. After the end of anesthesia, the NWR threshold was assessed in standing ponies.

RESULTS

Mean +/- SD MAC of isoflurane was 1.0 +/- 0.2%. The NWR thresholds for both muscles increased significantly in a concentration-dependent manner during anesthesia, whereas they decreased in awake ponies. Significantly higher thresholds were found for the deltoid muscle, compared with thresholds for the common digital extensor muscle, in anesthetized ponies. At each iMAC tested, amplitudes of the reflex responses from both muscles increased as stimulus intensities increased from 3 to 40 mA. A concentration-dependent depression of evoked reflexes with reduction in slopes of the stimulus-response functions was detected.

CONCLUSIONS AND CLINICAL RELEVANCE

Anesthetic-induced changes in sensory-motor processing in ponies anesthetized with isoflurane at concentrations of approximately 1.0 MAC can be detected by assessment of NWR. This method will permit comparison of effects of inhaled anesthetics or anesthetic combinations on spinal processing in equids.

A reassessment of sensory evoked potential parameters in multiple sclerosis: a discriminant analysis approach

The sensitivity of the different parameters (absolute latency, interwave latency, latency asymmetry, amplitude) of both cervical and cerebral responses evoked by stimulation of the median nerve at the wrist was assessed in patients with multiple sclerosis by discriminant analysis. The peak latency of N13 or N20 SEP components or both was found to be more sensitive than their amplitude, provided that a preliminary covariation with the height of the subjects was performed. The measurement of latency asymmetry between the two sides increased the test's sensitivity, while amplitude asymmetry turned out to be of little diagnostic value. A linear discriminant function with four variates (that is mean amplitude, mean latency, latency asymmetry and height of the subject) was computed to summarise the information provided by the different parameters to give a rapid and exact method for the assessment of SEP abnormalities in multiple sclerosis patients.

Compound action potential of sensory tail nerves in the rat

Assessment of the conduction velocity of motor fibers of the rat tail nerves has been used by some authors in the past, but very little is known about the sensory fibers. In 10 adult rats, weighing between 320 and 380 g, responses from the nerves and muscles of the tail have been recorded after stimulation at its root and tip. It was found that stimulation of the tip involved mainly sensory fibers, of which two main groups could be identified. One faster group, conducting within the range of 38-27 m/s, and one slower group with range 14-7 m/s. The bipolar recording configuration was found to be optimal for sensory recording. Stimulation of the tail root evoked a motor response, which was preceded by a very small neurographic activity, due to the fastest sensory fibers conducting antidromically. The conduction velocity of motor fibers was calculated to be approximately 19 m/s. Distance traveled by the volley can be assessed with excellent precision on the tail nerves; hence the calculated conduction velocities are highly reliable and reproducible. We propose that the tail nerves may be a useful tool for evaluation of conduction velocity of Abeta and Adelta afferents. As the technique is just minimally invasive, the test can be repeated a number of times in animals under chronic experimental conditions.

Prévalence des sténoses des artères rénales dépistées au cours de coronarographies diagnostiques : dans quels cas doit-on réaliser une aortographie abdominale ?

PURPOSE

To define a subgroup of patients at increased risk of renal artery stenosis (RAS) in a population of patients undergoing cardiac catheterization.

MATERIALS AND METHODS

A total of 467 patients (mean age of 64 Years +/-11) underwent cardiac catheterization and aortography Results were evaluated to detect correlations between the presence or absence of RAS and clinical and biological parameters.

RESULTS

A total of 42 (9%) patients had a renal artery stenosis. Univariate analysis defined parameters correlated with the presence of RAS: systolic blood pressure (p=0.03), pulse pressure (p=0.005), age (p<0.0001), creatinine clearance (p<0.0001), 2-vessel (p=0.028) and 3-vessel (p=0.037) coronary artery diseases. Multivariate analysis showed that the presence of RAS correlated to creatinine clearance (p=0.02) and 2-vessel coronary artery disease. A creatinine clearance between 30 and 60 ml/min and multi-vessel coronary artery disease defined a subgroup at increased risk of RAS with sensitivity, specificity, positive and negative predictive values of: 47.6, 90.1, 32.3 and 94.6%. The prevalence of renal artery stenosis was 5.2% when both parameters were absent.

CONCLUSION

Patients with mild renal insufficiency and multi-vessel coronary artery disease defined a subgroup of patients at increased risk of RAS (32.5%) that may benefit from abdominal aortography performed at the time of cardiac catheterization.

Telethermographic findings after transcutaneous electrical nerve stimulation

The purpose of this study was to determine whether some types of transcutaneous electrical nerve stimulation cause local vasodilation. The amount of vascular perfusion was monitored using telethermography to gauge the skin temperature of the area to which TENS was applied. We studied the effects of four different modalities of TENS (intensities of 1.5 and 3 times the sensory threshold and frequencies of 3 pulses per second [pps] and 100 pps), delivered through small and large electrodes (1.5 cm and 4 cm in diameter), on 10 healthy subjects. Stimulation at 3 times the sensory threshold produced local hyperthermia, which was maximal when a current of 100 pps was delivered through small electrodes. Because any physical or chemical effects of the current could be eliminated as causes of hyperthermia, the rise in skin temperature was considered to be a result of increased vascular perfusion. The results of the study demonstrate that some types of TENS cause local vasodilation. This effect may represent another mechanism by which such techniques provide pain relief, particularly in the treatment of myofascial syndromes.

Migraine treatment with nicardipine

A novel calcium entry blocker, nicardipine, has been tested using a dosage of 20 mg twice a day against placebo on 30 patients suffering from migraine without aura, according to a double-blind, cross-over design; overall duration of the study was four months (two with nicardipine and two with placebo). Migraine parameters such as monthly frequency, mean intensity and mean duration of attacks were monitored. Two indexes were also calculated: index A (monthly frequency x mean intensity) and index B (monthly frequency x mean intensity x mean duration). All the parameters considered and the two indexes showed a marked and significant improvement after nicardipine treatment in comparison to both placebo and pre-study scores. Detailed analysis of the cross-over results showed that improvement obtained with nicardipine lasted some time after the drug was discontinued. Nicardipine did not alter the blood and attention tests performed and caused few side effects.

Conducted and segmental components of the somatosensory cervical response

Cervical responses evoked by stimulation of the median nerve have been concurrently recorded from C7--Fz and C7--Sn (suprasternal notch). The existence of two different waveforms (RI and RII) has been confirmed. RI (from C7--Fz) consists of four negative peaks (N9, N11, N13, N14) followed by a large positive deflection (P16). RII (from C7--Sn) is characterised by an early positive--negative spike (P1--N1a) followed by a slow negative--positive wave (N1b--P2). The study of the most relevant parameters (polarity, latency and refractory period) of each component of RI and RII did not indicate whether the generators underlying RI differ from those responsible for RII. However, stimulation of the lower limb, which does not involve segmental events at cervical level, showed a clearcut difference: no response was recorded from C7--Sn, while evoked activity equivalent to RI was obtained from C7--Fz. Therefore it is suggested that RII is entirely generated by segmentally evoked potentials while RI is mainly due to conducted potentials.

Therapy of trigeminal neuralgia secondary to multiple sclerosis

Trigeminal neuralgia occurs in approximately 1-2% of patients suffering from multiple sclerosis. Its pathophysiology is common to idiopathic forms and resides in altered properties of the sensory axonal membrane at the root entry zone into the pons, leading to parossistic firing. Antiepileptic drugs of the sodium channel blocker type, such as carbamazepine, lamotrigine, and phenytoin are highly effective in controlling pain. However, side effects on the CNS may, at higher doses, severely worsen the already impaired neurologic conditions in multiple sclerosis patients. Baclofen, a presynaptic muscle relaxant is also beneficial in trigeminal pain. Whatever the drug, habituation and loss of efficacy are likely to occur sooner or later. Symptomatic, neurolesive surgery is indicated in cases resistant or intolerant to medical therapy. Radiofrequency thermorhizotomy, either monitored by trigeminal evoked potentials or not, is the recommended procedure, as it may be considered the most reliable as far as localization and degree of lesion are concerned.

Trigeminal sensory pathway function in patients with SUNCT

OBJECTIVE

Short-lasting unilateral neuralgiform headache with conjunctival injection and tearing (SUNCT) is a rare primary headache whose origins are unclear. To seek information on its pathophysiology, we studied the trigeminal Abeta and Adelta pathways by recording trigeminal reflexes and laser evoked potentials (LEPs) in patients with SUNCT.

METHODS

Trigeminal reflexes and LEPs were recorded in 11 consecutive patients. Ten patients had neuroimaging evidence documenting idiopathic SUNCT and one had a posterior fossa tumour that compressed the trigeminal nerve thus causing symptomatic SUNCT.

RESULTS

Whereas the patients with idiopathic SUNCT had normal trigeminal reflex and LEP responses, the patient with symptomatic SUNCT had abnormal responses.

CONCLUSIONS

Our neurophysiological findings show that idiopathic SUNCT spares the trigeminal sensory pathways whereas symptomatic SUNCT does not.

SIGNIFICANCE

Neurophysiological testing can easily differentiate the idiopathic and symptomatic forms of SUNCT. It also suggests that the two forms are pathophysiologically distinct entities.