Assessment of reorganization in the sensorimotor cortex after upper limb amputation.

OBJECTIVE: We wanted to investigate plastic changes occurring in the motor and somatosensory cortex after upper limb amputation, and their possible relationship to phantom pain. METHOD: To assess these plastic changes, we used transcranial magnetic stimulation (TMS) and source localization of somatosensory evoked potentials (SEP). Eleven patients with upper limb amputation were investigated. The phantom pain intensity was assessed by visual analogue scaling (VAS). RESULTS: Using TMS mapping, we found a significant lateralization of the amplitude-weighted centre of gravity (P<0.01) and an enlargement of the excitable area (P<0.05) on the hemisphere contralateral to the amputation. SEP mapping showed a significant medialization of the N20 dipole (P<0.05) on this side. None of these changes correlated with the phantom pain intensity. CONCLUSIONS: We conclude that after limb amputation, the relationship between plastic changes occurring in the sensorimotor cortex and phantom pain seems to be more complex than previously believed.

Changes of cortical excitability in patients with upper limb amputation.

In our study we wanted to assess motor excitability in patients with upper limb amputation by means of transcranial magnetic stimulation (TMS). In 12 patients, TMS was applied using a paired pulse paradigm in order to test cortico-cortical excitability. Additional parameters of motor excitability like motor threshold and cortical silent period were also measured. Recordings from the amputated side were compared to the contralateral side and to healthy controls. We found a significant reduction of intracortical inhibition in forearm amputees and an enhancement of intracortical facilitation in upper arm amputees on the affected side. We conclude that after upper limb amputation, changes in the activity of intracortical interneuronal circuits appear in the affected hemisphere. These changes may depend on the level of amputation, and be the base of cortical reorganization.

Riluzole suppresses motor cortex facilitation in correlation to its plasma level. A study using transcranial magnetic stimulation.

The aim of our study was to measure the effects of the glutamate antagonist riluzole on different parameters of motor excitability, using transcranial magnetic stimulation (TMS) during 7 days of riluzole administration, and to correlate these effects with riluzole plasma levels. Nine healthy volunteers received a dose of 100 mg riluzole from day 1 to 7 of the study period. Electrophysiological examinations were performed on day 1 before and 2 h, 5 h and 8 h after riluzole administration, on day 2, day 3 and day 5 before riluzole administration, and on day 8. Plasma samples were taken simultaneously. The excitability of the motor cortex, supraspinal and spinal motor pathways was tested by studying intracortical facilitation and inhibition, the cortical silent period and motor threshold after TMS, as well as the peripheral silent period and F-wave amplitudes after electrical peripheral nerve stimulation. We found a significant reduction of intracortical facilitation, which correlated significantly with riluzole plasma levels. To a lesser extent, intracortical inhibition was enhanced on day 1, motor threshold was increased on day 8 and F-wave amplitudes were reduced. These changes did not correlate with riluzole plasma levels. We conclude that the main effect of riluzole in vivo is a reduction of intracortical facilitation, which is closely related to the drug's level in the plasma. The most probable mechanism involves an effect on glutamatergic synaptic transmission.

Influence of the N-methyl-D-aspartate antagonist memantine on human motor cortex excitability.

The aim of our study was to investigate the effect of the N-methyl-D-aspartate (NMDA) antagonist memantine on motor excitability in humans. Seven healthy volunteers received memantine or placebo, respectively, over a period of 8 days. At day 8, transcranial magnetic stimulation (TMS) was performed using a paired pulses paradigm in order to assess intracortical inhibition and facilitation. Additionally, motor threshold and silent period duration after TMS were measured as well as M waves, F waves and peripheral silent period after electrical peripheral nerve stimulation. Intracortical inhibition was enhanced, and intracortical facilitation reduced after memantine ingestion in comparison to placebo, whereas no significant difference could be observed regarding the other neurophysiological parameters. We conclude that the NMDA receptor is involved in the regulation of excitability of intracortical interneuronal circuits.

Hemisensory impairment in patients with complex regional pain syndrome.

The purpose of the present study was to investigate the extent and quality of sensory impairment and their relation to pain characteristics and movement disorders in patients suffering from complex regional pain syndrome (CRPS) type I. Neurological testing was performed independently by two examiners in 24 patients with CRPS type I. In eight patients (33%), a hemisensory impairment with decreased temperature and pinprick sensation ipsilateral to the limb affected by CRPS could be observed. In four patients (17%), a sensory deficit in the upper quadrant of the body could be demonstrated and in eight patients (33%), sensory impairment was limited to the limb affected by CRPS. Mechanical allodynia and mechanical hyperalgesia could be observed in a higher percentage of patients with hemisensory deficit or sensory impairment in the upper quadrant (92%), than in those patients with sensory impairment limited to the affected limb (17%) (P < 0.005). In patients with left-sided CRPS, sensory abnormalities in the upper quadrant or hemisensory impairment were more frequently demonstrated (77%) than in patients with right-sided CRPS (18%) (P < 0.005). There was a high correlation (92%) for the sensory findings between the two examiners, and hemisensory abnormalities were stable over a period of 3-6 months in all six patients with repeated examinations. Motor impairment (contractures, weakness, tremor or difficulties in initiating movement) could be observed in a higher percentage in patients with sensory abnormalities in the upper quadrant or hemisensory impairment (83%) than in patients with sensory impairment limited to the affected limb (42%) (P < 0.05) and was significantly correlated with allodynia/hyperalgesia (P < 0.005). The results demonstrated that sensory deficits in patients with CRPS, frequently extend past the painful area of the affected limb. The increased frequency of mechanical allodynia and movement disorders in patients with hemisensory impairment or sensory deficits in the upper quadrant, might indicate that central mechanisms are involved in the pathogenesis of CRPS in these patients.

[Postdural puncture headache: diagnosis, prevention and therapy]. / Postpunktioneller Kopfschmerz.Diagnose, Prophylaxe und Therapie.

Lumbar puncture (LP) is a routine technique performed for a variety of procedures, e.g. diagnosis, administration of drugs, myelography and spinal anaesthesia. Postdural puncture headache is a common complication (30-40% in diagnostic LP). Prevention can be accomplished by using small-gauge needles (< or = 25 G) or pencil-point needles (22 G). Therapy should be carried out in a stepwise approach. The first step is bedrest, use of analgetics, i.v. fluids and an adequate guidance of the patient. The second step comprises special drug therapy. Several methods of pharmacologic management have been presented in the literature, but most of these are case reports. There is a lack of large double-blind placebo-controlled studies. Theophylline, caffeine, ACTH and sumatriptan are potentially promising agents for the treatment of postdural puncture headache. The efficacy of theophylline has been proven in a double-blind and placebo-controlled study. There are a few studies and case reports reporting that caffeine p.o. and i.v. is effective in the treatment of postdural puncture headache, but recurrence of headache after caffeine therapy is frequent. ACTH acts on a complex hormonal system. The treatment with sumatriptan has been reported in only a few case reports. The third step, and one of the most effective treatments of postdural puncture headache, is the epidural blood patch. The success rate ranges between 80 and 97%.