Somatosensory evoked potentials of brain in episodic tension type headache

Aida A.Yakupova, Radik A.Yakupov, Maksum F.Ismagilov Department of neurology.

State Medical University
Kazan, Russia Background and Objectives: Significance of the central structures of the nervous system which participate in the nociceptive information processing, still remains to be solved in episodic tension-type headache. The aim of the present investigation was to study the peculiarities of somatosensory evoked potentials (SEPs) in episodic tension-type headache. Materials&Methods: 25 patients (21 females, 4 males, mean age 35 y. ± 11 s.d) with the episodic tension headache were examined. Diagnosis was performed on the basis of clinical features and electromyographic investigation of bioelectrical activity. The control group consisted of 15 healthy subjects which did not differ statistically from the experimental group by age and sex. The investigations were conducted before and after the course of treatment which included medications and methods of acupuncture therapy. Methods of investigation included: clinical neurological examination; personal assesment of pain with the use of the visual — analogous scale (from 1 to 10 points); neuropsychological testing by MMPI; electromyography of the scalp and neck muscles; the blink reflex was recorded from the orbicularic oculi muscle. The supraorbital nerve was electrically stimulated (frequency 0,1 Hz, pulse duration 1 ms, pulse amplitude 5 — 7 mA); SEPs were recorded with the position of active electrode 70-80 mm to the side from the sagittal line of head on the line which connected the point 10-20 mm backward from vertex and the external acoustic meatus, it was corresponded to the sensory projection region of the hand. Referent electrode was placed on the ipsilateral ear lobe. The stimulation electrode was situated on the median nerve projection in the lower third of the contralateral forearm. The rectangular impulses (duration 0,5 ms, intensity 8-15 mA, frequency from 0,5 Hz to 1,5 Hz with random succession) were applied. 100-120 responses were averaged for each side of stimulation. An analysis epoch 200 ms was used for selection of the early components (P1N1, P2N2) with latency up to 100 ms. Registration of the late components (P3N3, P4N4) with latency more than 100 ms was conducted by means a 600 ms analysis epoch. Amplitude (mV) and latency (ms) of the SEPs components were analysed. Capacity index (m Vґ ms) was applied for quantitative analysis of the SEPs late components (P3N3, P4N4). It was calculated as an area under the SEPs curve at the interval of 100-600 ms (fig.1). Fig.1 The SEPs parameters (capacity index for the late components is shoun by shading). Results: Initially, in acute stage of headache before treatment, the following results were obtained: Usually, the headache syndrome was characterized as monotonous, bilateral with А localization in the fronto-temporal, parieto-occipital areas or as generalizing. Pain intensity was estimated as moderate for most patients and varied from 3 to 6 points according to the visual — analogous scale. Pain did not exacerbate in physical activity and alteration of the head and body posture. Psychological status could be determined as a depressive-hypochondriac syndrome or anxious-hypochondriac syndrome on the background of the actual personal accentuations with the prevalence of anxious-hypochondriac type and tendency to the difficulty for interpersonal contacts. Bioelectrical activity in the rest for the frontal part of the epicranial muscle was recorded bilaterally without statistically significant difference of both sides in average 46,3 m V ± 15 s.d.. Investigation of the blink reflex revealed the statistically significant changes for the following parameters: the bilaterally decrease of the early component (R1) threshold and the late component (R2) threshold, the increase of the R1 amplitude and the average R2 amplitude, as well as, the R2 latency shortening and the R2 duration lengthening. Parameters of the SEPs early components (latency < 100 ms) for the episodic tension-type headache patients did not differ from the normal values. A tendency of the amplitude and duration increase was revealed for the SEPs late components (latency > 100 ms). Statistically reliable difference was established for capacity index (p<0,05). Its magnitude exceeded 420 mVx ms in 11 patients (fig 2, fig 3). Fig.2 The SEPs in the experimental group. Fig.3 The SEPs in the control group. Positive correlations were established between four variables: capacity index for the SEPs late components, pain intensity, magnitude of the MMPI scale «2» (anxiety-depression), and the late component duration of the blink reflex. In dynamics, after the treatment, the regression of the clinical symptomatology was observed, specifically, the personal assessment of pain according to data of the visual-analogous scale, relief of the main psychoemotional syndromes. At the same time, despite the tendency to normalisation, the blink reflex parameters showed the statistically significant difference in comparison with the healthy persons. After treatment the difference between experimental and control groups was insignificant but the tendency to prevalence of capacity index for the experimental group was observed. Conclusions: Certain peculiarities of reactivity for the central parts of the sensory analysator exist. Their essence consist in generalization of information about the peripheral nociceptive impulse along the vast associative areas of the cerebral cortex. Data specified can characterize one of the central factors in the mechanism of the tension-type headache development. The SEPs parameters in the complex with other tests can be used as a test of diagnosis for the evaluating the degree and dynamics of pathological process

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