A relationship between bruxism and orofacial-dystonia? A trigeminal electrophysiological approach in a case report of pineal cavernoma.

BACKGROUND: In some clinical cases, bruxism may be correlated to central nervous system hyperexcitability, suggesting that bruxism may represent a subclinical form of dystonia. To examine this hypothesis, we performed an electrophysiological evaluation of the excitability of the trigeminal nervous system in a patient affected by pineal cavernoma with pain symptoms in the orofacial region and pronounced bruxism. METHODS: Electrophysiological studies included bilateral electrical transcranial stimulation of the trigeminal roots, analysis of the jaw jerk reflex, recovery cycle of masseter inhibitory reflex, and a magnetic resonance imaging study of the brain. RESULTS: The neuromuscular responses of the left- and right-side bilateral trigeminal motor potentials showed a high degree of symmetry in latency (1.92 ms and 1.96 ms, respectively) and amplitude (11 mV and 11.4 mV, respectively), whereas the jaw jerk reflex amplitude of the right and left masseters was 5.1 mV and 8.9 mV, respectively. The test stimulus for the recovery cycle of masseter inhibitory reflex evoked both silent periods at an interstimulus interval of 150 ms. The duration of the second silent period evoked by the test stimulus was 61 ms and 54 ms on the right and left masseters, respectively, which was greater than that evoked by the conditioning stimulus (39 ms and 35 ms, respectively). CONCLUSIONS: We found evidence of activation and peripheral sensitization of the nociceptive fibers, the primary and secondary nociceptive neurons in the central nervous system, and the endogenous pain control systems (including both the inhibitory and facilitatory processes), in the tested subject. These data suggest that bruxism and central orofacial pain can coexist, but are two independent symptoms, which may explain why numerous experimental and clinical studies fail to reach unequivocal conclusions.

Primary motor cortex hyperexcitability in Fabry's disease.

OBJECTIVE: Involvement of pyramidal cells and/or changes in excitability of brain areas remote from an ischemic stroke has been demonstrated. Since in Fabry disease (FD), specific cerebrovascular lesions are present, we thought to investigate motor cortex excitability, using transcranial magnetic stimulation. METHODS: Resting (RMT) and active (AMT) motor threshold, input-output curve (IN-OUT), central motor conduction time (CMCT), cortical silent period (cSP), short and long interval intracortical inhibition (SICI and LICI), intracortical facilitation (ICF), short interval intracortical facilitation (SICF) and short afferent inhibition (SAI) were measured in the cortical representation of the right first dorsal interosseous muscle in 11 patients with FD and 11 sex- and age matched healthy subjects. RESULTS: FD patients showed a significant increase of steepness in IN-OUT, ICF and SICF curves. RMT, AMT, CMCT, SICI, LICI and SAI were normal. CONCLUSIONS: Our data documented an increased activity of motor cortex glutamatergic excitatory circuits in FD, evident also in patients without brain MRI lesions. Following enzyme replacement treatment, this abnormality was partly reversed. SIGNIFICANCE: We suggest that our findings are expression of subtle "biochemical brain lesions", due to an early involvement of neurons and/or astrocytes by the cascade of pathologic events leading to brain damage in FD.

Trigeminal electrophysiology: a 2 x 2 matrix model for differential diagnosis between temporomandibular disorders and orofacial pain.

BACKGROUND: Pain due to temporomandibular disorders (TMDs) often has the same clinical symptoms and signs as other types of orofacial pain (OP). The possible presence of serious neurological and/or systemic organic pathologies makes differential diagnosis difficult, especially in early disease stages. In the present study, we performed a qualitative and quantitative electrophysiological evaluation of the neuromuscular responses of the trigeminal nervous system. Using the jaw jerk reflex (JJ) and the motor evoked potentials of the trigeminal roots ((b)R-MEPs) tests, we investigated the functional and organic responses of healthy subjects (control group) and patients with TMD symptoms (TMD group). METHOD: Thirty-three patients with temporomandibular disorder (TMD) symptoms and 36 control subjects underwent two electromyographic (EMG) tests: the jaw jerk reflex test and the motor evoked potentials of the trigeminal roots test using bilateral electrical transcranial stimulation. The mean, standard deviation, median, minimum, and maximum values were computed for the EMG absolute values. The ratio between the EMG values obtained on each side was always computed with the reference side as the numerator. For the TMD group, this side was identified as the painful side (pain side), while for the control group this was taken as the non-preferred masticatory side (non-preferred side). The 5th, 10th, 25th, 50th, 75th, 90th, and 95th percentiles were also calculated. RESULTS: Analysis of the ratios (expressed as percentages) between the values obtained on both sides revealed a high degree of symmetry in the (b)R-MEPs % in the control (0.93 +/- 0.12%) and TMD (0.91 +/- 0.22%) groups. This symmetry indicated organic integrity of the trigeminal root motor fibers and correct electrode arrangement. A degree of asymmetry of the jaw jerk's amplitude between sides (ipJJ%), when the mandible was kept in the intercuspal position, was found in the TMD group (0.24% +/- 0.14%) with a statistically significant difference in relation to the control group (0.61% +/- 0.2%). This asymmetry seemed to be primarily due to a failure to facilitate the reflex on the painful side in intercuspal position. CONCLUSIONS: In this 2 x 2 matrix diagnostic model, three different types of headache may be identified: 1) those due to organic pathologies directly and indirectly involving the trigeminal nervous system denoted as "Organic Damage"; 2) those in TMD patients; 3) other types of orofacial pain in subjects who could erroneously be considered healthy, denoted as Orofacial Pain "OP". This category of patient should be considered at risk, as organic neurological pathologies could be present and yet not directly affect the trigeminal system, at least in the early stages of the disease.

Prevalence of primary blepharospasm in Sardinia, Italy: a service-based survey.

We performed a service-based epidemiological study of primary blepharospasm in the island of Sardinia (Italy). Due to its favorable geographical location, we are confident we will provide reliable data from patients seeking botulinum toxin treatment. A total of 53 patients were assessed. Prevalence was estimated to be 32.2 per 1 million (95% confidence interval, 23.0-40.8). These results are in line with those obtained in other similar surveys, that is, record-based, and performed in various European regions such as Northern England, the Munich area, as well as the Epidemiologic Study of Dystonia in Europe.

Asterixis and toxic encephalopathy induced by gabapentin.

PURPOSE: To date, only one case of asterixis associated with the use of gabapentin (GBT) has been reported. No data, instead, are available on the occurrence of asterixis related to a dementing encephalopathy during GBT therapy in the elderly. METHODS: Case reports of two elderly patients, one with asterixis, the other with asterixis and encephalopathy, associated with the use of GBT, as adjunctive therapy, at dosages of 900 to 3600 mg/day are given. In one patient, GBT was added to oxcarbazepine (OXCBZ). FINDINGS: Both patients experienced resolution of the clinically apparent asterixis, and of the toxic encephalopathy, on discontinuation or reduction of GBT dosages. One patient developed asterixis after drug rechallenge. In the patient on OXCBZ, the analysis of the electromyogram (EMG) activity showed the occurrence of a subclinical asterixis. CONCLUSIONS: Our study indicates that high doses of GBT may induce asterixis related to a reversible encephalopathy. Low doses of GBT, instead, may induce a disabling asterixis when given in combination with OXCBZ because of a synergistic interaction between these drugs.

Effects of topiramate in patients with cerebellar tremor.

PURPOSE: To evaluate the safety and potential beneficial effect of topiramate (TPM) as monotherapy or adjunctive therapy to carbamazepine (CBZ) in patients with cerebellar tremor. METHODS: Nine patients with cerebellar tremor participated a 4-week, open-label, prospective-controlled trial. TPM was given as monotherapy (n=7 cases), or in combination with CBZ (n=2 cases), at dosages ranging from 25 mg twice daily to 100 mg twice daily. The severity of tremor was assessed clinically on a 0-4 scale, by tremograms, by the Patients Global Impressions Scale, and by a "free writing" task at baseline and after 4 weeks. RESULTS: TPM was discontinued in four patients due to adverse effects (sedation=2; cognitive impairment=2; increased aggressiveness=2; asthenia=1). During TPM, all patients improved. The mean tremor amplitude, compared with the baseline period, was reduced from 20% to 75%. After TPM, mean clinical scores of postural tremor and kinetic tremor decreased from 2.1+/-0.8 to 0.9+/-0.9 and from 2.1+/-1 to 1.4+/-1 (P<.05), respectively. All patients with head tremor improved. Writing, eating, and drawing were improved with TPM. Four patients chose to keep taking the drug. CONCLUSIONS: Our study indicates that TPM may be useful for the management of cerebellar tremors. A prospective placebo-controlled trial of TPM in this kind of tremor is warranted. TPM dosages should be titrated slowly to avoid the potential side effects of the drug. The range and the frequency of adverse events might limit the clinical usefulness of TPM.

Modulation of masseter exteroceptive suppression by non-nociceptive upper limb afferent activation in humans.

The effects induced by non-noxious electrical stimulation of upper limb nerves on exteroceptive suppression (ES) of masseter muscle EMG activity were studied in 15 healthy subjects. EMG activity of masseter muscles was recorded bilaterally and great care was taken to minimise the activation of afferents other than the stimulated ones. Masseter ES was elicited by applying a non-noxious electrical stimulus to the skin above the mental nerve (Mt) of one side, during a voluntary contraction of masseter muscles at a prescribed steady clenching level. Onset and offset latencies and duration of early and late components of masseter ES (ES1 and ES2, respectively) were evaluated in control conditions and compared to those obtained when a non-noxious electrical stimulation was delivered separately to Med or Rad or simultaneously to both nerves (Med-Rad) of one side. Upper limb nerve stimulation could be simultaneous or it could precede or follow Mt stimulation by various time intervals. In control conditions, ES1 latency onset and duration values (mean +/- SD) were 11.3+/-2.9 ms and 16.9+/-2.1 ms, respectively, and ES2 latency onset and duration values were 44.5+/-6.0 ms and 28.6+/-11.1 ms, respectively. No significant differences were observed which were related to the side being recorded. Two types of effects, opposite in nature, were shown on masseter ES, depending on the time intervals between Mt and upper limb nerve stimulation. The first effect, which was facilitatory, consisted of a significant increase in ES1 and ES2 duration. A maximal increase in ES1 duration (134-155% compared to control value) occurred when upper limb nerve stimulation preceded that of Mt by 18-30 ms. Maximal ES2 lengthening (115-145%) was observed when upper limb nerve stimulation followed that of the Mt by 10 ms. The second effect was inhibitory and affected only ES2, which appeared completely eliminated when Med stimulation preceded that of Mt by 40-80 ms. By contrast, ES1 was never suppressed at any interstimulus interval. These data might reflect the different action of the central outflow, following the upper limb-induced effects, on the different neuronal circuits mediating ES1 and ES2.

Non-nociceptive upper limb afferents modulate masseter muscle EMG activity in man.

Recent electrophysiological data obtained in anaesthetized rats evidenced jaw muscle excitatory responses to the electrical stimulation of type II limb somatosensory afferents. In the present work, we describe an inhibitory reflex evoked in human masseter muscles by stimulation of non-nociceptive fibres travelling in the median and radial nerves (MED and RAD, respectively). Eighteen healthy volunteers participated in the study. Subjects were seated on a comfortable chair, with the complex head-mandible-neck-trunk and the limbs securely fixed to the chair. Attempts were made to minimize possible interferences due to the activation of afferents other than the stimulated ones. The subjects were instructed to contract masseter muscles at a submaximal level and to maintain a stable level of muscle contraction during all trials. EMG voluntary activity was recorded from both masseter muscles by means of coaxial needle electrodes before and after the electrical stimulation of MED and/or RAD at intensities below pain threshold. In all subjects, MED stimulation induced bilaterally a marked depression of masseter EMG activity, which occurred at a latency of 23.6 +/- 2.1 ms and lasted 27.8 +/- 6.6 ms. RAD stimulation also induced a marked reduction in masseter EMG activity, but this effect was clearly observed in 9 out of 18 subjects, and it showed latency (30.2 +/- 7.5 ms) and duration (44.9 +/- 5.4 ms) significantly longer in comparison with the MED-induced effect. All subjects exhibited the inhibitory period in masseter EMG following the simultaneous stimulation of both nerves; this one appeared at a latency not significantly different (25.3 +/- 5.9 ms) and lasted much more (37.4 +/ - 8.2 ms) than EMG depression evoked by MED stimulation. The duration of masseter muscle inhibition, induced by MED and/or RAD stimulation, was inversely related to the level of EMG activity, while latency was not related to it. Significant increases in the inhibitory period duration were also observed by increasing stimulus intensity, within a subthreshold range for the activation of nociceptive fibres. In all cases, the inhibitory period was followed by a later excitatory rebound activity, whose latency and duration depended on the duration of the preceding EMG inhibition and on the background level of masseter activation. In conclusion, results evidenced that the activation of arm somatosensory fibres modulates masseter muscle activity in normal man. This might lead to a coordination between limb and masticatory muscle activity, which is required in several complex motor acts.