Time and frequency domain analysis of surface myoelectric signals during electrically-elicited cramps.

OBJECTIVES: To examine if different frequencies of electrical stimulation trigger different sized cramps in the abductor hallucis muscle and to analyze their surface electromyographic (EMG) behaviour in both time and frequency domains. METHODS: Fifteen subjects were studied. Stimulation trains of 150 pulses were applied to the muscle motor point. Frequency was increased (starting from 4pps with 2-pps steps) until a cramp developed. Current intensity was 30% higher than that eliciting maximal M-waves. After the first cramp ("threshold cramp"), a 30-minute rest was provided before a second cramp ("above-threshold cramp") was elicited with a frequency increased by 50% with respect to that eliciting the first cramp. RESULTS: We found greater EMG amplitude and a compression of the power spectrum for above-threshold cramps with respect to threshold cramps. M-wave changes (ranging between small decreases of M-wave amplitude to complete M-wave disappearance) occurred and progressively increased throughout stimulation trains. Significant positive correlations were found between estimates of EMG amplitude during cramps and estimated reductions of M-wave amplitude. CONCLUSIONS: Varying frequencies of electrical stimulation triggered different sized cramps. Moreover, decreases in M-wave amplitude were observed during both threshold and above-threshold stimulations. The choice of the stimulation frequency has relevance for optimizing electrical stimulation protocols for the study of muscle cramps in both healthy and pathological subjects.

A novel KCNA1 mutation identified in an Italian family affected by episodic ataxia type 1.

Episodic ataxia type 1 (EA1) is a rare human neurological syndrome characterized by continuous myokymia and attacks of generalized ataxia that can be triggered by abrupt movements, emotional stress and fatigue. An Italian family has been identified where related members displayed continuous myokymia, episodes of ataxia, attacks characterized by myokymia only, and neuromyotonia. A novel missense mutation (F414C), in the C-terminal region of the K(+) channel Kv1.1, was identified in the affected individuals. The mutant homotetrameric channels were non-functional in Xenopus laevis oocytes. In addition, heteromeric channels resulting from the co-expression of wild-type Kv1.1 and Kv1.1(F414C), or wild-type Kv1.2 and Kv1.1(F414C) subunits displayed reduced current amplitudes and altered gating properties. This indicates that the pathogenic effect of this KCNA1 mutation is likely to be related to the defective functional properties we have identified.

[Evaluation of professional exposure to chloride vinyl monomer and vinyl idene chloride for a pharmaceutical packaging worker]. / Valutazione dell'esposizione professionale a cloruro di vinile monomero e cloruro di vinilidene di un lavoratore addetto al confezionamento farmaci.

The study was conducted by Judicial Policy investigations of Prosecution's Office. The event was connected by a professional founded suspicion disease of a pharmaceutical worker. First information coming from the Authority indicated a chloride vinyl monomer (CVM) exposure. We applied a chemical risk assessment method to estimate real professional exposure. The method was based on the productive cycle, physical and chemical and toxicological properties. The method combined to environmental data permitted to formulate etiological hypothesis. The worker during drugs packaging was exposed to CVM and vinylidene chloride (CVDM) caused by blister warming and by glue deposition. We explain the evaluations by which we could consider the pollutant different distribution in workplaces.

[Biological and chemical risks in haemodialysis centres]. / Il rischio biologico e chimico in emodialisi.

Haemodialysis technique was introduced in 1965 for people afflicted to chronic renal insufficiency, permitting them to survive. The method purifies patient blood who is connected to the equipment by tubes. The equipment uses saline solutions and water and it operates by osmotic pressure and by filtration. In this paper biological and chemical occupational risks are analysed. Main biological risks are caused by haematic viruses such as HIV, HBV, HCV. Chemical risks are mainly caused by disinfection products such as acid, basic and saline solutions. Workers exposed to chemical and biological risks are nursing staff, doctors, assistants, maintenance men. The paper analyses these risks and it shows prevention and protection solutions to reduce significantly the risks. The S.Pre.S.A.L. (Prevention and Protection Service in Work Places) operators of ASL RMC (Health Local Agency of Rome) visited six haemodialysis centres situated in Rome in the ASL RMC territory. They verified the application of safety and healthy measures by use of a check list about risk assessment, the lay-out, the equipment, the preventive and protective measures and the application of law. Experimental data were organized in relation of legislative accomplishments and technical measures. The aim of our work was to improve workers' safety in the haemodialysis centres, proposing the better technical solutions to realise this objective.

Clinical features and neurophysiological follow-up in a case of Brown-Vialetto-Van Laere syndrome.

Brown-Vialetto-Van Laere syndrome is a rare disease of unknown origin commonly considered as part of the large group of motor neuron diseases. The course is quite variable: it may be quickly fatal or protracted, with relapsing phases followed by periods of arrest and even partial improvement. We describe a case of Brown-Vialetto-Van Laere syndrome with strong family history for sensorineural hearing impairment. The patient came to our medical attention for severe respiratory failure and leg weakness. The clinical conditions partially improved with recovery of spontaneous respiration and mild increase in muscle strength. The neurophysiological studies performed on our patient showed evidence of nerve damage with subsequent improvement. Our study raises the possibility that the disorder is due to primary nerve damage, which can better justify the intermittent course of the disease, the partial clinical regression and the neurophysiological improvement, never detected in typical motor neuron disorders.

Brainstem neurodegeneration correlates with clinical dysfunction in SCA1 but not in SCA2. A quantitative volumetric, diffusion and proton spectroscopy MR study.

Magnetic resonance (MR) techniques enable in vivo measurement of the atrophy of the brainstem and cerebellum in spinocerebellar ataxia type 1 (SCA1) and 2 (SCA2) patients, which is accompanied by a decrease in the concentration of N-acetyl aspartate (NAA) or of the NAA/creatine ratio in the pons and cerebellum. Mean diffusivity (D) is emerging as an additional sensitive and quantitative MR parameter to investigate brain diseases. In order to explore differences between the MR features of SCA1 and SCA2 and correlate the MR and clinical findings in the two conditions, we examined 16 SCA1 patients, 12 SCA2 patients and 20 healthy control subjects. The MR protocol included T1-weighted 3D gradient echo sequences, single-voxel proton spectroscopy of the right cerebellar hemisphere (dentate and peridentate region) and of the pons with a PRESS sequence and an external reference quantitation method, and (in nine patients with SCA1 and nine patients with SCA2) diffusion-weighted echo-planar images with reconstruction of the D maps. The patients were evaluated with the Inherited Ataxia Clinical Rating Scale (IACRS). Compared with control subjects, the SCA1 and SCA2 patients showed a decrease (P < 0.01) in the volume of the brainstem and cerebellum and in the concentration of NAA in the pons and cerebellar hemisphere, whereas D of the brainstem and cerebellum was increased. No significant difference was observed between the SCA1 and SCA2 patient groups. No correlation between cerebellar volume and dentate and peridentate NAA concentration was found in SCA1 or SCA2 patients. The volume of the brainstem, D of the brainstem and cerebellum and the concentration of NAA in the pons were correlated (P < 0.05) with the IACRS score in SCA1 but not in SCA2. This discrepancy is in line with the clinical observation that the clinical deficit has a later onset and faster progression in SCA1 and an earlier onset and slower progression in SCA2, and suggests that neurodegeneration of the brainstem is a comparatively more rapid process in SCA1. In conclusion, our study indicates that SCA1 and SCA2 substantially exhibit the same MR features. The correlation in SCA1 between clinical severity and quantitative volumetric, diffusion MRI and proton MR spectroscopy findings in the brainstem indicates that these measurements might be employed for longitudinal studies and hopefully as surrogate markers in future pharmacological trials of this condition.

Visual evoked potentials in diabetic children and adolescents.

Visual evoked potentials were studied in 30 insulin-dependent diabetic children and adolescents. Thirty percent of the subjects had evidence of significant abnormalities. No correlation was found between visual evoked potentials and age, duration of diabetes, metabolic control, and retinopathy.

Botulinum toxin treatment in the facial muscles of humans: evidence of an action in untreated near muscles by peripheral local diffusion.

In a population of subjects with blepharospasm and facial hemispasm treated for the first time with botulinum toxin type A (BT) in the orbicularis oculi muscle, we performed an electrophysiologic study (compound muscle action potential and motor evoked potential) to assess whether BT effect could be detected in near untreated muscles (orbicularis oris and masseter). There was a significant BT action in nearly untreated muscles with different peripheral innervation that can be explained by local diffusion of the drug.

Novel transthyretin missense mutation (Thr34) in an Italian family with hereditary amyloidosis.

We report on the genetic and molecular characterisation of an Italian family with a late-onset, autosomal dominant transthyretin amyloidosis. The transthyretin gene was analysed by polymerase chain reaction (PCR), restriction generating PCR, and sequencing, allowing us to discover in one allele a novel point mutation. It consists of a G to C transversion at position 1692 of the genomic sequence, leading to a Thr for Arg substitution at the position 34 of the polypeptidic chain. This mutation is associated with a severe sensory-motor peripheral neuropathy and a restrictive cardiomyopathy.

On the action of botulinum neurotoxins A and E at cholinergic terminals.

Botulinum neurotoxins type A and E (BoNT/A and /E) are metalloproteases with a unique specificity for SNAP-25 (synaptosomal-associated protein of 25 kDa), an essential protein component of the neuroexocytotic machinery. It was proposed that this specificity is based on the recognition of a nine-residue sequence, termed SNARE motif, which is common to the other two SNARE proteins: VAMP (vesicle-associated membrane protein) and syntaxin, the only known substrates of the other six clostridial neurotoxins. Here we report on recent studies which provide evidence for the involvement of the SNARE motif present in SNAP-25 in its interaction with BoNT/A and /E by following the kinetics of proteolysis of SNAP-25 mutants deleted of SNARE motifs. We show that a single copy of the motif is sufficient for BoNT/A and /E to recognise SNAP-25. While the copy of the motif proximal to the cleavage site is clearly involved in recognition, in its absence, other more distant copies of the motif are able to support proteolysis. We also report on studies of poisoning human neuromuscular junctions with either BoNT/A or BoNT/E and describe the unexpected finding that the time of recovery of function after poisoning is much shorter in the case of type E with respect to type A intoxication. These data are discussed in terms of the different sites of action of the two toxins within SNAP-25.

Different time courses of recovery after poisoning with botulinum neurotoxin serotypes A and E in humans.

Botulinum toxin serotypes A and E (BoNT/A and /E) cleave the carboxy-terminus of synaptosomal associated protein-25 (SNAP-25) removing nine and 26 residues, respectively. To investigate the effect of these lesions of the same target molecule, 11 volunteers were injected with 3 IU of BoNT/A in the extensor digitorum brevis (EDB) muscle of one foot and with 3 IU of BoNT/E in the contralateral one. In addition, seven volunteers were similarly injected with mixtures of BoNT/A + BoNT/E. Compound muscular action potential (CMAP) was measured at different time intervals and the percentage variation of CMAP (%CMAP) was calculated. Unexpectedly, a much faster recovery of %CMAP after BoNT/E injections was observed. Double poisoned EBD muscles recovered similarly to BoNT/E. So, a larger deletion of the SNAP-25 molecule caused by BoNT/E leads to a faster functional recovery.

Botulinum neurotoxin serotype C: a novel effective botulinum toxin therapy in human.

Botulinum neurotoxin (BoNT) serotype A is commonly used in the treatment of focal dystonia. Nevertheless, some patients are or become resistant to this serotype. Consequently, other different serotypes have to be used. A comparison of the neuromuscular blockade induced by BoNT type A and C in the extensor digitorum brevis muscles of voluntary subjects was studied, by evaluating the amplitude variation over the time (until 90 days) of the compound muscular action potential elicited by supramaximal electrical stimulation of the peroneal nerve at the ankle. A very similar effect and temporal profile, was observed for each serotype. On this basis, two patients with idiopathic facial hemispasm and one with blepharospasm were treated with BoNT serotype C with very beneficial long lasting effects.

Anomalous reinnervation as a sequel to obstetric brachial plexus palsy.

In 3 patients with sequelae of brachial plexus birth injury we observed associated movements and also synchronous motor unit potentials and motor axo-axonic reflexes between different muscles, sometimes with antagonist function. To explain these synkineses is necessary to assume that there is simultaneous innervation by the same motoneurone of 2 or more "motor subunits" in different muscles. Therefore we suggest that the motoneurone branches originate proximally from the primary trunk of the brachial plexus. Careful clinical and neurophysiological study can show these complex simultaneous innervations and also suggest correct kinesiotherapy.

Hypokalemic periodic paralysis. A single fiber electromyographic study.

The neurophysiological findings obtained with standard electromyography (EMG) and single fiber EMG (SFEMG) in a case of hypokalemic periodic paralysis (HoPP) are reported. During the period between paralytic attacks the only abnormalities consisted of scanty fibrillation potentials and, with SFEMG, a fiber density increase. In the first stage of an induced paralytic attack the most striking feature was decrease in fiber density, slight increase in jitter with several blocks. These results indicate a failure of the membrane surface to propagate an action potential. In some fibers the block is likely to be permanent, thus explaining the decrease in fiber density. The jitter increase is due to a slight abnormality at the synaptic site or to a variation in the propagation velocity of the muscle fiber.

Myasthenia due to carnitine treatment.

Severe weakness of lower cranial and girdle muscles has been found in 4 subjects among 20 dialysis patients treated with carnitine in order to correct their high plasma triglyceride level. Neurophysiological investigation showed an impairment of neuromuscular transmission with short-term reduction of evoked muscle responses to repetitive stimulation and the presence of "post-activation exhaustion phenomenon" 3 min after the train. Both the weakness and the neurophysiological findings were less pronounced after edrophonium. These findings suggest a hemicholinium activity of carnitine at synaptic level.

Spectrin extractability from erythrocytes in Duchenne muscular dystrophy patients and carriers and in other myopathies.

Spectrin extractability was measured in the erythrocyte membranes from patients with Duchenne Muscular Dystrophy (DMD), from DMD definite carriers (in whom serum creatine kinase (CK) was also measured) and patients affected by other myopathies. After the extraction of spectrin from ghosts with EDTA, membrane proteins were examined using sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Spectrin extractability was also investigated in the presence of an excess of calcium. Spectrin extraction from erythrocyte ghosts was significantly reduced with respect to controls in DMD patients, in DMD definite carriers and in patients affected by limb-girdle dystrophy, but not in patients suffering from other non-dystrophic myopathies. Fifty percent of DMD definite carriers showed a reduced extraction of spectrin and some of them had normal serum CK. Reduced extractability was also observed in red blood cells incubated in media containing excess calcium. Our results could suggest that reduced spectrin extractability is connected with a modification of intracellular calcium levels.

Surface mechanomyogram reflects muscle fibres twitches summation.

The aim of this work is to define the pattern of summation of the muscle fibre twitches in the surface mechanomyogram (MMG) generation process. For this purpose, two groups of muscle fibres of the extensor digitorum communis (EDC) were stimulated using needle electrodes. To these two artificial (because made by different muscle fibre types) motor units (MU1 and MU2), we administered: (a) separate stimulations: 3 and 9 Hz (MU1), 8 and 20 Hz (MU2) for 5 s; (b) simultaneous stimulation: 3 Hz (MU1) + 8 Hz (MU2); 9 Hz (MU1) + 20 Hz (MU2) for 5 s. The mechanomyograms, recorded during separate stimulation of MU1 and MU2, were linearly summated for the generation of a mechanomyographic signal to be compared with the one detected during (b) stimulation procedure. The bispectrum and the bicoherence of the generated MMG (MMGg) and of the MMG recorded during simultaneous (MMGs) stimulation were calculated for the detection of the quadratic non-linearity in the system responses. It was found that the MMGg and MMGs presented difference in the bispectrum and bicoherence index only when the 9-20 Hz stimulation pair was considered In conclusion, our data indicate that the MMG derives from the summation of the active muscle fibres twitches and that the latter is linear only for very low firing rates. This is to be carefully considered when studies on MMG modelling will be undertaken.

Spinal somatosensory evoked potentials in patients with tethered cord syndrome.

We studied the electrophysiological changes occurring in six patients with tethered cord syndrome. Evidence of spinal malformations was provided by magnetic resonance imaging. The functional assessment of the spinal cord was performed by analysing both spinal and cortical somatosensory evoked potentials. The evoked electrospinogram was recorded from the thoracic and lumbosacral spinous processes. The N22 lumbosacral potential was selectively affected, being rostrocaudally displaced and reduced in amplitude or even absent in patients with neurological signs indicating a segmental lower cord lesion. Inter-peak somatosensory evoked potentials latency was normal in all cases, suggesting that ascending axonal potentials in the dorsal column fibres may be synchronized. Segmental potentials of the lumbosacral response, originating from the post-synaptic activity of dorsal horn interneurons, are selectively affected in this syndrome resulting from the rostrocaudal displacement of the spinal cord due to tethering. Our findings in the clinical field are consistent with previous experimental evidence indicating a different sensitivity of the gray vs. white matter to progressive stretching.

Lower-limb lengthening in short stature. An electrophysiological and clinical assessment of peripheral nerve function.

We assessed peripheral nerve function during and after lower-limb lengthening by callotasis in 14 patients with short stature, using motor conduction studies. Four patients with short stature of varying aetiology showed unilateral and one showed bilateral weakness of foot dorsiflexion. Both clinical and electrophysiological abnormalities consistent with involvement of the peroneal nerve were observed early after starting tibial callotasis. There was some progressive electrophysiological improvement despite continued bone distraction, but two patients with Turner's syndrome had incomplete recovery. A greater percentage increase in tibial length did not correspond to a higher rate of peroneal nerve palsy. The function of the posterior leg muscles and the conduction velocity of the posterior tibial nerve were normal throughout the monitoring period. The F-wave response showed a longer latency at the end of the bone distraction than in basal conditions; this is probably related to the slowing of conduction throughout the entire length of the nerve.