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Biomedical subjects

J Machetanz

Publications and source records attributed to J Machetanz.

At least 19 recordsLinked to original sources
PubMed2001

Reorganization of human motor cortex after hand replantation.

In 10 patients, reorganizational changes of the motor cortex contralateral to a replanted hand (MCreplant) were studied one to 14 years after complete traumatic amputation and consecutive successful replantation of the hand. The organizational state of MCreplant was assessed for the deafferentated and peripherally deefferentated hand-associated motor cortex and the adjacent motor representation of the proximal arm. For this, response maps were established for the first dorsal interosseus and biceps brachii muscle using focal transcranial magnetic stimulation (TMS) on a skull surface grid. Characteristics of the maps were center of gravity (COG), number of effective stimulation sites, amplitude sum, and amplitudes and response threshold at the optimal stimulation point. The COG is defined by the spatial distribution of response amplitudes on the map and lies over the cortex region with the most excitable corticospinal neurones supplying the recorded muscle. The COG of the biceps map in MCreplant was shifted laterally by 9.8 +/- 3.6 mm (range 5.0-15.7 mm). The extension of the biceps map in MCreplant was increased and the responses were enlarged and had lowered thresholds. For the muscles of the replanted hand, the pattern of reorganization was different: Response amplitudes were enlarged but thresholds, COG, and area of the cortical response map were normal. The different reorganizational phenomena observed for the motor cortical areas supplying the replanted hand and the biceps brachii of the same arm may be influenced by a different extent of deafferentation and by their different role in hand motor control.

Adolescent↗
PubMed2001

[Pseudomigraine with pleocytosis].

We report two cases of male patients aged 32 and 34 presenting with headache, neurological deficits, and fever. Neither the patients nor their families had a history of migraine. Analysis of the CSF revealed lymphocytic pleocytosis, but no causative infectious agent could be identified. During the attacks, EEG showed focal slowing and was normal afterwards. Computed tomography, MRI, Doppler sonography, and routine blood parameters were normal. In both patients, the focal deficits and the headache vanished within a few hours. We diagnosed a pseudomigraine with pleocytosis (PMP), recently described as an entity. This disorder is characterized by brief relapsing attacks with headache, nausea, vomiting, focal neurological deficits, and a lymphocytic pleocytosis in the CSF. The differentiation from vascular disorders is important because angiography should be avoided due to a high rate of complications in patients with PMP.

Adult↗
PubMed2001

Evaluation of clinical, electrophysiologic, and computed tomographic parameters in replanted hands.

OBJECTIVE: To compare clinical, electrophysiologic, and computed tomography (CT) imaging correlates of reinnervation in replanted limbs. DESIGN: Patients were assessed between 8 and 194 months after replantation of completely severed hands. SETTING: University hospital, departments for neurology and for plastic and reconstructive surgery. PARTICIPANTS: Thirteen patients, 10 with total and 3 with subtotal type V amputation, whose hands had been reattached. INTERVENTIONS: Clinical assessment of function of hand and finger muscles; electromyographic tests of sensory nerve action potentials (SNAPs) of median, ulnar, and radial nerves; and compound motor action potentials (CMAPs) of abductor pollicis brevis, first dorsal interosseus, and abductor digiti minimi muscles. CT assessment of motor unit action potentials. Measurements of both replanted and normal hands. MAIN OUTCOME MEASURES: Medical Research Council scale of force; sensory functions of anatomic areas of nerves; SNAP and CMAP amplitudes; CT area, mean absorption, standard deviation (SD) from mean absorption, and root mean square SD of absorption. RESULTS: Correlates of reinnervation were evidenced by all methods, except by surface recordings of SNAPs, which could not be elicited even in hands with good sensory function. CMAP amplitudes were the electrophysiologic parameter that correlated best with the clinical restoration. Of the CT measures, the cross-sectional area was the most useful parameter for the detection of denervation, but no CT parameter was sufficiently sensitive to detect reinnervation. In cases with good functional recovery, CMAP amplitudes were superior to clinical rating in showing incomplete reinnervation. CONCLUSION: The combination of clinical and electrophysiologic methods supplied sufficient data for a reliable evaluation of reinnervation. Usually, CT parameters did not add useful information.

Action Potentials↗
PubMed2001

Bilateral cerebellar infarctions caused by a stenosis of a congenitally unpaired posterior inferior cerebellar artery.

Bilateral symmetrical cerebellar infarcts in the territory supplied by the medial posterior inferior cerebellar artery (PICA) branches are extremely rare. In the few cases published, it has not been possible to clearly pinpoint the cause of this infarct pattern. The authors present the case history of a 58-year-old man who had acute headaches accompanied by pronounced rotatory vertigo with nausea and vomiting. The neurological examination revealed bilateral cerebellar signs. Cranial magnetic resonance imaging showed bilateral, nearly symmetrical infarcts in the territory of the medial branches of both PICAs. These bilateral PICA infarctions were caused by a stenosis of an unpaired PICA originating from the left vertebral artery supplying both cerebellar hemispheres.

Arterial Occlusive Diseases↗
PubMed1995

Comparison of various coils used for magnetic stimulation of peripheral motor nerves: physiological considerations and consequences for diagnostic use.

We compared the ability of 4 magnetic coils to activate peripheral nerves in healthy subjects. No differences in motor threshold intensities were found between the coils, but the intensities needed to elicit maximum compound muscle action potential (CMAP) amplitudes were different. For superficial nerves maximum CMAPs in comparison with electrical stimulation were usually but not always found. CMAPs were at their maximum only when the direction of induced current flowed from proximal to distal and when a certain part of the coil was over the nerve. Distal nerve stimulation was time consuming. Due to artifacts many stimuli were necessary and sometimes no maximum CMAP could be elicited. CMAPs were much less sensitive to position changes of the coil than to changes in an electrical stimulator. Small circular coils were superior to larger coils in terms of the lower intensities necessary to elicit maximum CMAPs, better focusing of the stimulus, and less artifacts. For deep nerves amplitudes were always submaximal. Coactivation of nearby nerves and underlying muscles was another main drawback especially at proximal sites and for coils of large diameter. Despite better focusing, double coils are less useful due to their great diameter. Magnetic stimulation cannot replace electrical neurography at the moment, even if different coils are used at different sites of stimulation.

Action Potentials↗
PubMed1994

Magnetically induced muscle contraction is caused by motor nerve stimulation and not by direct muscle activation.

When magnetically stimulating peripheral nerves, a local cocontraction of muscle under the coil is observed. We assessed whether this contraction results from: (1) magnetic stimulation of motor nerves, or (2) direct depolarization of the muscle membrane. Wrist extensor muscles of normal subjects were magnetically stimulated with the coil placed directly above the muscle. Neuromuscular transmission was then blocked by atracurium using a technique of local curarization. As a reference, the radial nerve was stimulated electrically. Magnetic and electrical stimuli were applied alternatingly every 10 s. Twitch force of wrist extension was measured isometrically over a period of about 70 min including the phase of complete neuromuscular block. Twitch amplitudes elicited by magnetic and electrical stimuli were equivalent during the whole experiment. These results suggest that muscle cocontraction following magnetic stimulation results from depolarization of terminal motor nerve branches.

Action Potentials↗
PubMed1994

Repetitive magnetic nerve stimulation: technical considerations and clinical use in the assessment of neuromuscular transmission.

We assessed to what extent repetitive magnetic stimulation can replace the electrical method. Fifteen healthy subjects and 3 patients with myasthenia gravis were investigated using stimulation of the median, ulnar, axillary and accessory nerves. Single, as well as 3/sec repetitive magnetic and electrical stimuli were applied. When comparing the results of magnetic vs. electrical stimulation, amplitudes, areas and shapes of compound muscle action potentials were not significantly different. Although single magnetic stimuli were much less uncomfortable than the electrical stimuli, differences in comfort were much smaller in the repetitive protocol, because muscular contractions under the magnetic stimulation coil caused unpleasant movements of, for example, the neck. Additional problems arose from technical limitations of the prototype magnetic stimulator used: stimulation intensity was significantly limited, resulting in an inability to elicit supramaximal responses in 11 of the 154 investigations. Overheating of the stimulator coil forced us to give the coil extra time to cool down. These problems might be solved in the future by more focused stimulus geometry and introduction of cooling devices. It is concluded that magnetic stimulation can elicit responses which are equivalent to the electrical method in repetitive nerve stimulation. At present due to some shortcomings it cannot replace electrical stimulation in routine repetitive nerve stimulation.

Adult↗
PubMed1994

Reduction of corticospinal excitability by magnetic stimulation over the cerebellum in patients with large defects of one cerebellar hemisphere.

The reduction of motor cortex excitability by magnetic stimulation over the lateral basiocciput of normal subjects has up to the present time been attributed to an activation of cerebellar structures. This hypothesis was tested in one patient with complete agenesis and two patients with extensive infarction of one cerebellar hemisphere. Unexpectedly, stimulation over the intact and absent or damaged cerebellar hemispheres reduced the susceptibility of the contralateral and, to a lesser degree, the ipsilateral motor cortex to cortical magnetic test stimuli given 9 msec after the stimulus over the cerebellum. The anatomic structure, activated by stimulation over the lateral occiput, remains unclear but activation of brain-stem structures, rather than the cerebellum, has been postulated. Increased thresholds for the excitation of the hand-associated motor cortex contralateral to the cerebellar lesion correlated with slow and clumsy finger movements ipsilateral to the cerebellar lesion, which suggests facilitatory influences of the cerebellum on the contralateral corticospinal system under normal conditions.

Adult↗
PubMed1993

The value of magnetic stimulation in the diagnosis of radiculopathies.

We studied 42 patients with cervical and lumbar radiculopathies using magnetic stimulation. Prolonged latencies following magnetic stimulation of the brain, the paravertebral spinal nerve, or both, showed a highly significant correlation with muscle weakness in clinical testing (24 of 26 patients with weakness had pathological motor evoked potentials) as well as with spontaneous activity of the target muscles in needle electromyography (24 of 25 subjects). The determination of both the central and the peripheral motor conduction time was found to be essential in patients with radiculopathies, because different patterns of latency changes correlated with different morphological results in computed tomography: in patients diagnosed as having a lateral compression of the nerve root the peripheral nerve latency was delayed; whereas, in patients with more medially localized herniations, a prolonged central motor latency was the most frequent finding. This study posits that combined magnetic stimulation of the brain and nerve root is an effective and painless technique for the noninvasive evaluation of nerve root function.

Adult↗
PubMed1993

PC-based system for an objective quantification of manual movement disability for clinical and scientific purposes.

In clinical management and research of movement disorders exact knowledge about the extent of motor impairment is essential. This paper presents a computer program which allows for an objective measurement of manual movement disability. The program was developed for standard hardware and can easily be used in a variety of clinical and research environments. The program runs on MS-DOS computers and uses a Microsoft computer mouse as the only input device. The temporal resolution is 100 Hz, the spatial resolution 400 dots per inch. The user may choose between standard test sets or he may design sets according to his individual needs from a pool of available protocols which includes tracking tasks, ballistic tasks, complex sequential tasks, and finger tapping. All tasks are implemented in a similar way in order to keep the test environment as consistent as possible for the patient. The patient must usually carry out movements which correspond to the movements of a target symbol on the computer screen. This entails the manipulation of a follower symbol, also visible on the computer screen, via the computer mouse. The program itself and the theoretical background of the protocols are described in the paper. Additionally, preliminary results from pilot experiments are presented.

Computer Simulation↗
PubMed1992

Motor responses evoked by magnetic brain stimulation in psychogenic limb weakness: diagnostic value and limitations.

The latencies and amplitudes of responses evoked by magnetic brain stimulation (magnetic evoked potentials, MEP) in the first dorsal interosseus and the anterior tibial (TA) muscles were investigated in 15 patients with psychogenic limb weakness and in 50 patients with limb weakness due to established organic central nervous system disease. Of the patients with psychogenic limb weakness, 3 presented with upper limb monopareses, 2 with lower limb monoparesis, 4 with hemipareses, 4 with parapareses and 2 with paraparesis. All patients with psychogenic weakness had MEP in arm and leg muscles with latencies within the normal range. MEP amplitudes were also normal except for 1 patient in whom the response amplitude in the TA of the plegic limb was reduced. In patients with limb weakness due to established organic disease, MEP were frequently but not invariably abnormal. In patients with plegic (i.e. completely paretic, MRC grade 0) muscles due to organic disease, MEP always were clearly abnormal. Normal MEP were sometimes elicited from paretic muscles, more commonly in association with cerebral hemisphere lesions than with spinal lesions. We conclude that psychogenic limb weakness is associated with normal MEP. However, normal MEP in mildly paretic muscles do not definitely exclude organic pathology.

Adolescent↗
PubMed1992

Motor responses evoked by magnetic brain stimulation in Huntington's disease.

In 34 patients with manifest Huntington's disease (HD), and in 21 first-degree offspring without clinical signs or symptoms, the sizes, central motor latencies (CMLs) and variation in latencies of EMG responses (MEPs) following transcranial magnetic brain stimulation were studied in muscles of the upper and lower extremities. In subgroups of patients and their offspring median and tibial nerve somatosensory evoked potentials (SEPs) and electrically elicited long-loop reflexes (LLRs) in hand muscles were also investigated. Increased MEP thresholds were observed in 10% of the HD offspring, while CML, latency variability and MEP amplitudes always lay within normal range. In contrast, SEPs were abnormal in 33%. In HD patients MEPs were found to be abnormal in up to 72% of patients when all available response parameters were taken into consideration. MEP abnormalities correlated with the duration of motor symptoms and the severity of choreic motor activity. When both MEPs and SEPs were evaluated, abnormalities could be detected in 91% of all HD patients. We suggest that abnormal MEPs might reflect an altered excitability of the cortico-spinal system as a consequence of basal ganglia dysfunction, rather than a structural damage of the investigated descending pathways. To localize the pathological mechanism responsible for altered LLRs, a "loop analysis" was performed by recording LLRs, MEPs and SEPs in the same patients. Alterations of LLRs correlated best with abnormal SEPs and might therefore be explained by reduced somatosensory input to the motor cortex.

Adolescent↗
PubMed1991

Abnormal conduction in corticospinal pathways in Wilson's disease: investigation of nine cases with magnetic brain stimulation.

Electromyographic (EMG) responses evoked by transcranial magnetic brain stimulation were studied in nine patients with Wilson's disease (WD). Six of the nine patients had prolonged central motor latencies (CMLs), reduced amplitude, or absent responses in at least one of the examined muscles. In one patient, abnormal EMG responses normalized following treatment with penicillamine. Pathophysiologically abnormal EMG responses might result from a potentially reversible impairment of corticomotoneuronal pathways and/or a reduced excitability of motoneurons due to basal ganglia dysfunction. The possible pathophysiological mechanisms are discussed.

Adult↗
PubMed1991

Is there an age-dependent continuous increase in the duration of the motor unit action potential?

The duration of the motor unit potential plays an important role in the diagnosis of neuromuscular diseases, but is also subject to physiological variations. In order to evaluate the age-related changes the mean motor unit potential duration was studied in 4 proximal and distal muscles of the upper and lower extremities in 111 healthy subjects between 20 and 80 years. Contrary to the results of previous researches no marked increase of mean duration could be found in subjects younger than 55 years. Subjects older than 55 showed a slight tendency towards increased duration of the motor unit potential. These findings are interpreted as the result of changes in fiber density and are in accordance with single fiber EMG records.

Action Potentials↗
PubMed1990

A kinematic analysis of anticipatory coarticulation in the speech of anterior aphasic subjects using electromagnetic articulography.

An investigation was made into the extent and time course of anticipatory coarticulation in the speech of two normal and two anterior aphasic, German-speaking subjects. Both labial and velar coarticulation gestures were investigated. Subjects produced sentences containing target words contrasting in postconsonantal vowel rounding (e.g., [geli:ge]/[gely:gel]) and in nasality (e.g., [ti:de]/[ti:ne]). Speech kinematics were monitored by means of electromagnetic articulography. The data revealed that for correct productions, aphasic speakers' coarticulatory patterns were more highly variable than those of control subjects. These differences, however, were found chiefly for spatial displacement characteristics, while the temporal aspects of articulator movement necessary for anticipatory coarticulation appeared largely intact. Articulator mistiming did not appear to explain a small corpus of stop/nasal substitution errors produced by one of the aphasic speakers.

Aphasia↗
PubMed1989

Changes of transcranially evoked motor responses in man by midazolam, a short acting benzodiazepine.

The present study investigated the effects of midazolam, a short acting benzodiazepine, on muscle responses elicited by magnetic brain stimulation. During continuous midazolam infusion (0.3 mg/kg/h for up to 30 min) amplitudes and durations of transcranially elicited compound muscle action potentials decreased progressively while latencies remained unchanged. The results can be accounted for by midazolam enhancement of the inhibitory action of GABAergic cortical interneurons, which decreases the excitability of pyramidal cells and reduces the number of neurons available for generation of descending pyramidal tract activity.

Action Potentials↗