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Biomedical subjects

A M Humm

Publications and source records attributed to A M Humm.

9 recordsLinked to original sources
PubMed2006

Unexplained syncope--is screening for carotid sinus hypersensitivity indicated in all patients aged >40 years?

OBJECTIVE: To determine the frequency, age distribution and clinical presentation of carotid sinus hypersensitivity (CSH) among 373 patients (age range 15-92 years) referred to two autonomic referral centres during a 10-year period. METHODS: Carotid sinus massage (CSM) was performed both supine and during 60 degree head-up tilt. Beat-to-beat blood pressure, heart rate and a three-lead electrocardiography were recorded continuously. CSH was classified as cardioinhibitory (asystole > or = 3 s), vasodepressor (systolic blood pressure fall > or = 50 mm Hg) or mixed. All patients additionally underwent autonomic screening tests for orthostatic hypotension and autonomic failure. RESULTS: CSH was observed in 13.7% of all patients. The diagnostic yield of CSM was nil in patients aged < 50 years (n = 65), 2.4% in those aged 50-59 years (n = 82), 9.1% in those aged 60-69 years (n = 77), 20.7% in those aged 70-79 years (n = 92) and reached 40.4% in those > 80 years (n = 57). Syncope was the leading clinical symptom in 62.8%. In 27.4% of patients falls without definite loss of consciousness was the main clinical symptom. Mild and mainly systolic orthostatic hypotension was recorded in 17.6%; evidence of sympathetic or parasympathetic dysfunction was found in none. CONCLUSIONS: CSH was confirmed in patients > 50 years, the incidence steeply increasing with age. The current European Society of Cardiology guidelines that recommend testing for CSH in all patients > 40 years with syncope of unknown aetiology may need reconsideration. Orthostatic hypotension was noted in some patients with CSH, but evidence of sympathetic or parasympathetic failure was not found in any of them.

Adolescent↗
PubMed2005

Quantification of central motor conduction deficits in multiple sclerosis patients before and after treatment of acute exacerbation by methylprednisolone.

OBJECTIVE: To compare the effects of intravenous methylprednisolone (IVMP) in patients with relapsing-remitting (RR-MS), secondary progressive (SP-MS), and primary progressive multiple sclerosis (PP-MS). METHODS: Clinical and neurophysiological follow up was undertaken in 24 RR-MS, eight SP-MS, and nine PP-MS patients receiving Solu-Medrol 500 mg/d over five days for exacerbations involving the motor system. Motor evoked potentials (MEPs) were used to measure central motor conduction time (CMCT) and the triple stimulation technique (TST) was applied to assess conduction deficits. The TST allows accurate quantification of the number of conducting central motor neurones, expressed by the TST amplitude ratio. RESULTS: There was a significant increase in TST amplitude ratio in RR-MS (p<0.001) and SP-MS patients (p<0.02) at day 5, paralleling an increase in muscle force. TST amplitude ratio and muscle force remained stable at two months. In PP-MS, TST amplitude ratio and muscle force did not change. CMCT did not change significantly in any of the three groups. CONCLUSIONS: In RR-MS and SP-MS, IVMP is followed by a prompt increase in conducting central motor neurones paralleled by improvement in muscle force, which most probably reflects partial resolution of central conduction block. The lack of similar clinical and neurophysiological changes in PP-MS corroborates previous clinical reports on limited IVMP efficacy in this patient group and points to pathophysiological differences underlying exacerbations in PP-MS.

Adult↗
PubMed2005

Repetitive spinal motor neuron discharges following single transcranial magnetic stimuli: a quantitative study.

OBJECTIVE: To quantify repetitive discharges of spinal motor neurons (repMNDs) in response to single transcranial magnetic stimuli (TMS). To assess their contribution to the size of motor evoked potentials (MEPs). METHODS: We combined the triple stimulation technique (TST) with an additional nerve stimulus in the periphery (= quadruple stimulation; QuadS). The QuadS eliminates the first action potential descending on each axon after TMS, and eliminates effects on response size induced by desynchronization of these discharges, thereby allowing a quantification of motor neurons (MNs) discharging twice. In some instances, a quintuple stimulation (QuintS) was used, to quantify the number of MNs discharging three times. Recordings were from the abductor digiti minimi of 14 healthy subjects, using two different stimulation intensities and three different levels of facilitatory muscle pre-contractions. RESULTS: The threshold to obtain repMNDs was high. Their maximal size differed markedly between subjects, ranging from 8 to 52% of all MNs. Stimulation intensity and facilitatory muscle contraction, but not resting motor threshold, correlated with the amount of repMNDs. QuintS never yielded discernible responses, hence all observed repMNDs were double discharges. RepMNDs contributed to the MEP areas, but did not influence MEP amplitudes. CONCLUSIONS: QuadS and QuintS allow precise quantification of repMNDs. The threshold of repMNDs is high and varies considerably between subjects. SIGNIFICANCE: repMNDs have to be considered when MEP areas are measured. Their analysis may be of interest in neurological disorders, but standardized stimulation parameters appear essential.

Action Potentials↗
PubMed2004

Assessment of central motor conduction to intrinsic hand muscles using the triple stimulation technique: normal values and repeatability.

OBJECTIVE: To establish the triple stimulation technique (TST) for recordings from the first dorsal interosseus (FDI) and the abductor pollicis brevis muscles (APB), and to analyse the test-retest repeatability of the TST measurements in APB. METHODS: The recently developed TST was slightly modified for recordings from small hand muscles to account for volume conducted activity from surrounding muscles. The TST combines transcranial magnetic stimulation (TMS) with a peripheral collision technique [Magistris et al. Brain 121 (1998) 437]. In contrast to conventional motor-evoked potentials (MEPs), it quantifies the number of conducting central motor neurons (expressed by the TST amplitude ratio, TST-AR). MEPs and TST were performed in 30 sides of 25 healthy subjects (target muscle FDI), and in 29 sides of 21 healthy subjects (target muscle APB). All APB recordings were repeated after 25+/-5.9 days. RESULTS: The TST-AR averaged 97.4+/-2.5% in FDI and 95.9+/-4.7% in APB. There was a mean difference of the TST-AR ratio of 2.9+/-3.1% between the repeated APB recordings (95% limits of agreement+/-6.3%). CONCLUSIONS: TMS allows activation of virtually all motor neurons supplying FDI and APB, when effects of volume conduction are eliminated. Its test-retest repeatability is excellent. SIGNIFICANCE: The TST is well suited for follow-up examinations of central motor conduction failures. The greater number of established target muscles widens its clinical applicability.

Adult↗
PubMed2004

Quantification of Uhthoff's phenomenon in multiple sclerosis: a magnetic stimulation study.

OBJECTIVE: To quantify temperature induced changes (=Uhthoff phenomenon) in central motor conduction and their relation to clinical motor deficits in 20 multiple sclerosis (MS) patients. METHODS: Self-assessment of vulnerability to temperature and clinical examination were performed. We used motor evoked potentials to measure central motor conduction time (CMCT) and applied the triple stimulation technique (TST) to assess conduction failure. The TST allows an accurate quantification of the proportion of conducting central motor neurons, expressed by the TST amplitude ratio (TST-AR). RESULTS: Temperature induced changes of TST-AR were significantly more marked in patients with prolonged CMCT (P=0.037). There was a significant linear correlation between changes of TST-AR and walking velocity (P=0.0002). Relationships were found between pronounced subjective vulnerability to temperature and (i) abnormal CMCT (P=0.02), (ii) temperature induced changes in TST-AR (P=0.04) and (iii) temperature induced changes in walking velocity (P=0.04). CMCT remained virtually unchanged by temperature modification. CONCLUSIONS: Uhthoff phenomena in the motor system are due to varying degrees of conduction block and associated with prolonged CMCT. In contrast to conduction block, CMCT is not importantly affected by temperature. SIGNIFICANCE: This is the first study quantifying the Uhthoff phenomenon in the pyramidal tract of MS patients. The results suggest that patients with central conduction slowing are particularly vulnerable to develop temperature-dependent central motor conduction blocks.

Adult↗
PubMed2003

Abnormal trafficking of sarcolemmal proteins in alpha-glucosidase deficiency.

The dystrophin-associated protein complex (DAP) plays an important role in the integrity and stability of the muscle membrane. Whereas much is known about the interaction between DAP members at the sarcolemmal location, intracellular DAP assembly and trafficking is still largely unknown. In alpha-glucosidase (acid maltase) deficiency (alphaGDD), accumulation of glycogen is accompanied by cytoarchitectural abnormalities impairing normal protein metabolism. In the present study, we took advantage of this fact to examine the consequences of impaired protein handling on the formation of DAP, with the aim of gaining indirect knowledge about its sarcoplasmic trafficking and a better understanding of mechanisms leading to myopathic changes found in alphaGDD. Histological examination of alphaGDD muscle confirmed a vacuolar myopathy with glycogen accumulation both in vacuoles and within the sarcoplasm. Sarcoplasmic accumulation of sarcolemmal proteins, including dystrophin and sarcoglycans, occurred around some vacuoles and within non-vacuolated fibres. Utrophin was up-regulated and found at extra-junctional sarcolemmal locations of many fibres. AlphaGDD muscle cells developed in a fashion similar to that of controls in culture. However, vacuoles were found in 2-week-old alphaGDD myotubes, and these subsequently increased in size and number. Substantial alterations in DAP handling were found, with accumulation close to the Golgi apparatus. Utrophin was not enriched in the sarcoplasm but was up-regulated along the whole sarcolemma. Our results demonstrate a close association of dystrophin and sarcoglycans during sarcoplasmic processing. Furthermore, they suggest that the myopathy found in alphaGDD is a secondary form of DAP deficiency.

Cells, Cultured↗
PubMed2003

Central motor conduction differs between acute relapsing-remitting and chronic progressive multiple sclerosis.

OBJECTIVE: To characterize central motor conduction in relation to the clinical deficits and to the disease duration in 90 patients with acute relapsing-remitting MS (RR-MS) and in 51 patients with chronic primary or secondary progressive MS (P-MS). METHODS: The triple stimulation technique (TST) was used to quantify the central motor conduction failure (expressed by the TST amplitude ratio) and conventional motor evoked potentials (MEPs) were used to measure the central motor conduction time (CMCT). RESULTS: The TST amplitude ratio was reduced in presence of a clinical motor deficit (p=0.02 for RR-MS, p<0.01 for P-MS), but did not significantly differ in RR-MS and P-MS (p>0.05) when patients with similar clinical motor deficit were compared. The CMCT was not related to the clinical motor deficit in both RR-MS and P-MS. However, the CMCT was markedly prolonged in P-MS, when patients with similar clinical motor deficit and with similar disease duration were compared (p<0.01). The differences were not attributable to differential involvement of the spinal cord, which was similar in RR-MS and P-MS. CONCLUSIONS: Our results disclose differences between the central motor conduction in RR-MS and P-MS that are not related to disease severity, spinal cord involvement or disease duration.

Acute Disease↗
PubMed2000

Enkephalin and aFGF are differentially regulated in rat spinal motoneurons after chemodenervation with botulinum toxin.

Botulinum toxin is used to induce transient graded paresis by chemodenervation in the treatment of focal hyperkinetic movement disorders. While the molecular events occurring in motoneurons after mechanical nerve lesioning leading to muscle paresis are well known, they have been investigated to a lesser extent after chemodenervation. We therefore examined the expression of enkephalin (ENK), acidic fibroblast growth factor (aFGF), neurotensin (NT), galanin (GAL), substance P (SP), vasoactive intestinal polypeptide (VIP), and neuropeptide Y (NPY) in rat spinal motoneurons after chemodenervation of the gastrocnemius. In order to precisely localize the motoneurons targeting the injection site, retrograde tracing was performed in additional rats by using Fluorogold injections. ENK expression was upregulated in the region corresponding to the Fluorogold positive motoneurons, but also on the contralateral side and in more distant parts of the spinal cord. The highest upregulation occurred 7 to 14 days after injections and decreased over a period of three months. At 8 days, aFGF was slightly downregulated in all regions studied, single motoneurons showed NT expression, while expression of GAL, SP, VIP, and NPY could be detected neither in controls nor in toxin-treated animals. These alterations in gene expression were strikingly different from those described after axotomy. Our present findings give additional demonstration of the considerable plasticity of the adult spinal cord after botulinum toxin treatment.

Age Factors↗