Impact of comorbidities and co-medication on disease onset and progression in a large German ALS patient group.

INTRODUCTION: Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disease with loss of muscle function. The pathogenesis is still unclear and the heterogeneity of ALS phenotypes is huge. We investigated a large population of ALS patients and controls concerning comorbidities and medications to detect specific risk or protective factors regarding onset and progression of ALS. METHODS: We investigated a cohort of 200 ALS patients pro- and retrospectively compared to a control group. For comparison of frequencies of comorbidities and medication intake, uni- and multivariate binary logistic regressions were performed. To analyze the influence of comorbidities and medication on the progression of ALS, we used linear regression analysis. RESULTS: ALS patients showed a relevantly higher prevalence of strokes and depression compared to controls. Moreover, ALS patients reported relevantly more often regular physical activity and their BMI was lower. The coexistence of coronary heart disease was associated with a relevantly faster disease progression. Intake of contraceptives was relevantly higher in controls compared with ALS patients. CONCLUSIONS: Our results suggest stroke, lower BMI, and regular physical activity as risk factors for ALS. Strokes could be a possible trigger of the pathogenetic pathway of ALS and the lower BMI with consecutively lower rate of hyperlipidemia supports the hypothesis of premorbid hypermetabolism in ALS patients. Coexistence of coronary heart disease possibly has a negative influence on respiratory involvement. Contraceptives could be beneficial due to a protective effect of estrogen. Information on influencing factors can help to elucidate the pathogenesis of ALS or provide approaches for possible therapeutic options.

Influence of Environment and Lifestyle on Incidence and Progress of Amyotrophic Lateral Sclerosis in A German ALS Population.

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease mainly affecting upper and lower motor neurons in the brain and spinal cord. Pathogenesis of ALS is still unclear, and a multifactorial etiology is presumed. The remarkable clinical heterogeneity between different phenotypes of ALS patients suggests that environmental and lifestyle factors could play a role in onset and progression of ALS. We analyzed a cohort of 117 ALS patients and 93 controls. ALS patients and controls were compared regarding physical activity, dietary habits, smoking, residential environment, potentially toxic environmental factors and profession before symptom onset and throughout the disease course. Data were collected by a personal interview. For statistical analysis descriptive statistics, statistical tests and analysis of variance were used. ALS patients and controls did not differ regarding smoking, diet and extent of physical training. No higher frequency of toxic influences could be detected in the ALS group. ALS patients lived in rural environment considerably more often than the control persons, but this was not associated with a higher percentage of occupation in agriculture. There was also a higher percentage of university graduates in the ALS group. Patients with bulbar onset were considerably more often born in an urban environment as compared to spinal onset. Apart from education and environment, ALS phenotypes did not differ in any investigated environmental or life-style factor. The rate of disease progression was not influenced by any of the investigated environmental and life-style factors. The present study could not identify any dietary habit, smoking, physical activity, occupational factor as well as toxic influences as risk factor or protective factor for onset or progression of ALS. Living in rural environment and higher education might be associated with higher incidence of ALS.

Motor units as tools to evaluate profile of human Renshaw inhibition.

KEY POINTS: To uncover the synaptic profile of Renshaw inhibition on motoneurons, we stimulated thick motor axons and recorded from voluntarily-activated motor units. Stimuli generated a direct motor response on the whole muscle and an inhibitory response in active motor units. We have estimated the profile of Renshaw inhibition indirectly using the response of motor unit discharge rates to the stimulus. We have put forward a method of extrapolation that may be used to determine genuine synaptic potentials as they develop on motoneurons. These optimized techniques can be used in research and in clinics to fully appreciate Renshaw cell function in various neurological disorders. ABSTRACT: Although Renshaw inhibition (RI) has been extensively studied for decades, its precise role in motor control is yet to be discovered. One of the main handicaps is a lack of reliable methods for studying RI in conscious human subjects. We stimulated the lowest electrical threshold motor axons (thickest axons) in the tibial nerve and analysed the stimulus-correlated changes in discharge of voluntarily recruited low-threshold single motor units (SMUs) from the soleus muscle. In total, 54 distinct SMUs from 12 subjects were analysed. Stimuli that generated only the direct motor response (M-only) on surface electromyography induced an inhibitory response in the low-threshold SMUs. Because the properties of RI had to be estimated indirectly using the background discharge rate of SMUs, its profile varied with the discharge rate of the SMU. The duration of RI was found to be inversely proportional to the discharge rate of SMUs. Using this important finding, we have developed a method of extrapolation for estimating RI as it develops on motoneurons in the spinal cord. The frequency methods indicated that the duration of RI was between 30 and 40 ms depending on the background firing rate of the units, and the extrapolation indicated that RI on silent motoneurons was ∼55 ms. The present study establishes a novel methodology for studying RI in human subjects and hence may serve as a tool for improving our understanding of the involvement of RI in human motor control.

Bilateral changes in afterhyperpolarization duration of spinal motoneurones in post-stroke patients.

This paper extends the observations presented in the previously published work on the afterhyperpolarization (AHP) duration changes in motoneurones (MNs) on the paretic (more affected) side of 11 post-stroke patients by the same analysis on the non-paretic (less-affected) side. The estimated AHP duration for patients' MNs supplying more-affected muscles was significantly longer than control values and the elongation decreased with patient age and disorder duration. For MNs supplying less-affected muscles, dependency of AHP duration on age was closer to the control data, but the scatter was substantially bigger. However, the AHP duration estimate of less-affected MNs tended to be longer than that of controls in the short time elapsed since the stroke, and shorter than controls in the long time. Our results thus suggest that the spinal MNs on both sides respond to the cerebral stroke rapidly with prolongation of AHP duration, which tends to normalize with time, in line with functional recovery. This suggestion is in concert with the published research on post-stroke changes in brain hemispheres. To our knowledge, these dependencies have never been investigated before. Since the number of our data was limited, the observed trends should be verified in a larger sample of patients and such a verification could take into account the suggestions for data analysis that we provide in this paper. Our data are in line with the earlier published research on MN firing characteristics post-stroke and support the conclusion that the MUs of the muscles at the non-paretic side are also affected and cannot be considered a suitable control for the MUs on the paretic side.

International Survey of ALS Experts about Critical Questions for Assessing Patients with ALS.

OBJECTIVE: To define an applicable dataset for ALS patient registries we weighted specific clinical items as scored by worldwide ALS experts. METHODS: Sixty participants were invited based on relevant clinical work, publications and personal acquaintance. They rated 160 clinical items consensually agreed by the members of our project, incorporating specialists from five European Centres. Scoring scheme was defined as: 1 - essential; 2 - important; 3 - not very important. A mixed effect model was applied to rank items and to find possible correlations with geographical region (Europe vs. outside Europe). RESULTS: We received 40 responses, 20 from Europe and 20 from outside; 42/160 data were scored as essential by >50% of the respondents, including: date of birth, gender, date of disease onset, date of diagnosis, ethnicity, region of onset, predominant upper neuron (UMN) or lower motor neuron (LMN) impairment, proximal versus distal weakness, respiratory symptoms, dysarthria, weight loss, signs of LMN/UMN involvement, emotional incontinence, cognitive changes, respiratory signs, neck weakness, body mass index, ALSFRS-R at entry, ALSFRS-R subscores at entry, timing and pattern of spreading and staging, electromyography, spirometry, MRI, CK level, riluzole intake, genetic background, history of physical exercise and previous and current main occupation. Four components were scored as non-relevant, including place of birth, blood pressure and pain at onset. There was no significant difference between regions (European vs. non-European countries). CONCLUSIONS: Our study identified a consensual set of clinical data with 42 specific items that can be used as a minimal data set for patient registers and for clinical trials.

Double discharges in human soleus muscle.

Double discharges (doublets) were recorded from human soleus (SOL), where they have never been reported before. The data analyzed in this study were collected from 12 healthy volunteers. The subjects were recruited for other studies, concerning: (1) estimation of motoneurons' (MNs) afterhyperpolarization (AHP) duration and (2) analysis of motor unit responses to nerve stimulation, and were not trained to voluntarily evoke doublets. The majority of intradoublet intervals fell into the commonly accepted range 2-20 ms. However, two SOL MNs from one presented exceptional doublets of intradoublet interval about 37 ms. This interval was virtually identical with the interval between second and third discharge in the few triplets recorded from another subject. It is hypothesized that triplets are generated by the delayed depolarization with the second narrow hump, which is the same as the hump responsible for exceptional doublets.

Analysis of motoneuron responses to composite synaptic volleys (computer simulation study).

This paper deals with the analysis of changes in motoneuron (MN) firing evoked by repetitively applied stimuli aimed toward extracting information about the underlying synaptic volleys. Spike trains were obtained from computer simulations based on a threshold-crossing model of tonically firing MN, subjected to stimulation producing postsynaptic potentials (PSPs) of various parameters. These trains were analyzed as experimental results, using the output measures that were previously shown to be most effective for this purpose: peristimulus time histogram, raster plot and peristimulus time intervalgram. The analysis started from the effects of single excitatory and inhibitory PSPs (EPSPs and IPSPs). The conclusions drawn from this analysis allowed the explanation of the results of more complex synaptic volleys, i.e., combinations of EPSPs and IPSPs, and the formulation of directions for decoding the results of human neurophysiological experiments in which the responses of tonically firing MNs to nerve stimulation are analyzed.

Motoneuron afterhyperpolarisation duration in amyotrophic lateral sclerosis.

Motor unit (MU) potentials were registered from 20 ALS patients and 13 age-matched control individuals during isometric constant force contractions of brachial biceps (BB). The registered signals were decomposed into single MU potential trains. The estimates of duration of the afterhyperpolarisation (AHP) in MNs, derived from the interspike interval variability, was compared between ALS patients (124 MNs) and control subjects (111 MNs) and no significant differences were encountered. However, the relationship between TI and age for patients appeared to be qualitatively different from that of the control group. The dependence of patients' AHPs on relative force deficit (RFD), which quantified muscle involvement, was more specific. For RFDs below 30%, the AHP estimate was significantly lower than control values and then increased thereafter with increasing RFDs. Moreover, firing rates of patients with the smallest RFDs were significantly higher while firing rates of patients with the greatest RFDs were significantly lower than control values. The AHP shortening in the early stages of muscle impairment is consistent with the decrease in firing threshold of 'fast' MNs found in spinal cord slices from neonatal SOD1 mice. The later elongation of the AHP may be caused by the higher vulnerability of 'fast' MNs to degeneration and by the influence of reinnervation. Our results are comparable to what has been observed in acute experiments in animal models, providing a bridge between animal and clinical research that may be relevant for identification of mechanism(s) underlying neurodegeneration in ALS.

Computer simulation study of the relationship between the profile of excitatory postsynaptic potential and stimulus-correlated motoneuron firing.

This paper shows the results of computer simulation of changes in motoneuron (MN) firing evoked by a repetitively applied synaptic volley that consists of a single excitatory postsynaptic potential (EPSP). Spike trains produced by the threshold-crossing MN model were analyzed as experimental results. Various output functions were applied for analysis; the most useful was a peristimulus time histogram, a special modification of a raster plot and a peristimulus time frequencygram (PSTF). It has been shown that all functions complement each other in distinguishing between the genuine results evoked by the excitatory volley and the secondary results of the EPSP-evoked synchronization. The EPSP rising edge was best reproduced by the PSTF. However, whereas the EPSP rise time could be estimated quite accurately, especially for high EPSP amplitudes at high MN firing rates, the EPSP amplitude estimate was also influenced by factors unrelated to the synaptic volley, such as the afterhyperpolarization duration of the MN or the amplitude of synaptic noise, which cannot be directly assessed in human experiments. Thus, the attempts to scale any estimate of the EPSP amplitude in millivolts appear to be useless. The decaying phase of the EPSP cannot be reproduced accurately by any of the functions. For the short EPSPs, it is extinguished by the generation of an action potential and a subsequent decrease in the MN excitability. For longer EPSPs, it is inseparable from the secondary effects of synchronization. Thus, the methods aimed at extracting information about long-lasting and complex postsynaptic potentials from stimulus-correlated MN firing, should be refined, and the theoretical considerations checked in computer simulations.

Analysis of double discharges in amyotrophic lateral sclerosis.

Double discharges of motor units (MUs) occurring during sustained voluntary muscle contractions are observed occasionally in healthy muscles and more frequently in disorders of the neuromuscular system. In healthy subjects, double discharges are generated in motoneurons (MNs) and are considered to be a sign of their increased excitability. Therefore, an analysis of their firing pattern may provide information on the state of MNs in neuromuscular diseases, particularly in amyotrophic lateral sclerosis (ALS), whose etiology remains to be disclosed. Firing patterns of MUs capable of firing double discharges were analyzed in brachial biceps of 14 patients with ALS (184 MUs) and 8 healthy control subjects (102 MUs). The incidence of MUs capable of firing double discharges was significantly higher in ALS patients (28.8%) than in controls (3.9%). The majority of doublet interval durations (range 4-8 ms) as well as firing patterns of doubling MUs did not differ between subject groups. Although our data confirm the hyperexcitability of the MN pool in ALS, analysis of firing characteristics of doubling MUs indicates that doublet generation is governed by the same mechanism as in controls, that is, by delayed depolarization. Our findings may provide insight into MN function in ALS.

Time course analysis of the effects of botulinum toxin type a on elbow spasticity based on biomechanic and electromyographic parameters.

OBJECTIVE: To quantify changes of elbow spasticity over time after botulinum toxin type A (BTX-A) injection in the upper extremity of stroke patients. DESIGN: Before-after trial in which the therapeutic effects were followed up at 2, 6, and 9 weeks after the BTX-A injection (Botox). SETTING: Hospital. PARTICIPANTS: Chronic stroke patients (N=8) with upper-limb spasticity. INTERVENTION: BTX-A was injected in upper-limb muscles, including the biceps brachii. MAIN OUTCOME MEASURES: Treatment effects were quantified as the changes in the velocity and the length dependence of hyperexcitable stretch reflexes. Manual sinusoid stretches of the elbow joint at 4 frequencies (1/3, 1/2, 1, 3/2Hz) over a movement range of 60 degrees were performed on patients by using a portable device. The Modified Ashworth Scale (MAS), biomechanic viscosity, and the reflexive electromyography threshold (RET) of the biceps brachii were used to evaluate the degree of hypertonia. RESULTS: The statistical analyses of the MAS score, biomechanic viscosity, and RET revealed a significant decrease in spasticity after the injection (all P<.05). Moreover, our quantitative parameters (biomechanic viscosity, RET) revealed small changes in spasticity after the BTX-A injection that could not be observed from clinical MAS evaluations. Five of 8 subjects showed a maximal reduction in spasticity (in terms of biomechanic viscosity value) within 6 weeks after the injection, whereas it was notable that all subjects exhibited peak RET values at either 2 or 6 weeks after the injection with variable degrees of relapse of spasticity. CONCLUSIONS: Early relapse of spasticity (within 9 weeks of the injection) can be detected from biomechanic and neurophysiologic assessments in a clinical setup. These quantitative indices provide valuable information for clinicians when making decisions to perform additional rehabilitation interventions or another BTX-A injection in the early stages of treatment.

Tetanic potentiation in motor units of rat medial gastrocnemius.

Tetanic potentiation is a phenomenon, which expresses the ability of a motor unit (MU) to increase its force output in tetanic contractions above that predicted with an assumption of algebraic summation of single twitch responses. To quantify tetanic potentiation, a coefficient TPC (tetanic potentiation coefficient) was defined as a ratio of the areas below tetanic force recording corresponding to the single stimulus contribution and that of the single twitch. Single MUs (27 Slow, 71 Fast, Fatigue Resistant, and 47 Fast, Fatigable) were isolated from the rat medial gastrocnemius muscle (MG) by ventral root splitting. TPC value was rate-dependent, with the maximum TPCmax at a certain optimal rate. The largest values of the TPCmax were obtained in the weakest and most fatigue resistant (S and weak FR) MUs. The different manifestation of staircase effect, post-tetanic and tetanic potentiation in individual MU types indicates that these phenomena may be independent of each other. We suggest that these phenomena as well as the fatigue resistance should be reexamined with protocols adjusted to the MU optimal frequency.