The stimulus-response curve and motor unit variability in normal subjects and subjects with amyotrophic lateral sclerosis.

The behavior and stability of motor units (MUs) in response to electrical stimulation of different intensities can be assessed with the stimulus-response curve, which is a graphical representation of the size of the compound muscle action potential (CMAP) in relation to stimulus intensity. To examine MU characteristics across the whole stimulus range, the variability of CMAP responses to electrical stimulation, and the differences that occur between normal and disease states, the curve was studied in 11 normal subjects and 16 subjects with amyotrophic lateral sclerosis (ALS). In normal subjects, the curve showed a gradual increase in CMAP size with increasing stimulus intensity, although one or two discrete steps were sometimes observed in the upper half of the curve, indicating the activation of large MUs at higher intensities. In ALS subjects, large discrete steps, due to loss of MUs and collateral sprouting, were frequently present. Variability of the CMAP responses was greater than baseline variability, indicating variability of MU responses, and at certain levels this variability was up to 100 microVms. The stimulus-response curve shows differences between normal and ALS subjects and provides information on MU activation and variability throughout the curve.

Relationship between symptoms and disordered continence mechanisms in women with idiopathic faecal incontinence.

BACKGROUND AND AIMS: Anal sphincter weakness and rectal sensory disturbances contribute to faecal incontinence (FI). Our aims were to investigate the relationship between symptoms, risk factors, and disordered anorectal and pelvic floor functions in FI. METHODS: In 52 women with "idiopathic" FI and 21 age matched asymptomatic women, we assessed symptoms by standardised questionnaire, anal pressures by manometry, anal sphincter appearance by endoanal ultrasound and magnetic resonance imaging (MRI), pelvic floor motion by dynamic MRI, and rectal compliance and sensation by a barostat. RESULTS: The prevalence of anal sphincter injury (by imaging), reduced anal resting pressure (35% of FI), and reduced squeeze pressures (73% of FI) was higher in FI compared with controls. Puborectalis atrophy (by MRI) was associated (p<0.05) with FI and with impaired anorectal motion during pelvic floor contraction. Volume and pressure thresholds for the desire to defecate were lower, indicating rectal hypersensitivity, in FI. The rectal volume at maximum tolerated pressure (that is, rectal capacity) was reduced in 25% of FI; this volume was associated with the symptom of urge FI (p<0.01) and rectal hypersensitivity (p = 0.02). A combination of predictors (age, body mass index, symptoms, obstetric history, and anal sphincter appearance) explained a substantial proportion of the interindividual variation in anal squeeze pressure (45%) and rectal capacity (35%). CONCLUSIONS: Idiopathic FI in women is a multifactorial disorder resulting from one or more of the following: a disordered pelvic barrier (anal sphincters and puborectalis), or rectal capacity or sensation.

Chronic immune sensory polyradiculopathy: a possibly treatable sensory ataxia.

BACKGROUND: Chronic inflammatory neuropathies can present with a sensory ataxia due to involvement of dorsal root ganglia (DRG) or sensory nerves. Selective inflammatory involvement of sensory nerve roots proximal to the DRG has been postulated. METHODS: The authors identified 15 patients with a sensory syndrome and normal nerve conduction studies. Sensory nerve root involvement was suggested by either somatosensory evoked potential (SSEP) or imaging abnormalities. CNS disease was excluded. RESULTS: All patients had gait ataxia, large fiber sensory loss, and paresthesias, and nine had frequent falls. The disease course was chronic and progressive (median duration 5 years, range 3 months to 18 years). Sural sensory nerve action potential amplitudes were preserved and SSEP abnormalities were consistent with sensory nerve root involvement. Five patients had enlargement of lumbar nerve roots on MRI with enhancement in three. The CSF protein was elevated in 13 of 14 patients tested. Three patients had lumbar sensory rootlet biopsies that showed thickened rootlets, decreased density of large myelinated fibers, segmental demyelination, onion-bulb formation, and endoneurial inflammation. Six patients who required aids to walk were treated with immune modulating therapy and all had marked improvement with four returning to normal ambulation. CONCLUSION: Based on the described clinical features, normal nerve conduction studies, characteristic somatosensory evoked potential (SSEP) abnormality, enlarged nerve roots, elevated CSF protein, and inflammatory hypertrophic changes of sensory nerve rootlet tissue, we suggest the term chronic immune sensory polyradiculopathy (CISP) for this syndrome. This condition preferentially affects large myelinated fibers of the posterior roots, may respond favorably to treatment, and may be a restricted form of chronic inflammatory demyelinating polyradiculoneuropathy.

Determinants of pain in needle electromyography.

OBJECTIVES: Although previous literature has attempted to characterize patients' pain during electromyography (EMG) based on the size and type of needle used, none have assessed the relationship between the needle insertion technique and pain. METHODS: The effects of needle type and needle movement within muscle on the immediate and residual pain during needle EMG were measured in a double-blind study of 48 patients with diverse clinical problems but no sensory loss. RESULTS: The results demonstrate that when using a standard insertion technique characterized by large needle movement, the monopolar needles were less painful than concentric needle electrodes. However, when using small needle movements (1 mm or less), pain associated with concentric needles was significantly reduced with no difference between the needle types. Examiner experience, gender, previous EMG, reported pain tolerance, pain on nerve conduction studies and other factors did not predict the amount of pain. The type of needle and type of needle movement did not effect the sensitivity of identifying abnormalities. CONCLUSIONS: These findings would support the hypothesis that although a monopolar needle electrode is less painful when using a standard technique, the needle-handling technique, specifically small needle movements, plays a large role in determining pain when using concentric needle electrodes.

Linkage of familial amyotrophic lateral sclerosis with frontotemporal dementia to chromosome 9q21-q22.

CONTEXT: Occasionally, 2 or more major neurodegenerative diseases arise simultaneously. An understanding of the genetic bases of combined disorders, such as amyotrophic lateral sclerosis (ALS) with frontotemporal dementia (FTD), will likely provide insight into mechanisms of these and related neurodegenerative diseases. OBJECTIVE: To identify loci that contain genes whose defects cause ALS. DESIGN: A genome-wide linkage analysis of 2 data sets from an ongoing study begun in the mid-1980s at 4 university research centers. SUBJECTS: An initial subset of 16 families (549 people) potentially informative for genetic analysis, in which 2 or more individuals were diagnosed as having ALS, identified from a Boston data set of 400 families and 4 families potentially informative (244 people) subsequently identified from a Chicago data set of more than 300 families to test a hypothesis based on findings from the Boston families. MAIN OUTCOME MEASURES: Linkage calculations assuming autosomal dominant inheritance with age-dependent penetrance (a parametric logarithm-of-odds [lod] score of 1.0 or greater required for further study of a potential locus); crossover analysis involving the ALS-FTD locus. RESULTS: In a set of families in which persons develop both ALS and FTD or either ALS or FTD alone, a genetic locus that is linked to ALS with FTD located between markers D9S301 and D9S167 was identified on human chromosome 9q21-q22. Families with ALS alone did not show linkage to this locus. Crossover analysis indicates this region covers approximately 17 cM. CONCLUSION: These data suggest that a defective gene located in the chromosome 9q21-q22 region may be linked to ALS with FTD. JAMA. 2000;284:1664-1669.

Electrodiagnostic studies in amyotrophic lateral sclerosis and other motor neuron disorders.

The clinical electrodiagnostic medicine (EDX) consultant asked to assess patients with suspected amyotrophic lateral sclerosis (ALS) has a number of responsibilities. Among the most important is to provide a clinical assessment in conjunction with the EDX study. The seriousness of the diagnoses and their enormous personal and economic impact require a high-quality EDX study based on a thorough knowledge of and experience with motor neuron diseases (MNDs) and related disorders. Clinical evaluation will help determine which of the EDX tools available to the EDX consultant should be applied in individual patients. Although electromyography (EMG) and nerve conduction study are the most valuable, each of the following may be helpful in the assessment of selected patients based on their clinical findings: repetitive nerve stimulation, motor unit number estimate, single-fiber EMG, somatosensory evoked potential, autonomic function test, and polysomnography. The pertinent literature on these is reviewed in this monograph. The selection and application of these EDX tools depend on a thorough knowledge of the MNDs and related disorders.

Subacute sensory neuropathy associated with Epstein-Barr virus.

A 35-year-old man experienced severe sensory loss, pseudoathetosis, and areflexia during recovery from a severe viral illness. Sensory nerve action potentials were absent, motor conduction velocities were mildly slowed, and blink reflexes were normal. Magnetic resonance imaging (MRI) revealed abnormal signal within the central and dorsal aspects of the thoracic cord. Acute and convalescent Epstein-Barr virus (EBV) titers suggested EBV as the etiology. Subacute sensory neuropathy, with peripheral and central nervous system involvement, is a rare complication of EBV infection.

Motor and sensory conduction blocks preceding severe axonal loss in guillain-barré syndrome.

We describe a patient with Guillain-Barré syndrome in whom electrophysiological studies performed 9 days after onset demonstrated multiple focal motor and sensory conduction blocks. Repeat studies 8 weeks later demonstrated complete absence of motor and sensory responses in the arm or leg. These findings suggest that early focal conduction block in sensory nerves might account for sensory symptoms and that there is a spectrum of immune-mediated injury that can proceed from myelin damage to axonal destruction.

Facial nerve electromyography and other cranial nerve monitoring.

Cranial nerves can be damaged during a variety of surgical procedures. The function of the cranial nerves can be monitored during surgery with electromyography (EMG), compound nerve and muscle action potentials (MAP), and auditory evoked potentials (AEP). We report important technical considerations that allow reliable recordings of these modalities during surgery, the criteria for determining a significant change in these electrophysiologic measures of function, the application of these techniques to specific surgical procedures, and the data that support the utility of cranial nerve monitoring.

Lack of progression of neurologic deficit in survivors of paralytic polio: a 5-year prospective population-based study.

We completed a prospective, population-based cohort study of polio survivors in Olmsted County, Minnesota, between 1986 and 1993. We identified 50 individuals who had had paralytic polio between 1935 and 1960, as representative of all 300 cases of paralytic polio in the county. We completed detailed quantitative clinical and electrophysiologic studies at entry and after 5 years. These studies demonstrated stable neuromuscular function within the cohort, although 60% of the individuals were symptomatic. In two-thirds of the symptomatic patients, the causes of their symptoms were unrelated to earlier polio. For the 20% of patients who had unexplained muscle pain, perception of weakness, and fatigue, a mechanical disorder most likely underlies their symptoms.

Estimating the number of motor units in a muscle.

A loss of motor units is the primary defect in many neurogenic disorders. The number of motor units remaining in a muscle or group of muscles can be estimated by a number of methods on either needle electromyography or as part of nerve-conduction studies. Comparison of the methods of motor unit number estimates (MUNE) and their underlying assumptions shows that each method can provide reliable and useful clinical information. Each method relies on obtaining an estimate of the average size of single motor units, and compares that size with the size of a maximal compound muscle action potential in which all motor units are activated. The potential errors of all the methods are similar and relate primarily to adequacy of sampling of the size of single motor units. The method of statistical estimates of MUNE does not attempt to isolate and measure individual motor unit potential sizes. Rather it estimates the size of single motor units from the variation in size of a muscle action potential when individual motor units in a group of motor units fire randomly.