Application of a computational model of vagus nerve stimulation.

OBJECTIVES: The most widely used and studied neurostimulation procedure for medically refractory epilepsy is vagus nerve stimulation (VNS) Therapy. The goal of this study was to develop a computational model for improved understanding of the anatomy and neurophysiology of the vagus nerve as it pertains to the principles of electrical stimulation, aiming to provide clinicians with a systematic and rational understanding of VNS Therapy. MATERIALS AND METHODS: Computational modeling allows the study of electrical stimulation of peripheral nerves. We used finite element electric field models of the vagus nerve with VNS Therapy electrodes to calculate the voltage field for several output currents and studied the effects of two programmable parameters (output current and pulse width) on optimal fiber activation. RESULTS: The mathematical models correlated well with strength-duration curves constructed from actual patient data. In addition, digital constructs of chronic versus acute implant models demonstrated that at a given pulse width and current combination, presence of a 110-µm fibrotic tissue can decrease fiber activation by 50%. Based on our findings, a range of output current settings between 0.75 and 1.75 mA with pulse width settings of 250 or 500 µs may result in optimal stimulation. CONCLUSIONS: The modeling illustrates how to achieve full or nearly full activation of the myelinated fibers of the vagus nerve through output current and pulse width settings. This knowledge will enable clinicians to apply these principles for optimal vagus nerve activation and proceed to adjust duty cycle and frequency to achieve effectiveness.

Neurologic evaluation of the upper extremity.

Symptoms and disease processes can overlap, and neurologic symptoms of the hand or arm are not necessarily due to local pathology. To combat these difficulties, the authors present a basic review of neuroanatomy, the neurologic examination, the principles of electromyography, and the process of formulation.

Electrodiagnostic reports of median neuropathy at the wrist.

The diagnosis of carpal tunnel syndrome (CTS) is confirmed by electrodiagnostic testing. Practice parameters for electrodiagnostic testing of CTS have been defined in a summary statement published by the American Academy of Neurology, the American Association of Electrodiagnostic Medicine, and the American Academy of Physical Medicine and Rehabilitation. All members of the Industrial Injuries and Prevention Committee of the American Society for Surgery of the Hand provided electrodiagnostic reports from their office practices indicating an electrodiagnosis of CTS or median neuropathy at the wrist. One hundred consecutive reports were analyzed to determine how often these electrodiagnostic studies adhered to the standards and guidelines of the summary statement. Variability in the thoroughness of the studies, hence in the quality of information in the reports, was noted. The clinical implications of this survey are that some patients were diagnosed and treated for CTS who did not have median neuropathy at the wrist.

A case-control study of obesity as a risk factor for carpal tunnel syndrome in a population of 600 patients presenting for independent medical examination.

Pain, numbness, and tingling through the median nerve distribution, known as carpal tunnel syndrome (CTS), has been associated with many personal risk factors. Previous studies have implicated obesity as a risk factor for median neuropathy at the carpal tunnel. A case-control design was undertaken to explore the association between obesity and CTS. Six hundred patients presented with symptoms of upper-extremity disorders for independent medical examination related to a disability or compensation claim. The 300 patients with electrodiagnostic evidence of CTS were compared with 300 control subjects from the same initial population. All patients were categorized according to their body mass index. The analysis was stratified for the possible confounding factors of cervical spine abnormalities, Martin-Gruber interconnections, age, and sex. A statistically significant association was found between obesity and median neuropathy. The implications of such a relationship are discussed in light of the contemporary debate over the etiology of cumulative trauma disorders.

Neurological evaluation of occupational hand pain.

The evaluation of the patient with pain, weakness, or numbness of the hand or upper extremity begins with knowledge of neuroanatomy and of the proper examination techniques. Neurological diseases of the peripheral nerves or central nervous system often present with vague complaints or minimal findings on clinical examination that may be diagnosed only with a combination of radiologic and neurodiagnostic studies. However, tests alone cannot determine the best treatment as each case must be individualized. An understanding of the utility and limitations of the electromyogram and nerve conduction studies is important when treating these patients.

Occupational neurology and the hand. Differential diagnosis.

Occupationally related dysfunction of the peripheral nervous system is a common problem. The signs and symptoms of neurologic problems of the upper extremity and neck that can alter hand function and sensation are described in detail.

Cinromide in the treatment of absence seizures.

Cinromide (BW-122U) was evaluated in an open pilot study of absence seizures in three naive (previously untreated for absence seizures) patients (one male and two females, 7 to 8 years of age). In these naive patients, cinromide was found to be well tolerated but ineffective in reducing generalized spike-and-wave discharges on the telemetered EEG during the 1-week duration of the study.

Late-onset Mcardle's disease with unusual electromyographic findings.

Symptoms of McArdle's disease (muscle phosphorylase deficiency) commonly begin in childhood or adolescence. Late onset of the disease is rare. We describe a 76-year-old man whose symptoms began at age 74 years with sudden onset of proximal muscle weakness and fatigability. Electromyography disclosed substantial spontaneous activity and myopathic features as seen in inflammatory muscle disease. The diagnosis of McArdle's disease was made by histochemical studies of muscle, an abnormal ischemic lactate test, and absence of myophosphorylase activity.