Terminal electrocardiographic changes in brain-dead patients.

We analyzed ECGs of 18 brain-dead patients from the time of termination of ventilation until cessation of electrocardiographic activity. Gradual slowing of the atrial mechanism was followed by AV block or a gradually slowing junctional escape rhythm. Despite progressive failure of atrial and junctional pacemakers, none had a ventricular escape rhythm. There were three terminal rhythms: (1) atrial activity only, (2) slow junctional rhythm or sinus bradycardia, or (3) ventricular tachycardia (VT). A prolonged QT interval, corrected for rate, was related to later development of VT. One hypothermic and three euthermic patients had J waves.

Clinical and electrophysiologic findings in chronic neuropathy of Lyme disease.

We evaluated 25 patients with Lyme disease and chronic peripheral neuropathy. All had immunologic evidence of exposure to Borrelia burgdorferi and no other identifiable cause of neuropathy. Neuropathic symptoms began a median of 8 months (range, 0 to 165) after erythema migrans and had been present for a median of 12 months (range, 2 to 168) prior to evaluation. Twelve patients (48%) had generally symmetric distal, nonpainful paresthesia, and another 12 (48%) had generally asymmetric radicular pain. One patient (4%) had asymptomatic neuropathy. The most common physical finding was multimodal sensory loss, which was observed in 13 patients (52%); weakness and hyporeflexia were less common. Motor or sensory nerve conduction was slightly slow in 16 patients (64%). The paresthesia group more often had abnormalities on physical examination and on nerve conduction testing than did the radicular group. In 75% to 80% of patients from both groups, however, needle examination showed denervation in paraspinal and limb muscles. Among 20 patients who underwent lumbar puncture, only one had a slight spinal fluid pleocytosis. Six months after treatment with intravenous ceftriaxone, 19 patients (76%) were clinically improved. We conclude that Lyme disease can be associated with a reversible, mild chronic axonal sensorimotor polyradiculoneuropathy or polyradiculopathy.

Cervical astrocytoma with arm rigidity: clinical and electrophysiologic features.

A 67-year-old woman developed a fixed, flexed posture of the right arm and hand due to a cervical astrocytoma. EMG showed continuous motor unit potential firing at 8 to 15 Hz with an abnormal silent period, presumably due to the loss of local spinal cord inhibitory interneuronal input.

Activity-dependent conduction in single motor units.

Vertebrate sensory and motor axons vary in their responses to submaximal stimuli as a function of time since prior activation. When two equal but submaximal stimuli are presented in pairs, the response to the second stimulus may be greater or less than the response to the first stimulus, depending on the interstimulus interval (ISI). We studied both the supernormal period (ISI between 6 and 25 msec) and the subnormal period (ISI between 25 and 100 msec) under conditions where only single motor axons were stimulated. Twenty single motor units from eight normal subjects were studied. The behavior of single units was very similar to that observed in compound motor action potentials, with the supernormal period lasting approximately 20 msec, followed by a subnormal period lasting at least 80 msec. Surprisingly, a supernormal period could be evoked by a stimulus that did not produce a response in the motor unit being studied; however, the presence of subnormality was dependent on an action potential being generated in response to the first stimulus. Based on these results, we conclude that the supernormal period does not require the opening of voltage-dependent ion channels, in contrast to the later occurring subnormal period.

Short-segment incremental studies to localize ulnar nerve entrapment at the wrist.

Precise electrophysiologic localization of ulnar neuropathy at the wrist (UNW) is often problematic. In the last year, we evaluated only two patients who presented clinically with UNW. Routine electrophysiologic techniques were nondiagnostic for UNW. In contrast, short-segment incremental studies (SSIS) across the wrist demonstrated conduction block and segmental slowing of nerve conduction across the wrist in both patients. We conclude that SSIS is a valuable tool for diagnosis, precise localization, and prognosis of UNW.

Memory impairment and depression in patients with Lyme encephalopathy: comparison with fibromyalgia and nonpsychotically depressed patients.

Lyme encephalopathy, primarily manifested by disturbances in memory, mood, and sleep, is a common late neurologic manifestation of Lyme disease. We compared 20 patients with Lyme encephalopathy with 11 fibromyalgia patients and 11 nonpsychotically depressed patients using the California Verbal Learning Test, Wechsler Memory Scale, Rey-Osterrieth Complex Figure Test, Minnesota Multiphasic Personality Inventory (MMPI), and Beck Depression Inventory. Compared with patients with fibromyalgia or depression, the Lyme encephalopathy group showed mild, but statistically significant, memory deficits on two of the three memory tests. In contrast, the patients with fibromyalgia scored significantly higher than both other groups on the MMPI scale most sensitive to somatic concerns (scale 1), while the depressed patients scored higher than the Lyme patients on the scales most sensitive to depression (scale 2) and anxiety (scale 7). Physical complaints and depression were not major factors in memory performance among Lyme patients. These data support the hypothesis that Lyme encephalopathy is caused by CNS dysfunction and cannot be explained as a psychological response to chronic illness.

Cervical root stimulation in the diagnosis of radiculopathy.

Cervical root stimulation (CRS) was compared with conventional EMG, nerve conduction, and late response studies in 34 patients with possible cervical radiculopathy. Cervical roots were stimulated by monopolar needles inserted into paraspinal muscles, recording compound muscle action potentials in biceps, triceps, and abductor digiti minimi muscles. In 18 patients with clinical evidence of radiculopathy, EMG was abnormal in 11 (61%), but CRS was abnormal in all 18. Of 16 patients with symptoms but no signs of radiculopathy, EMG was abnormal in 5 (31%) and CRS was abnormal in 9 (56%).

Root stimulation studies in the evaluation of patients with motor neuron disease.

Nerve root stimulation may be employed in patients with motor neuron disease (MND) to rule out motor neuropathy with conduction block. The diagnostic utility of these studies is unknown, in part because the range of amplitude changes across nerve root segments in patients with active neuronal degeneration has not been well studied. We reviewed root stimulation studies in 32 patients (59 nerves) with MND and found segmental amplitude reduction from 0 to 45%, a range similar to values reported for normal subjects; there was no suggestion of conduction block based on our usual criteria.

A case of Hodgkin's lymphoma producing neuromyotonia.

The syndrome of neuromyotonia produces muscle stiffness, cramps, and frequently, excessive sweating. Most cases are idiopathic, but some are associated with neoplasms, especially immune cell cancers. Voltage-gated potassium channels may be the target of an autoantibody attack in idiopathic generalized neuromyotonia (Isaacs' syndrome). The cases associated with neoplasms may also have an autoimmune etiology. We report the first case of neuromyotonia as the presenting feature of Hodgkin's lymphoma and propose a paraneoplastic mechanism that would link the purported autoimmune etiology in Isaacs' syndrome with the cancer-associated cases.

Lumbrical sparing in carpal tunnel syndrome: anatomic, physiologic, and diagnostic implications.

Motor axons supplying lumbrical muscles are less severely affected than axons supplying thenar muscles in the carpal tunnel syndrome; sometimes lumbrical motor fibers are less affected than digit 2 sensory fibers. This pattern is consistent with compression of both the anterior and posterior aspects of the median nerve in the carpal tunnel because nerve fibers responsible for thenar, lumbrical, and digit 2 functions lie in an anterior-posterior gradient within the distal median nerve. Recognition of lumbrical sparing supports the electrodiagnosis of carpal tunnel syndrome when the distal latency to thenar muscles or the palm-to-wrist mixed median nerve conduction velocity is normal.

Peripheral neuropathy, high serum IgM, and paraproteinemia in mother and son.

A mother and son had peripheral neuropathy, abnormal elevation of serum IgM, and paraproteinemia. These patients may have a familial disorder of immune regulation with antibody-mediated neuropathy or a familial neuropathy with a secondary immune response.

Nonvasculitic, steroid-responsive mononeuritis multiplex.

We report two patients with mononeuritis multiplex, both of whom had focal inflammation of the perineurium and endoneurium on sural nerve biopsy without necrosis of blood vessel walls, histologic evidence of lymphoid malignancy, or mycobacterial infection. The predominant early sensory symptoms were asymmetric pain and paresthesias; subsequently, muscle weakness developed. Electrophysiologic studies showed an asymmetric sensorimotor axon loss radiculoneuropathy with denervation of limb and paraspinal muscles. Spinal fluid protein was elevated in one patient. There was no cause or underlying systemic disease. Marked improvement occurred with steroid therapy.

Reversible cerebral hypoperfusion in Lyme encephalopathy.

Lyme encephalopathy (LE) presents with subtle neuropsychiatric symptoms months to years after onset of infection with Borrelia burgdorferi. Brain magnetic resonance images are usually normal. We asked whether quantitative single photon emission computed tomography (SPECT) is a useful method to diagnose LE, to measure the response to antibiotic therapy, and to determine its neuroanatomic basis. In 13 patients with objective evidence of LE, SPECT demonstrated reduced cerebral perfusion (mean perfusion defect index [PDI] = 255), particularly in frontal subcortical and cortical regions. Six months after treatment with 1 month of intravenous ceftriaxone, perfusion significantly improved in all 13 patients (mean PDI = 188). In nine patients with neuropsychiatric symptoms following Lyme disease, but without objective abnormalities (e.g., possible LE), perfusion was similar to that of the treated LE group (mean PDI = 198); six possible LE patients (67%) had already received ceftriaxone prior to our evaluation. Perfusion was significantly lower in patients with LE and possible LE than in 26 normal subjects (mean PDI = 136), but 4 normal subjects (15%) had low perfusion in the LE range. We conclude that LE patients have hypoperfusion of frontal subcortical and cortical structures that is partially reversed after ceftriaxone therapy. However, SPECT cannot be used alone to diagnose LE or determine the presence of active CNS infection.

Proximally evoked soleus H reflexes in the evaluation of axonal neuropathy.

It is sometimes difficult to differentiate physiologically distal axonopathy from proximal root or nerve disease. Standard soleus H reflexes evoked by distal tibial nerve stimulation at the popliteal fossa are often absent in both syndromes. In this study we distinguish the two by the presence or absence of soleus H reflexes evoked by proximal sciatic nerve stimulation at the gluteal fold. In 12 normal subjects maximum H reflex amplitudes evoked by distal tibial and proximal sciatic stimulation were essentially equal. In 12 patients with suspected distal polyneuropathy, proximal but not distal stimulation evoked H reflexes. By contrast, in 10 patients with lumbosacral root or proximal nerve disease, both proximal and distal stimulation failed to elicit H reflexes. In 2 patients with lower motor neuronopathy, low but comparable amplitude H reflexes were evoked at both sites. We conclude that the presence of a proximally evoked soleus H reflex may provide specific evidence of distal axonopathy when standard soleus H reflexes are absent.

Radial neuropathy.

The radial nerve is the largest branch of the brachial plexus, and is commonly involved in upper extremity mononeuropathies. The radial nerve is primarily responsible for motor innervation of the upper extremity extensors, as well as receiving cutaneous innervation from most of the posterior arm, forearm, and hand. There are a variety of sites at which the radial nerve is susceptible to trauma and entrapment. Localizing radial nerve lesions is dependent on clinical knowledge of radial nerve anatomy, and sensory and motor examination.

The mixed nerve silent period in normal subjects and patients with amyotrophic lateral sclerosis.

The mixed nerve silent period (MNSP) is the period of motor inhibition observed when the mixed nerve innervating a voluntary activated muscle is electrically stimulated. The etiology of the MNSP is multifactorial, with the early and middle phases likely to be related to the effects of antidromic motor nerve activity on peripheral nerve and spinal interneurons. The terminal portion of the MNSP is mediated primarily by small diameter myelinated afferent fibers. The duration and latency of the MNSP vary as a function of both strength of stimulation and level of voluntary activation. In this study, we varied both stimulus strength and exertion, and compared MNSPs in 6 normal subjects with those obtained from 8 patients with amyotrophic lateral sclerosis (ALS). Differences between patients and control subjects included a longer duration of the MNSP in ALS patients, as well as less complete inhibition in the middle phases of the period. The longer duration of the MNSP may reflect an abnormality of sensory motor processing in ALS patients. The physiology underlying the incomplete inhibition is unclear, but may reflect abnormalities in Renshaw cell function.

Evidence in support of a feedback-sensitive central timekeeper for an over-learned repetitive motor behavior (pencil shading).

PURPOSE: To demonstrate the presence of a CNS timekeeper for an over-learned repetitive voluntary movement (pencil shading), and to learn if the timekeeper is influenced by changes in sensory feedback. METHODS: Self-paced pencil shading; fast, maximally-fast, and slow hand waving, as well as enhanced physiologic tremor (EPT) were recorded on 3 separate occasions with a surface-mounted accelerometer placed on the hand in 9 normal volunteers. Variation in inter-trial peak frequency was calculated. Shading and EPT were also recorded with and without visual masking in 9 normals and in 2 deafferented patients. Variation in intra-trial beat-to-beat intervals, a measure of movement regularity, was calculated. RESULTS: Shading and maximally-fast waving displayed preferred frequencies with no more variability in peak frequency between trials than did EPT, while slow and fast waving had significant inter-trial variability. Variation in beat-to-beat intervals for the shading task was less in controls than for EPT, and less in controls than for the patients in both the masked and unmasked conditions. In addition, in the masked condition, pencil shading by the patients was performed with much higher amplitude and lower frequency than by the controls. CONCLUSIONS: These data support the hypothesis that certain repetitive voluntary movements, such as pencil shading, are paced by central timekeepers that are influenced by changes in sensory feedback.

Effect of agonist load on fastest muscle contractions in human elbow flexors.

The purpose of this study was to investigate whether the central nervous system (CNS) motor program subserving most-rapid voluntary force pulse generation is modified according to the level of agonist muscle load maintained prior to the pulse. Five normal subjects produced most-rapid force pulses to a target of 20% maximum voluntary force (MVF) above different levels of steady tonic contraction. Time to reach peak force, the first agonist burst duration and area were relatively constant for loads up to approximately 40% of MVF and then increased substantially with larger loads. These results indicate that the CNS adjusts agonist burst amplitude and duration in order to accomplish the same rapid motor task depending on the load. It is argued that these adjustments are necessary to compensate for physiological limitations of motor unit behavior and non-linearity between EMG activity and phasic force output.

[Chronic neuroborreliosis in Lyme disease]. / Khronicheskii neiroborrelioz pri laimskoi bolezni.

Acute and chronic syndromes of Lyme neuroborreliosis are recognized. Acute syndromes are clinically pronounced and comprise meningitis, neuritis of the cranial nerve, radiculoneuritis. Chronic syndromes are less evident. These are moderate encephalopathy and radiculoneuropathy. The diagnosis of the chronic syndrome is based on the presence of early classic signs of BL. CSF must be tested for routine procedure and in pair with serum in the test for selective accumulation of antibodies to Bb in the CSF. Neurophysiological studies help detect memory defects. Electrophysiological tests verify radiculoneuropathy. NMR investigation of the brain and SPECT-scanning may demonstrate damage to the white brain matter. We have much experience with i.v. administration of ceftriaxone (2 g/day for 4 weeks) which relieved neurological syndromes several months later.

Mexiletine is an effective antimyotonia treatment in myotonic dystrophy type 1.

OBJECTIVE: To determine if mexiletine is safe and effective in reducing myotonia in myotonic dystrophy type 1 (DM1). BACKGROUND: Myotonia is an early, prominent symptom in DM1 and contributes to decreased dexterity, gait instability, difficulty with speech/swallowing, and muscle pain. A few preliminary trials have suggested that the antiarrhythmic drug mexiletine is useful, symptomatic treatment for nondystrophic myotonic disorders and DM1. METHODS: We performed 2 randomized, double-blind, placebo-controlled crossover trials, each involving 20 ambulatory DM1 participants with grip or percussion myotonia on examination. The initial trial compared 150 mg of mexiletine 3 times daily to placebo, and the second trial compared 200 mg of mexiletine 3 times daily to placebo. Treatment periods were 7 weeks in duration separated by a 4- to 8-week washout period. The primary measure of myotonia was time for isometric grip force to relax from 90% to 5% of peak force after a 3-second maximum grip contraction. EKG measurements and adverse events were monitored in both trials. RESULTS: There was a significant reduction in grip relaxation time with both 150 and 200 mg dosages of mexiletine. Treatment with mexiletine at either dosage was not associated with any serious adverse events, or with prolongation of the PR or QTc intervals or of QRS duration. Mild adverse events were observed with both placebo and mexiletine treatment. CONCLUSIONS: Mexiletine at dosages of 150 and 200 mg 3 times daily is effective, safe, and well-tolerated over 7 weeks as an antimyotonia treatment in DM1. CLASSIFICATION OF EVIDENCE: This study provides Class I evidence that mexiletine at dosages of 150 and 200 mg 3 times daily over 7 weeks is well-tolerated and effective in reducing handgrip relaxation time in DM1.