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Biomedical subjects

N R Holland

Publications and source records attributed to N R Holland.

13 recordsLinked to original sources
PubMed1998

Intraoperative electromyography during thoracolumbar spinal surgery.

Intraoperative electromyography can provide useful information regarding lumbosacral nerve root function during thoracolumbar spinal surgery. Free-running electromyography provides continuous feedback regarding the location and potential for surgical injury to the lumbosacral nerve roots within the operative field. Stimulus-evoked electromyography can confirm that transpedicular instrumentation has been positioned correctly within the bony cortex. However, electromyography has a number of potential limitations, which are discussed in this article along with improved methods to increase the overall efficacy of intraoperative electromyography, including: 1) Electromyography is sensitive to blunt lumbosacral nerve root irritation or injury, but may provide misleading results with "clean" nerve root transection. 2) Electromyography must be recorded from muscles belonging to myotomes appropriate for the nerve roots considered at risk from surgery. 3) Electromyography can be effective only with careful monitoring and titration of pharmacologic neuromuscular junction blockade. 4) When transpedicular instrumentation is stimulated, an exposed nerve root should be stimulated directly as a positive control whenever possible. 5) Pedicle holes and screws should be stimulated with single shocks at low-stimulus intensities when pharmacologic neuromuscular blockade is excessive. 6) Chronically compressed nerve roots that have undergone axonotmesis (wallerian degeneration) have higher thresholds for activation from electrical and mechanical stimulation. 7) Hence, whenever axonotmetic nerve root injury is suspected, the stimulus thresholds for transpedicular holes and screws must be specifically compared with those required for the direct activation of the adjacent nerve root (and not published guideline threshold values).

Electromyography↗
PubMed1998

Higher electrical stimulus intensities are required to activate chronically compressed nerve roots. Implications for intraoperative electromyographic pedicle screw testing.

STUDY DESIGN: A comparison of the electrical thresholds required to evoke myogenic responses from direct stimulation of normal and chronically compressed nerve roots. OBJECTIVE: To determine whether intraoperative electromyographic testing to confirm the integrity of instrumented pedicles should be performed at higher stimulus intensities in cases where there is preoperative lumbosacral radiculopathy. SUMMARY OF BACKGROUND DATA: Postoperative neurologic deficits may occur as a result of pedicle screw misplacement during spinal instrumentation. The failure to evoke myogenic responses from stimulation of pedicle holes and screws at intensities of 6-8 mA is commonly used to exclude bony pedicular wall perforation. METHODS: Direct nerve root stimulation was used to compare the stimulus thresholds of normal and compressed nerve roots in six patients with limb weakness from chronic lumbosacral radiculopathy. RESULTS: The stimulus thresholds of chronically compressed nerve roots significantly exceeded those of normal nerve roots, indicating partial axonal loss (axonotmesis). In most cases, the direct stimulus thresholds of compressed nerve roots exceeded 10 mA. CONCLUSIONS: When instrumentation is placed at spinal levels where there is preexisting chronic lumbosacral radiculopathy, holes and screws may need to be stimulated at higher intensities to exclude pedicular perforation and prevent further iatrogenic nerve root injury.

Action Potentials↗
PubMed1998

Small-fiber sensory neuropathies: clinical course and neuropathology of idiopathic cases.

We describe the clinical features, natural history, and neuropathology of 32 patients presenting with "burning feet," for whom no specific cause was identified. All had neuropathic pain in the feet and morphological abnormalities of cutaneous innervation in skin obtained using punch biopsy. Most (29) had an abnormal sensory examination. All had normal strength, proprioception, tendon reflexes, and nerve conductions. Two clinical patterns were apparent, based on natural history and spatial distribution of cutaneous denervation. Most (28) patients presented with neuropathic pain initially restricted to the feet and toes but extending more proximally to involve the legs and hands with time. Intraepidermal nerve fiber (IENF) density was most severely reduced distally, with more normal IENF densities in skin from proximal sites. In contrast, a minority (4) presented with the abrupt onset of generalized cutaneous burning pain and hyperesthesia. In these patients, IENF densities were reduced in skin from both proximal and distal sites. Absolute IENF densities in calf skin were reduced below the lower limit of normal (5th percentile) in 26 (81%). Of the 6 who underwent sural nerve biopsy, 4 had selective loss of small myelinated and/or unmyelinated axons and 2 had normal histology and fiber densities despite reduced IENF densities in skin biopsy specimens. Punch skin biopsy from proximal and distal sites is a useful means of assessing these distinctive patients and may provide further insight into pathophysiology.

Adult↗
PubMed1998

Subcortical strokes from intracranial aneurysm surgery: implications for intraoperative neuromonitoring.

Forty-five patients underwent surgery for anterior circulation aneurysms using intraoperative neurophysiologic monitoring at the Johns Hopkins Hospital during 1996. There were seven intraoperative strokes. Two were cortical strokes associated with irreversible somatosensory evoked potential (SEP) changes during temporary arterial occlusion. The remaining five were subcortical strokes, one of which was associated with transient SEP changes during temporary arterial occlusion, but the other four occurred despite normal SEPs throughout surgery. Somatosensory evoked potential monitoring is not sensitive for the detection of subcortical ischemia and infarction in the distribution of the deep perforating arterial branches during intracranial aneurysm surgery. Although attenuation of loss of cortical SEP responses may indicate cerebral ischemia from inadequate collateral circulation during temporary arterial occlusion, normal SEPs can not exclude subcortical ischemia sufficient to cause significant postoperative deficits, and may therefore provide a false sense of security during these surgeries.

Adult↗
PubMed1997

Continuous electromyographic monitoring to detect nerve root injury during thoracolumbar scoliosis surgery.

STUDY DESIGN: The results of intraoperative monitoring during a case of nerve root injury sustained from scoliosis surgery to the thoracolumbar spine are described. OBJECTIVES: To improve the efficacy of intraoperative monitoring in preventing nerve root injury during scoliosis surgery. SUMMARY OF BACKGROUND DATA: Posterior tibial nerve somatosensory-evoked potentials are the electrophysiologic modality most commonly used for spinal cord monitoring during thoracolumbar spine surgery. Although radiculopathy is a more frequent postoperative complication than myelopathy, monitoring of mixed-nerve, somatosensory-evoked potentials may not detect injuries to individual nerve roots. METHODS: The patient described in this report developed left L5 radiculopathy after scoliosis surgery to the thoracolumbar spine. During surgery, intraoperative electromyographic monitoring identified frequent trains of neurotonic discharges in the left anterior tibial muscle. Bilateral, posterior, tibial nerve, somatosensory-evoked potentials remained normal. The left L5 nerve root was explored 9 days after the original surgery and was found to be compressed by bony structures. Electrophysiologic testing showed that the nerve root had undergone significant Wallerian degeneration, but remained in partial continuity. RESULTS: Nerve root injury was detected by neurotonic discharges identified during intraoperative electromyographic monitoring, but not by somatosensory-evoked potentials, which remained normal. When the injured nerve root was explored, a simple electromyographic technique was used to characterize the extent and type of injury. CONCLUSIONS: The authors of this study recommend electromyographic monitoring of appropriate lumbosacral myotomes in addition to somatosensory-evoked potentials during this type of procedure.

Adult↗
PubMed1997

Intraepidermal nerve fiber density in patients with painful sensory neuropathy.

Despite prominent symptoms of neuropathic pain, patients with small-fiber sensory neuropathies have few objective abnormalities on clinical examination and routine electrodiagnostic studies. We quantified intraepidermal nerve fiber (IENF) density in sections of skin obtained by punch skin biopsy, and found it to be significantly reduced in patients with painful sensory neuropathies compared with age-matched control subjects. In addition, IENF density correlated with clinical estimates of neuropathy severity, as judged by the extent of clinically identifiable sensory abnormalities. IENF density at the calf was lower than that obtained from skin at more proximal sites, indicating the length dependency of small-fiber loss in these neuropathies.

Adult↗
PubMed1996

A case of CNS cryptococcosis presenting with slowly alternating skew deviation.

Alternating skew deviation is a rare malfunction of vertical ocular motility, which has previously been described with lesions of the brainstem and cerebellum, although the precise localization is unknown. We describe an HIV seronegative patient with CNS cryptococcosis, whose initial presentation included slowly alternating skew deviation.

Adult↗
PubMed1994

Cytomegalovirus encephalitis in acquired immunodeficiency syndrome (AIDS).

Cytomegalovirus encephalitis (CMVE) is frequently diagnosed only at postmortem because its specific clinical features have not been fully identified. We have described the clinical, radiologic, and laboratory features of CMVE in a retrospective review of 14 autopsy-confirmed cases of CMVE and compared them with a control group of demented acquired immunodeficiency syndrome (AIDS) patients without CMVE. CMVE was more common among homosexual men, and a subacute onset was more typical (mean duration of presenting symptoms was 3.5 weeks versus 18 weeks in demented controls). Median survival times were 4.6 weeks for CMVE and 28 weeks for controls. CMVE was accompanied by prominent systemic CMV infection at autopsy, including CMV adrenalitis (92%), CMV pneumonitis (42%), systemic Mycobacterium avium intracellulare (MAI; 58%), and CMV retinitis (58%). Hyponatremia and MAI bacteremia were found in 58% of CMVE cases. Polymerase chain reaction (PCR) of CSF samples identified CMV genome in 33% of CMVE cases. CMVE was associated with periventricular enhancement on CTs and periventricular lesions with meningeal enhancement on MRI scans. CMVE should be particularly suspected in homosexual men presenting with subacute encephalopathy who have had AIDS for more than 1 year and have a history of systemic CMV infection. Other features supporting the diagnosis of CMVE include periventricular lesions, hyponatremia, and identification of CMV genome in CSF by PCR.

AIDS Dementia Complex↗