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Biomedical subjects

R C Wallace

Publications and source records attributed to R C Wallace.

At least 19 recordsLinked to original sources
PubMed2000

Identification of Mycobacterium avium DNA sequences that encode exported proteins by using phoA gene fusions.

SETTING: Mycobacterium avium is the major cause of disseminated infection in patients with late stage AIDS. OBJECTIVE: In order to identify M. avium genes that may be involved in bacterial uptake and intracellular survival, a phoA -based reporter system was used to identify genes that encoded surface-expressed or exported proteins. DESIGN: PhoA (alkaline phosphatase) is only active if the protein is exported across the cell membrane into the periplasm. Consequently, detectable PhoA activity requires the fusion of a promoterless phoA gene with a DNA fragment containing a functional promoter and export leader sequence. A M. avium promoter library was constructed in the phoA reporter plasmid pJEM11 and screened in M. smegmatis for expression of active PhoA. RESULTS: More than 100 independent PhoA(+)recombinants were isolated, of which 15 were sequenced. Most of these exhibited varying degrees of homology with published M. avium, M. tuberculosis, M. bovis and M. leprae sequences. Based on sequence homology, one M. avium sequence was identified as a homologue of the M. tuberculosis phosphate transport gene phoS2 (Ag88). Another M. avium sequence was homolog with a putative M. tuberculosis cutinase gene. Both of these M. avium genes were cloned and sequenced. Several other M. avium sequences were homologous with, as yet, unidentified M. tuberculosis genes. CONCLUSION: PhoA fusion technology is applicable to the study of atypical slow growing mycobacteria. Most of the M. avium exported proteins identified in this study are highly homologous with genes from M. tuberculosis and M. leprae. In addition, parallels in gene organization were identified between M. avium and members of the M. tuberculosis complex.

Alkaline Phosphatase↗
PubMed2000

Incidence of postangiographic abnormalities revealed by diffusion-weighted MR imaging.

BACKGROUND AND PURPOSE: Occasionally we have observed anecdotal cases of asymptomatic hyperintensities on diffusion-weighted MR (DW-MR) examinations of the brain of patients who previously underwent routine cerebral angiography. These observations, as well as MR imaging and transcranial Doppler data in the literature suggesting a high rate of procedure-associated emboli, raise concern regarding the underdiagnosis of asymptomatic focal infarction associated with cerebral angiography. In order to determine whether asymptomatic diffusion abnormalities are frequently associated with procedures, we prospectively obtained DW-MR images before and after routine cerebral angiography. METHODS: Twenty consecutive patients, who met protocol criteria and received a routine three- or four-vessel diagnostic cerebral angiogram at our institution, were evaluated. Using a Bayesian estimate to establish an upper bound for the incidence of an event with zero occurrences in a study sample, the study group size was selected to exclude a 10% incidence of abnormalities revealed by DW-MR imaging of patients who underwent previous cerebral angiography. Two neuroradiologists evaluated imaging studies. RESULTS: Neither clinical signs nor abnormalities on DW-MR images were found, which suggested no infarction after angiography in our patient sample. Based on this data, an upper bound of 9% (95% confidence) is predicted for the appearance of abnormalities revealed by DW-MR imaging after cerebral angiography. CONCLUSION: Cerebral angiography is associated with an incidence of asymptomatic cerebral infarction of no more than 9%. It well may be substantially lower than this estimate; a more accurate evaluation of the true incidence would require a significantly larger study population. This test provides a convenient noninvasive means of assessing procedure-related cerebral infarction, such as that which occurs after carotid endarterectomy or vascular angioplasty and stenting.

Adult↗
PubMed1998

Brain arteriovenous malformations.

The diagnostic evaluation of a brain arteriovenous malformation requires a thorough understanding of the imaging features seen on CT, MR, and conventional angiography. Therapeutic planning requires a comprehensive understanding of the angioarchitecture of AVMs, necessitation selective and superselective angiography in order to give an accurate assessment of the lesion. This article will discuss the diagnostic work-up of AVMs. AVM treatment requires a multidisciplinary approach that includes interventional neuroradiology, radiosurgery, and neurosurgery. The considerations and philosophies of each discipline will discussed in order to provide the perspective required for the comprehensive treatment of AVMs.

Cerebral Angiography↗
PubMed1998

Retrospective blinded review of magnetic resonance imaging in patients with central electronystagmography findings.

OBJECTIVE: To evaluate the magnetic resonance imaging results (MRI) of patients with electronystagmography (ENG) suggestive of central vestibular dysfunction and to determine if MRI abnormalities correlate with ENG findings. STUDY DESIGN: Retrospective blinded case review. SETTING: A regional neurotology center. PATIENTS: Patients with ENG suggesting central vestibular dysfunction were identified (n = 30). An age-matched group of patients with normal ENG results were used as controls (n = 28). MAIN OUTCOME MEASURES: MRI abnormalities in cerebellum, brain stem, cerebellar peduncles, and central ENG findings. RESULTS: Twenty-one patients with abnormal MRI results of the vestibular pathway were found, 15 with abnormal and 6 with normal ENG results. MRI correlation with ENG findings has a better predictive value in older patients than in younger patients. Sixteen patients had MRI evidence of vascular compression, seven of whom had abnormal and nine of whom had normal ENG results. CONCLUSIONS: This study suggests that a detailed review of MRI images of the vestibular pathway is warranted, and, in patients with central ENG abnormalities, MRI may support the diagnosis of central vestibular dysfunction. MRI cannot support central vestibular dysfunction caused by vascular compression.

Adult↗
PubMed1997

Intra-arterial thrombolysis of embolic proximal middle cerebral artery occlusion from presumed atrial myxoma.

The role of thrombolysis in brain ischemia in patients with atrial myxoma is unknown. A patient with acute brain ischemia and previously undiagnosed atrial myxoma recanalized an occluded middle cerebral artery with intra-arterial thrombolysis. Arterial occlusion from presumed myxoma may be amenable to fibrinolysis. Angiography before treatment in patients with atrial myxoma excludes a myxomatous pseudoaneurysm and permits site-specific thrombolytic instillment.

Carotid Arteries↗
PubMed1997

Endovascular occlusion of the carotid or vertebral artery with temporary proximal flow arrest and microcoils: clinical results.

PURPOSE: To determine the clinical effectiveness of parent artery occlusion of the carotid or vertebral artery by means of temporary proximal flow arrest and microcoils. METHODS: Nineteen parent artery occlusions (15 carotid, four vertebral) were performed in 19 patients who successfully passed a balloon test occlusion. In these patients, endovascular occlusion of the carotid or vertebral artery was accomplished with the use of temporary proximal flow arrest and microcoils. RESULTS: All 19 parent arteries were occluded. Eighteen patients (95%) had good outcomes and one (5%) had a poor outcome. Fourteen patients (74%) had no complications and five (26%) had complications, of whom only one was left with a permanent neurologic deficit. Three (60%) of the complications were the result of delayed ischemic events after parent artery occlusion and were not predicted by balloon test occlusion. CONCLUSION: Endovascular occlusion with temporary proximal flow arrest and microcoils can be done effectively and successfully. The predictive value of the balloon test occlusion is the major complicating factor, as it is with balloon occlusion. This technique offers an additional tool that can be used for endovascular occlusion of the carotid or vertebral artery and seems to be less difficult technically. It is our primary technique for parent artery occlusion.

Adolescent↗
PubMed1997

Basilar artery rethrombosis: successful treatment with platelet glycoprotein IIB/IIIA receptor inhibitor.

We describe the use of abciximab to prevent rethrombosis of the basilar artery after transluminal angioplasty. A 60-year-old patient with vertebral basilar insufficiency and acute occlusion of the basilar artery underwent revascularization with urokinase and angioplasty. Despite the repeated use of urokinase and angioplasty under anticoagulation with heparin, the basilar artery immediately rethrombosed. In a final attempt to prevent rethrombosis, abciximab was administered before the final angioplasty, resulting in a widely patent basilar artery and no rethrombosis.

Abciximab↗
PubMed1996

Preliminary results of intracranial angioplasty for vascular stenosis caused by atherosclerosis and vasculitis.

PURPOSE: To evaluate the results of balloon angioplasty of 17 stenoses resulting from intracranial atherosclerosis and vasculitis. METHODS: Seventeen skull-base and intracranial lesions were dilated with a microballoon angioplasty catheter. RESULTS: Initially, 16 of the 17 stenoses showed improvement at angiography. Moderate residual stenosis was found in 2 of 12 atherosclerotic lesions, both in the distal vertebral artery. Angioplasty in 1 of 12 atherosclerotic lesions caused worsening of the stenotic site, also in the distal V4 region of the vertebral artery. All but one of the patients improved clinically. However, all five lesions caused by acute vasculitis progressed to occlusion after initial improvement. CONCLUSION: Intracranial percutaneous transluminal angioplasty is a viable nonsurgical option for the treatment of atherosclerotic vascular insufficiency, but it may not be as successful in treating lesions caused by vasculitis in the acute phase.

Aged↗
PubMed1995

Transient resolution of bilateral tremor after unilateral thalamotomy, associated with focal injury of the corpus callosum: case report.

We present a patient with Parkinson's disease whose bilateral tremor transiently resolved after a unilateral left ventrolateral thalamotomy. The transient resolution of the bilateral tremor was associated with a focal thalamic lesion and a second lesion in the corpus callosum. The mechanism of this phenomenon may be related to temporary disruption of descending bilateral corticostriate projections by the callosal lesion.

Corpus Callosum↗
PubMed1995

The safety and effectiveness of brain arteriovenous malformation embolization using acrylic and particles: the experiences of a single institution.

The purpose of this article is to report on the safety and effectiveness of brain arteriovenous malformation (AVM) embolization for two series of patients, of which one was treated with particulate embolization and the other with acrylic embolization. Sixty-five consecutive patients from embolization logs and patient records from 1988 to 1993 were reviewed. AVMs were routinely treated with particulate embolization early in the review (1988-1991), and after a transition period, the technique was changed to acrylic embolization for the remainder of the study period (1992-1993). All patients were treated with the ultimate goal of complete AVM obliteration. AVMs were embolized and resected, if possible, and if unresectable, they were reduced in size with embolization and radiated. The course of treatment for each patient was reviewed. The effectiveness at the end of treatment was analyzed for the ability to resect the AVM and, if unresectable, the ability to reduce the AVM to radiation size. Additionally, the safety of each embolization technique was evaluated in the context of comprehensive care, in terms of the safety of the procedure itself, the surgical resection after embolization, and the outcome at the end of comprehensive treatment. This article outlines the safety and effectiveness of acrylic and particulate embolization at a single institution. The ability to surgically resect an AVM after embolization and to reduce nidus size with acrylic was at least comparable with that with particulate embolization. Comprehensive complication rates were lower after acrylic embolization and were heavily influenced by a decreased number of surgical complications in the acrylic series. These data support the need to conduct a randomized prospective clinical trial to compare the relative safety and effectiveness of the two methods of embolization.

Acrylic Resins↗
PubMed1994

Efficacy of endovascular treatment of meningiomas: evaluation with matched samples.

PURPOSE: To evaluate the clinical efficacy, cost-effectiveness, and safety of presurgical devascularization of meningiomas. METHODS: Matched samples of embolized and nonembolized groups of meningiomas were compared. The study variables for clinical efficacy were estimated blood loss, number of transfusions, surgical resection time, and length of hospitalization. The cost-effectiveness was evaluated by adjusting all hospital costs to 1991 dollar amounts, and adding additional embolization costs and fees to the hospital cost totals for the embolized group. A qualitative comparison of complications was made. RESULTS: All dependent variables evaluating the clinical efficacy of the procedure (estimate blood loss, 533 cc versus 836 cc; number of transfusions, 0.39 units versus 1.56 units; surgical resection time, 305.8 minutes versus 337.5 minutes; and length of hospitalization, 10.6 days versus 15.0 days) displayed trends of higher means in the nonembolized group; however, only the estimated blood loss and number of transfusions variables were significant. The cost-effectiveness of the procedure was not statistically significant. The mean cost was $29,605 for the embolized group and $38,449 for the nonembolized group. There were three major and nine minor complications in the nonembolized group and zero major and six minor complications in the embolized group. There were four additional minor complications caused by the embolization procedure. CONCLUSION: Endovascular devascularization of meningiomas is beneficial for large meningiomas because it diminishes the necessity of intraoperative transfusions and decreases blood loss. The additional day of hospitalization, emolization costs, and costs of complications do not conversely increase treatment costs. There were no major complications or adverse long-term effects caused by the embolization procedure.

Blood Loss, Surgical↗
PubMed1991

Intracranial tuberculosis in children: CT appearance and clinical outcome.

We retrospectively evaluated the CT studies of 9 children who presented with intracranial tuberculosis during 1981-1987, and compared their radiographic appearance with the clinical outcome. The most common radiographic findings were: 1) ventriculomegaly (7/9) ,2) tuberculoma formation (6/9), and 3) infarction (4/9). Of 7 patients with ventriculomegaly, 3 required a ventricular shunt and 2 had spontaneous resolution of ventricular dilatation. Four children with ventriculomegaly were moderately or severely retarded, one had cognitive dysfunction, and one was neurologically normal. Four of six children with tuberculoma also had infarction and/or ventriculomegaly; of these four children, three were moderately or severely retarded. Two patients with tuberculoma as the only intracranial abnormality had complete resolution of the granuloma with normal neurologic outcome following antituberculous therapy. The four children with large vessel infarction also had ventriculomegaly; three had poor clinical outcome. The presence of tuberculoma alone is not necessarily predictive of poor neurologic outcome; age less than 20 months, infarct, and/or ventriculomegaly are usually associated with sequelae.

Cerebral Infarction↗
PubMed1990

An improved assay for human tetanus anti-toxin and its use in the accession of human plasma for the production of high-titre tetanus immunoglobulin.

A simplified passive haemagglutination (PHA) screening test, an improved quantitative PHA assay, and a stable test cell preparation are described, as well as a comprehensive testing strategy which have been used in concert at this Service over the past 10 years for the successful accession of high-titre tetanus anti-toxin (TAT) plasma for fractionation into human tetanus immunoglobulin (HTIG). The sequential deployment of the screening and quantitative assays, has permitted large numbers of donors to be screened quickly and economically, and has helped establish a significant core of regular donors with high TAT levels. The assays have proven to be highly sensitive and specific and relatively simple to perform, while the coated cells are inexpensive and easily prepared. Approximately 20% of donors screened from the Sydney metropolitan area had TAT levels of 3 IU/ml or greater.

Evaluation Studies as Topic↗
PubMed1990

Experience of a molecular genetics service in prenatal diagnosis by DNA analysis.

Prenatal diagnoses of the genetic disorders alpha, beta thalassemia, HbS, Hb Lepore, hemophilia and cystic fibrosis were sought in 88 cases. Six unsuccessful attempts at diagnosis resulted from DNA polymorphisms which were only 50% informative (four cases) and prenatal diagnoses which had been undertaken before it was known whether DNA polymorphisms in family studies were informative (two cases). The most frequent indications for prenatal diagnosis were the hemoglobinopathies although requests for exclusion of cystic fibrosis formed the majority during 1989. Strong linkage disequilibrium between the cystic fibrosis defect and its associated DNA polymorphisms facilitated detection of this disorder. Late presentations among patients with beta thalassemia and hemophilia and the necessity for more specialised genetic counselling were the commonest problems encountered.

Chromosome Mapping↗
PubMed1989

Hypoxanthine-guanine phosphoribosyltransferase deficiency in three brothers with gout: characterization of a variant, HPRTEdinburgh, having altered isoelectric point, increased thermal lability and normal levels of messenger RNA.

Three brothers who developed acute gouty arthritis at ages 16, 20 and 26 years were found to have increased plasma urate. Erythrocyte hypoxanthine phosphoribosyltransferase (HPRT) activity was less than 1% of normal and adenine phosphoribosyltransferase (APRT) activity was increased 2-3-fold. This variant, HPRTEdinburgh, was further studied using lymphoblast lines established from these patients and the following observations are consistent with a mutation involving a single amino acid substitution. Lymphoblasts from these patients had 0.9-1.6% of control HPRT activity which was 8-fold more labile than control activity at 75 degrees C. Isoelectric focusing of the variant protein in polyacrylamide gels indicated a pI of 6.5-6.7 which is more basic than normal HPRT, pI 6.0-6.3. The Michaelis constants were increased: 10-fold for hypoxanthine from 1.3 to 13 mumol/L, and 5-fold for PP-ribose-P from 6 to 30 mumol/L, for control and variant respectively. The Ki for product inhibition by GMP was marginally increased in the variant. Northern blot analysis of variant lymphoblast RNA indicated normal amounts of the expected 1.6 kilobase messenger RNA.

Adolescent↗