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Biomedical subjects

R A Mackenzie

Publications and source records attributed to R A Mackenzie.

At least 19 recordsLinked to original sources
PubMed2003

Neuropsychological manifestations in a case of bilateral thalamic infarction.

Neuropsychological manifestation has been reported with lesions of the anterior and non-specific thalamic nuclei and mammilothalamic tract (MMT). These have been reported in the setting of arterial infarction and/or haemorrhage. Cerebral venous sinus thrombosis (CVT) is a rare cause of brain infarction. It occurs in the setting of oral contraceptive administration or pregnancy. Inherited thrombophilias are documented risk factors. The most frequent being heterozygous factor V Leiden mutation. We report a single case of bilateral thalamic infarction due to cerebral vein and sinus thrombosis. Clinically the case manifested with memory impairment and dysexecutive symptoms. Predisposing factor for venous thrombosis was a homozygous factor V Leiden mutation. The patient was treated with anticoagulation and made a good recovery.

Adult↗
PubMed2001

Beryllium-7 as a tracer of short-term sediment deposition and resuspension in the Fox River, Wisconsin.

Short-term (approximately monthly) sediment deposition and resuspension rates of surficial bed sediments in two PCB-laden impoundments on the Fox River, WI, were determined in the summer and fall of 1998 using 7Be, a naturally occurring radioisotope produced in the atmosphere. Decay-corrected activities and inventories of 7Be were measured in bed sediment and in suspended particles. Beryllium-7 activities generally decreased with depth in the top 5-10 cm of sediments and ranged from undetectable to approximately 0.9 pCi cm(-3). Inventories of 7Be, calculated from the sum of activities from all depths, ranged from 0.87 to 3.74 pCi cm(-2), and the values covaried between sites likely reflecting a common atmospheric input signal. Activities of 7Be did not correlate directly with rainfall. Partitioning the 7Be flux into "new" and "residual" components indicated that net deposition was occurring most of the time during the summer. Net erosion, however, was observed at the upstream site from the final collection in the fall. This erosion event was estimated to have removed 0.10 g (cm of sediment)(-2), corresponding to approximately 0.5 cm of sediment depth, and approximately 6-10 kg of polychlorinated biphenyls (PCBs) over the whole deposit. Short-term accumulation rates were up to approximately 130 times higher than the long-term rates calculated from 137Cs profiles, suggesting an extremely dynamic sediment transport environment, even within an impounded river system.

Beryllium↗
PubMed1999

An electroencephalographic investigation of late-onset schizophrenia.

We performed awake and resting electroencephalograms (EEGs) on 22 subjects with DSM-III-R schizophrenic disorder of late onset (at or after age 50 years), and compared them with the EEGs of 33 healthy community controls matched for age and gender. The EEGs were rated qualitatively and a 2-minute, artifact-free tracing from each subject was quantified manually by an experienced neurophysiologist unaware of the identity of the subject group. The only significant difference was the presence of more generalized slowing in the EEGs of schizophrenia patients, which was at least partially accounted for by the effect of neuroleptic drugs. The schizophrenic subjects did not have a greater prevalence of epileptiform disturbances or abnormal asymmetry of the EEG compared to the control group. Our study does not suggest the presence of underlying dementia in schizophrenia of late onset.

Age of Onset↗
PubMed1990

Surgery for refractory epilepsy.

Over a six-year period, 130 patients with medically intractable epilepsy were assessed for possible surgical treatment. Initial assessment comprised full neurological and neuropsychological examination, computed tomographic and magnetic resonance imaging brain scanning, and simultaneous video and surface plus sphenoidal electroencephalographic (EEG) recordings of typical seizures. Forty-one patients (32%) underwent further video and EEG recordings of their seizures with depth (intracerebral) or strip (subdural) electrodes. After these assessments 46 patients (35%) underwent surgery, and follow-up for six months to six years is reported in 41 patients. Of 30 patients who underwent temporal lobe surgery, 21 (70%) are free of seizures and four have had significant seizure reduction, meaning that 83% benefited from surgery. Optimal results were obtained for complex partial seizures when depth electrode recordings were obtained and when abnormal tissue was removed. Six extratemporal resections abolished seizures in two patients, and four others showed worthwhile improvement. Five patients underwent corpus callosotomy, resulting in a worthwhile improvement in three and modest improvement in two patients. No deaths or major complications occurred. It is concluded that surgical intervention can be beneficial for up to 30% of patients with medically intractable epilepsy, and referral of these patients to an appropriate institution is encouraged.

Brain↗
PubMed1989

Epilepsy surgery in Sturge-Weber syndrome.

A patient with Sturge-Weber syndrome developed seizures at the age of 4 years. At 13 years of age, she had intractable complex partial seizures with marked visual symptomatology. Interictal encephalograms showed bilateral slow activity, more marked over the right hemisphere with epileptogenic activity maximal in the right temporal region. Serial computerized axial tomography scans demonstrated evolution of bilateral occipital lesions with calcification and adjacent low density areas that were more marked on the right. Magnetic resonance imaging, angiography and neuropsychological evaluations were performed. An extensive resection of the right occipital lobe was achieved. One year after surgery, the patient has had seven brief seizures. Delineation of an epileptogenic focus and surgical removal of the lesion in patients with intractable seizures can now be considered in selected patients with bilateral central nervous system pathology.

Adolescent↗
PubMed1989

Selective epilepsy surgery in tuberous sclerosis.

A patient with tuberous sclerosis diagnosed at the age of 5 years developed an intractable seizure disorder characterized by complex partial seizures numbering 10-20/day. Interictal electroencephalograms (EEG) showed a right frontal epileptogenic focus. A computerized tomography scan demonstrated calcification in the right frontal region at two sites, periventricular calcification and multiple low density lesions. Neuropsychological assessment showed a verbal intelligence quotient (IQ) of 69 and a performance IQ of 88. Telemetry and video monitoring recorded 10 seizures during which the EEG showed flattening of ongoing sharp wave activity in the right frontal region. Electrocorticography further identified and localized epileptogenic tissue in the right frontal cortex and surgical removal of involved tissue and the adjacent two tubers was carried out. Twelve months after surgery the patient has had only two brief seizures.

Child, Preschool↗
PubMed1987

Postural stability and Colles' fracture.

We have tested the hypothesis that the Colles' fracture is due, not simply to bone loss at the menopause, but to postural instability in a subset of postmenopausal women such that they are rendered more liable to fall. We have measured bone mass by dual photon spinal densitometry and single photon wrist densitometry and measured postural sway in 19 postmenopausal women with a history of Colles' fracture. Our results show that not only do Colles' fracture subjects have a small reduction in bone mass but they have a significantly increased degree of postural sway, a finding which has previously been recognized to characterize older subjects with recurrent falls.

Accidental Falls↗
PubMed1987

Herpes zoster arteritis. Clinical and angiographic features.

Herpes zoster ophthalmicus is a common condition, and has now been widely recognised as associated with the delayed onset of neurological events, associated with angiographic evidence of arteritis. The time lag between the zoster and subsequent neurological symptoms, along with the age of the patients, often leads to a missed diagnosis. As more cases are recognised, the pathogenic mechanisms will be better characterised and treatment may become more effective.

Adult↗
PubMed1987

Herpes zoster arteritis: pathological findings.

This paper describes the pathological findings in two cases of delayed contralateral hemiparesis following herpes zoster arteritis. Both died of cerebral haemorrhage and a necrotizing angiitis was found involving the major vessels of the ipsilateral cerebral hemisphere. No feature of granulomatous arteritis or of encephalitis was found. It is likely that the virus spreads along intracranial branches of the ophthalmic nerve supplying the major arteries and causes the inflammatory reaction by direct invasion of vascular muscle.

Aged↗
PubMed1984

Evidence that halothane inhibits norepinephrine release from sympathetic nerve endings in dog saphenous vein by stimulation of presynaptic inhibitory muscarinic receptors.

Studies were done to determine the mechanism whereby halothane inhibits the release of norepinephrine from postganglionic sympathetic nerve endings. Helical strips of dog saphenous vein were mounted for superfusion and measurement of isometric contractile tension in the presence or absence of halothane (1.2 or 2.5%). Endogenous norepinephrine overflowing in response to electrical stimulation (10 V, 2 Hz for 15 min), and the content of norepinephrine remaining in the veins after stimulation, were measured by liquid chromatography with electrochemical detection. The data indicate that halothane decreased the stimulation-evoked release of norepinephrine by stimulation of prejunctional inhibitory muscarinic receptors. Evidence was also obtained that halothane may impair clearance of norepinephrine from the synaptic cleft.

Animals↗
PubMed1983

Neurophysiological evidence of aging in Down's syndrome.

Fifteen subjects with Down's syndrome had measurements of peripheral and central nervous system conduction parameters. Conventional nerve conduction studies revealed evidence of peripheral nerve dysfunction consistent with an axonal degeneration. Upper limb somatosensory evoked potentials were delayed compared with age-matched controls in both young and older age groups of Down's subjects. Lower limb somatosensory evoked potentials were also delayed when correction for height was made; furthermore the 'central conduction time' was prolonged in young and older groups. These results suggest that both peripheral and central nervous system function is impaired in Down's syndrome and the pattern of change is similar to that found with aging in normal individuals.

Adult↗
PubMed1981

Changes in peripheral and central nerve conduction with aging.

An electrophysiological study was made of 30 normal subjects aged 20 to 70 years. Routine methods were used to measure peripheral motor and sensory functions of the posterior tibial nerve. This nerve was then stimulated at the ankle and recordings made simultaneously over the thoraco-lumbar spine, cervical spine and central sensory cortex. Peripheral and central potentials were reproducibly recorded at each site in all subjects. Peripheral nerve motor and sensory potential amplitudes fell significantly with age, as did the amplitude of the thoraco-lumbar potential. Cervical and central potential amplitudes did not change significantly with age. The peak latencies of thoraco-lumbar, cervical and central potentials all showed a significant increase with age. In addition, when 'central conduction time' was calculated by subtracting thoraco-lumbar or cervical latency from the latency of the cortical potential, a significant prolongation with increasing age was still seen, especially in more rostral pathways.

Adult↗
PubMed1981

Familial occurrence of meningioma: a case report.

A father and daughter were each found to have an olfactory groove meningioma. No members of the family were found to have neurofibromatosis. There have been 4 previous reports of meningiomas occurring in families, and the present report adds support to the hypothesis that meningioma can be a heredofamilial disorder.

Adult↗