Characteristic evaluation of a Lithium-6 loaded neutron coincidence spectrometer.

Characteristics of a (6)Li-loaded neutron coincidence spectrometer were investigated from both measurements and Monte Carlo simulations. The spectrometer consists of three (6)Li-glass scintillators embedded in a liquid organic scintillator BC-501A, which can detect selectively neutrons that deposit the total energy in the BC-501A using a coincidence signal generated from the capture event of thermalised neutrons in the (6)Li-glass scintillators. The relative efficiency and the energy response were measured using 4.7, 7.2 and 9.0 MeV monoenergetic neutrons. The measured ones were compared with the Monte Carlo calculations performed by combining the neutron transport code PHITS and the scintillator response calculation code SCINFUL. The experimental light output spectra were in good agreement with the calculated ones in shape. The energy dependence of the detection efficiency was reproduced by the calculation. The response matrices for 1-10 MeV neutrons were finally obtained.

Distal accentuation of conduction slowing in polyneuropathy associated with antibodies to myelin-associated glycoprotein and sulphated glucuronyl paragloboside.

In four patients with a chronic, demyelinating polyneuropathy associated with monoclonal IgM antibodies to myelin-associated glycoprotein (MAG) and sulphated glucuronyl paragloboside (SGPG), we have observed a marked prolongation of distal motor latencies disproportionate to proximal segment-conduction velocities, in nearly all nerves studied. Distal accentuation of conduction slowing distinguished these patients from those with Charcot-Marie-Tooth polyneuropathy type 1A, chronic inflammatory polyneuropathy, and from controls, as demonstrated by regression of distal motor latency on proximal conduction velocity. Sixteen of 21 nerves (76%) studied in the patients with anti-MAG/SGPG polyneuropathy had a terminal latency index of < or = 0.25 versus 11 of 195 nerves (6%) of Charcot-Marie-Tooth polyneuropathy type 1A patients, three of 49 nerves (6%) of patients with chronic inflammatory polyneuropathy and none of the controls (P = 0.0001). Recognition of this unique pattern of generalized, distally predominant conduction slowing in anti-MAG/SGPG polyneuropathy may be useful in clinically distinguishing this from other chronic demyelinating polyneuropathies, and in possibly providing insights into the pathophysiology of this disorder.

Uniform slowing of conduction velocities in Charcot-Marie-Tooth polyneuropathy type 1.

We evaluated motor conduction studies in 129 patients with Charcot-Marie-Tooth disease type 1 (CMT1) to assess the uniformity of conduction slowing within individual patients. Conduction velocities were nearly identical in proximal and distal nerve segments (r = 0.86), from side to side (r = 0.95), in ipsilateral median and ulnar nerves (r = 0.94), and even in the median and peroneal nerves (r = 0.70). Segmental amplitude reductions suggestive of possible conduction block or differential dispersion were present in only 19 of 360 nerve segments studied (5.3%), and interphase cancellation or focal compression were likely alternative explanations in these cases. These findings support the concept that uniform conduction slowing characterizes CMT1, in distinction to acquired demyelinating polyneuropathies, which feature multifocal conduction abnormalities. We conclude that normal nerve conduction velocity in a single motor nerve can reliably exclude CMT1, but evaluation of several nerves and nerve segments to establish uniformity of conduction slowing is important in making this diagnosis. The homogeneity of the disturbance of nerve conduction favors a primary Schwann-cell disorder as the basis of CMT1.

Nerve conduction studies in Charcot-Marie-Tooth polyneuropathy associated with a segmental duplication of chromosome 17.

We evaluated motor conduction velocities in a large group of patients and their unaffected kin from five families in which a segmental duplication of chromosome 17p has shown complete linkage to Charcot-Marie-Tooth disease type 1 (CMT1A). Slowing of conduction was completely concordant with the presence of the segmental duplication; two clinically normal patients had slowed conduction. Nonetheless, among the patients with the CMT1A duplication, conduction velocities varied widely, by > 30 m/sec overall, by > 20 m/sec within families, and often by more than 10 m/sec between siblings and between parents and children. One patient was homozygous for the chromosome 17p duplication and had the slowest conduction velocity observed. Conduction slowing was not age-dependent and was present early in childhood. Our findings demonstrate complete penetrance at an early age of the electrophysiologic phenotype associated with the chromosome 17p duplication and confirm the reliability of nerve conduction studies in establishing the affection status in CMT1A. The great variation in conduction velocity among CMT1A patients emphasizes the influence of factors apart from the shared genetic mutation on phenotypic expression.

Conduction block as an early sign of reversible injury in ischemic monomelic neuropathy.

We report three patients with reversible motor conduction block in the forearm associated with ischemic monomelic neuropathy (IMN), which occurred in two patients following placement of brachial artery-cephalic vein shunts for hemodialysis. In the third patient, IMN resulted from spontaneous, probably embolic, brachial artery occlusion. Conduction block was observed shortly after the onset of symptoms, and preferentially involved the median nerve. Slowing of conduction velocity was seen in the same nerve segments. Electrophysiologic resolution, correlating with clinical improvement following treatment, occurred promptly in one patient and over several weeks in the others. Recognition of conduction block is important in the evaluation of IMN, and indicates the need for prompt treatment of likely reversible nerve injury.

Neuroprotective effects of glutamate antagonists and extracellular acidity.

Glutamate antagonists protect neurons from hypoxic injury both in vivo and in vitro, but in vitro studies have not been done under the acidic conditions typical of hypoxia-ischemia in vivo. Consistent with glutamate receptor antagonism, extracellular acidity reduced neuronal death in murine cortical cultures that were deprived of oxygen and glucose. Under these acid conditions, N-methyl-D-aspartate and alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate-kainate antagonists further reduced neuronal death, such that some neurons tolerated prolonged oxygen and glucose deprivation almost as well as did astrocytes. Neuroprotection induced by this combination exceeded that induced by glutamate antagonists alone, suggesting that extracellular acidity has beneficial effects beyond the attenuation of ionotropic glutamate receptor activation.

Antagonism of non-NMDA receptors augments the neuroprotective effect of NMDA receptor blockade in cortical cultures subjected to prolonged deprivation of oxygen and glucose.

A 30-60 min period of oxygen and glucose deprivation induced widespread degeneration of cultured murine neocortical neurons. Neuronal degeneration could be blocked by adding the selective NMDA antagonist MK-801 to the bathing medium; however, if the deprivation period was prolonged to 90-105 min, the neuroprotective effect of MK-801 was overcome. The non-NMDA antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) at 1-100 microM concentrations also failed to protect neurons against this prolonged insult, but the combination of CNQX with either MK-801 or D-APV produced marked neuroprotection. This synergistic action of CNQX was not due to enhanced blockade of NMDA receptors, as it was not mimicked by combining MK-801 with D-APV or 7-chlorokynurenate. These observations support the idea that combined NMDA and non-NMDA receptor blockade may have value in ameliorating the neuronal loss associated with prolonged ischemic insults in vivo.

Emergence of recreational drug abuse as a major risk factor for stroke in young adults.

OBJECTIVE: To investigate the clinical and epidemiologic relations between recreational drug abuse and stroke in young persons. DESIGN: A case-control study based on medical records. SETTING: San Francisco General Hospital, a 400-bed municipal hospital. PATIENTS: Consecutive sample of 214 patients aged 15 to 44 years, admitted between 1979 and 1988 with a diagnosis of ischemic or hemorrhagic stroke. An equal number of control patients admitted with diagnoses of status asthmaticus, acute appendicitis, or acute cholecystitis were matched to stroke patients by age, sex, and year of hospitalization. MEASUREMENTS AND MAIN RESULTS: Seventy-three patients with stroke (34%) were drug abusers compared with 18 (8%) of the controls. In 47 patients with stroke, temporal proximity of drug administration (n = 34) or infectious endocarditis (n = 13) suggested a direct association between drug abuse and stroke. After controlling for other identifiable stroke risk factors, the estimated relative risk for stroke among drug abusers compared with that among non-drug abusers was 6.5 (95% CI, 3.1 to 13.6), and this increased to 49.4 (CI, 6.4 to 379.0) for those patients whose symptoms began within 6 hours of drug administration. Among patients less than 35 years of age, drug abuse was the most commonly identified potential predisposing condition (47%), and it was the only condition with a significantly elevated relative risk for stroke (11.7; CI, 3.2 to 42.5). Further, a substantial rise in the proportion of drug-related strokes was observed in the last 3 years of the study (31% in 1986 to 1988, compared with 15% in 1979 to 1985, P = 0.008). Cocaine, especially recently, was the drug used most frequently in drug-related strokes. CONCLUSION: In an urban population such as ours, recreational drug abuse appears to be a prominent and growing risk factor for strokes in young adults.

New-onset seizures associated with human immunodeficiency virus infection: causation and clinical features in 100 cases.

PURPOSE: We attempt to define the significance and most common causes of new-onset seizures in patients with human immunodeficiency virus (HIV) infection. In addition, we review the seizure type, neurologic examination, and other clinical features to better address diagnostic and management issues in these patients. PATIENTS AND METHODS: We reviewed 100 cases of new-onset seizures in HIV-infected patients who underwent complete evaluations at the University of California, San Francisco, hospitals. RESULTS: Seizures were the presenting symptom of HIV-related illness in 18 patients, six of whom developed no other HIV-related illness until at least four months after the first seizure. Common causes in the 100 patients included mass lesions, HIV encephalopathy, and meningitis. No cause for the seizures was found in 23 patients despite a complete evaluation. An underlying cause was found in all patients with focal neurologic deficits but in only two of 24 who had normal results on an interictal neurologic examination. Focal ictal features were not predictive of cause. A cause was found in all 12 patients with status epilepticus or medically refractory seizures. A total of 12 of the 87 (14%) patients who received phenytoin developed a hypersensitivity reaction. Despite the brevity of follow-up in some patients, many patients, including those with no definable cause, had multiple seizures prior to the administration of anticonvulsants. CONCLUSION: The direct effects of HIV on the brain may be the single most common cause of seizures in this population. We favor treatment of a single seizure in patients with HIV infection.