Subepithelial infiltrates in Acanthamoeba keratitis

Six patients had Acanthamoeba keratitis that manifested an unusual type of subepithelial corneal infiltrate late in the course of the disease. These infiltrates occurred in the anterior corneal stroma, often in a location removed from the site of infection. In four of these patients the infiltrates occurred with no other clinical signs of inflammation. Two patients had mild foreign-body sensation that resolved despite the persistence of the subepithelial infiltrates. The infiltrates resolved with topical corticosteroid therapy in three patients; however, in two of these three patients the infiltrates recurred when corticosteroid therapy was tapered or discontinued. The subepithelial infiltrates appeared and behaved similarly to those associated with viral and chlamydial corneal infections. An immunologic mechanism may be responsible for these unusual delayed-in-onset infiltrates.     

Variations in ambulatory test use: what do they mean?

This article discusses the meaning of variations in ambulatory test use with emphasis on practice setting, availability of testing services, financial incentives, and physician and patient characteristics.     

A new rapid and reproducible homologous immunoradiometric assay for amino-terminal parathyroid hormone in the rat

Measurement of parathyroid hormone (PTH) in the rat is most often performed with competitive ligand radioimmunoassays (RIA) utilizing heterologous antibodies. We report here the validation of a newly developed homologous immunoradiometric assay (IRMA) for rat PTH. Two different goat antibodies to the amino-terminal sequence of rat PTH are utilized; one is immobilized onto plastic beads to capture the PTH molecules and the other is radiolabeled for detection. To test this new IRMA, 30 Sprague-Dawley rats were randomized into three treatment groups to receive by intraperitoneal injection: (1) saline 1 ml/kg (control); (2) calcium chloride 40 mg/kg (hypercalcemic); and (3) EDTA 300 mg/kg (hypocalcemic). Blood samples were taken at 0, 30, 60, 180, and 300 minutes after administration of the assigned treatment for measurement of ionized calcium (Ca²⁺) and serum PTH. Most of the variance in PTH levels was found to be due to changes in Ca²⁺ (r²=0.780, P<0.0001). There was also a close temporal relationship between the two, with the highest levels of PTH occurring at the same measured time points as the lowest Ca²⁺, and vice versa. The measured detection limit of the IRMA was 3 pg/ml with intra-and interassay coefficients of variation of 1.74% and 3.07%, respectively. Serial dilutions with pooled rat serum, synthetic rat PTH-(1–34), and synthetic human PTH-(1–34) showed good parallelism with increased specificity for the pooled and synthetic PTH, despite a degree of crossreactivity with hPTH. The assay is able to quantitate rapid changes in PTH, providing all the advantages of IRMA methodology including technical simplicity and speed of performance, and is likely to become a useful tool in investigations of bone, mineral, and renal homeostasis using the rat.Presented in abstract form at the Fifteenth Annual Meeting of the American Society for Bone and Mineral Research, September 1993, Tampa, FL.     

Spoiling of transverse magnetization in gradient-echo (GRE) imaging during the approach to steady state

The signal evolution behaviors and corresponding image appearances for different methods of spoiling or refocusing the transverse magnetization in short TR gradient-echo imaging during the approach to steady state were investigated experimentally and using computer simulations based on the Bloch equations. Specifically, ideally spoiled, gradient-spoiled, gradient-refocused, and RF-spoiled pulse sequence configurations were studied. This study showed that, for the gradient-spoiled configuration, the signal evolution is position and phase-encoding order-dependent and, under typical imaging conditions, can deviate substantially from the ideally spoiled signal evolution at some spatial positions, resulting in intensity banding image artifacts. For the gradient-refocused configuration, the signal evolution oscillates toward the steady state and, generally, does not closely approximate that of ideal spoiling, resulting in different image contrast or image blurring. Using RF spoiling, the signal evolution closely approximates the ideally spoiled case for flip angles less than approximately 20° and T₂ values of less than approximately 200 ms and results in relatively artifact-free images. Also, this study showed that, for RF spoiling, an RF-pulse phase-difference increment other than 117°, such as 84°, may be optimal for gradient-echo imaging during the approach to steady state.     

Brain Blood Flow Alterations Induced by Therapeutic Vagus Nerve Stimulation in Partial Epilepsy: I. Acute Effects at High and Low Levels of Stimulation

Summary: Purpose: Left cervical vagus nerve stimulation (VNS) decreases complex partial seizures (CPS) by unknown mechanisms of action. We hypothesized that therapeutic VNS alters synaptic activities at vagal afferent terminations and in sites that receive polysynaptic projections from these medullary nuclei.
Methods: Ten patients with partial epilepsy underwent positron emission tomographic (PET) measurements of cerebral blood flow (BF) three times before and three times during VNS. Parameters for VNS were at high levels for 5 patients and at low levels for 5. Resting BF measurements were subtracted from measurements during VNS in each subject. Subtraction data were averaged in each of 2 groups of 5 patients. t Tests were applied to BF changes in brain regions that receive vagal afferents and projections (significant at p < O.05, corrected for repeated measures).
Results: In both the low- and high-stimulation groups during VNS, brain BF was (a) increased in the rostral, dorsal-central medulla; (b) increased in the right postcentral gyrus, (c) increased bilaterally in the hypothalami, thalami, and insular cortexes, and in cerebellar hemispheres inferiorly; and (d) decreased bilaterally in hippocampus, amygdala, and posterior cingulate gyri. The high-stimulation group had greater volumes of activation and deactivation sites.
Conclusions: Our findings suggest that left cervical VNS acutely increases synaptic activity in structures directly innervated by central vagal structures and areas that process left-sided somatosensory information, but VNS also acutely alters synaptic activity in multiple limbic system structures bilaterally. These findings may reflect sites of therapeutic actions of VNS.