A highly specific inhibitor of human p38 MAP kinase binds in the ATP pocket

The crystal structure of human p38 mitogen-activated protein (MAP) kinase in complex with a potent and highly specific pyridinyl-imidazole inhibitor has been determined at 2.0 A resolution. The structure of the kinase, which is in its unphosphorylated state, is similar to that of the closely-related ERK2. The inhibitor molecule is bound in the ATP pocket. A hydrogen bond is made between the pyridyl nitrogen of the inhibitor and the main chain amido nitrogen of residue 109, analogous to the interaction from the N1 atom of ATP. The crystal structure provides possible explanations for the specificity of this class of inhibitors. Other protein kinase inhibitors may achieve their specificity through a similar mechanism. The structure also reveals a possible second binding site for this inhibitor, with currently unknown function.

Effects of log P and phenyl ring conformation on the binding of 5-phenylhydantoins to the voltage-dependent sodium channel

Binding to the neuronal voltage-dependent sodium channel (NVSC) was evaluated for 12 5-phenylhydantoins which systematically varied either log P and/or 5-phenyl ring orientation. The linear correlation of log P with in vitro sodium channel binding activity (log IC50) for hydantoins 1-12 and diphenylhydantoin (DPH) (r2 = 0.638) suggested that simple partitioning into the lipid phase is important but not sufficient to account for the effects of hydantoins on the NVSC. Comparisons among different hydantoins with the same log P but different low-energy phenyl ring orientations revealed that, in addition to log P, the correct 5-phenyl orientation is important for efficient binding.

Crystallization and preliminary crystallographic analysis of recombinant human P38 MAP kinase

The recombinant human p38 MAP kinase has been expressed and purified from both Escherichia coli and SF9 cells, and has been crystallized in two forms by the hanging drop vapor diffusion method using PEG as precipitant. Both crystal forms belong to space group P2(1)2(1)2(1). The cell parameters for crystal form 1 are a = 65.2 A, b = 74.6 A and c = 78.1 A. Those for crystal form 2 are a = 58.3 A, b = 68.3 A and c = 87.9 A. Diffraction data to 2.0 A resolution have been collected on both forms.

Cost of care for cancer in a health maintenance organization

The direct costs of medical care for cancer are examined at Kaiser Permanente (KP) in Northern California. Use data from July 1987 through June 1991 were obtained from KP automated files for all 21,977 KP patients in the Bay Area SEER registry with cancer at one of seven cancer sites. Medical charts were reviewed for a stratified sample of 886 patients. Costs were estimated for initial, continuing, and terminal care, and for all person time within 15 years of diagnosis, by stage at diagnosis. From diagnosis until death or 15 years, long-term costs attributable to cancer were as follows: breast, $35,000; colon, $42,000; rectum, $51,000; lung, $33,000; ovarian, $64,000; prostate, $29,000; and Non-Hodgkin's Lymphoma (NHL), $48,000. The utilization and cost results reported here may be useful in assessing the cost-effectiveness of cancer prevention and control programs, in adjusting capitation rates and budgets, and in estimating the aggregate medical care costs attributable to cancer.

Changes in lung volume and volume of emphysema after unilateral lung reduction surgery: analysis with CT lung densitometry

PURPOSE

To evaluate changes in volume of the lungs and volume of emphysema after unilateral lung reduction surgery (ULRS) by using computed tomographic (CT) lung densitometry.

MATERIALS AND METHODS

Twenty-eight patients underwent CT before and 3 months after ULRS. With use of a density mask software program and a three-dimensional graphics workstation, CT scans were analyzed to define the volume of the lungs and the volume of emphysema. Pre- and postoperative mean CT numbers were determined.

RESULTS

After ULRS, the surgically reduced lung volume decreased 22%, and the intact opposite lung volume increased 4%. Emphysema in the surgically reduced lung decreased 14% and was unchanged in the intact opposite lung. Mean CT numbers in the surgically reduced lung increased 26 HU but were unchanged in the intact opposite lung.

CONCLUSION

The effects of ULRS on each lung can be evaluated by using CT lung densitometry and a three-dimensional graphics workstation. ULRS reduces emphysema and lung volume in the surgically reduced lung without statistically significant worsening of contralateral emphysema at 3 months.

Protein and DNA requirements for the transcription factor IIIA-induced distortion of the 5 S rRNA gene promoter

Transcription factor-induced DNA distortion has become a common theme in eukaryotic gene regulation. A number of techniques have been applied to the study of transcription factor-induced DNA bending and flexibility including electron microscopy, circular permutation gel analysis, helical phasing gel analysis and cyclisation kinetics in solution. We have applied these techniques in order to assess the role that specific DNA sequences and protein domains of transcription factor IIIA (TFIIIA) play in the TFIIIA-induced distortion of the Xenopus 5 S ribosomal RNA gene promoter. Electron spectroscopic imaging analysis of TFIIIA:DNA complexes indicate that TFIIIA binding involves compaction of the 5 S promoter into a precise three-dimensional hairpin-shaped structure. This compaction can be detected utilising circular permutation gel analysis and the distortion results in an apparent bend angle of 55 to 60 degrees near the centre of the TFIIIA binding site. Helical phasing analysis demonstrates that the 60 degrees bend angle as measured by circular permutation can be detected as a static bend directed towards the minor groove between bases +63 and +64 of the 5 S rRNA gene. The amplitude of the TFIIIA:5 S gene phasing signal is similar to the phasing signal obtained utilising bacterial CAP:DNA complexes with bend angles of approximately 90 degrees. These results are supported by phased ligase-mediated cyclisation kinetics in solution. Analysis of DNA deletion constructs indicate that the 5' A block of the internal 5 S gene promoter, which is required for transcriptional activity, is also required for TFIIIA-induced distortion of the 5 S gene promoter. Analysis of the N-terminal papain fragment of TFIIIA indicates that the 34 kDa zinc finger DNA binding domain is sufficient for compaction of the 5 S gene promoter. These results are discussed in relation to the modular model of TFIIIA:DNA interaction in which individual zinc fingers contribute to the protein-induced distortion of the DNA helix and overall DNA binding affinity in a complex, non-additive fashion.

Parathyroid adenomas: accurate detection and localization with Tc-99m sestamibi SPECT

PURPOSE

To evaluate the ability to detect and localize parathyroid adenomas with technetium-99m sestamibi single photon emission computed tomography (SPECT).

MATERIALS AND METHODS

Forty-seven adult patients underwent Tc-99m sestamibi SPECT. Early (15-30 minutes after injection) and delayed (2-4 hours after injection) images were acquired. Thirty-three patients were examined for initial parathyroid surgery; the remaining 14, for repeat surgery because of persistent or recurrent hyperparathyroidism. SPECT reprojection images viewed in a rotating cine-display mode were read independently by two nuclear medicine physicians who were blinded to the results of other localization studies. Thirty-seven patients underwent subsequent neck exploration. SPECT findings were compared with surgical and histopathologic findings.

RESULTS

In the 37 patients who underwent surgery, parathyroid adenomas were confirmed in 34 (92%) and hyperplasia in three (8%). In 31 patients, adenomas were correctly detected and localized with early SPECT images (sensitivity, 91%). In contrast, the sensitivity of delayed SPECT images was 74% (25 of 34 patients) for detection and 32% (11 of 34 patients) for localization. Early SPECT images were significantly better for localization (P < .001) and detection (P = .03).

CONCLUSION

For Tc-99m sestamibi parathyroid imaging, early SPECT images were the most accurate in the detection and localization of parathyroid adenomas.

Prostanoid production in rabbit corpus cavernosum. II. Inhibition by oxidative stress

PURPOSE

To investigate the effects of reoxygenation following hypoxia on prostanoid production in rabbit penile corpus cavernosum tissue (RCC) in organ culture.

MATERIALS AND METHODS

Strips of RCC were incubated in organ culture media under either 21% O2 (control, PO2 approximately 167 mm.Hg) or 0% O2 (hypoxia, PO2 approximately 27 mm.Hg) followed by a reoxygenation period with 21% O2, in the presence or absence of exogenous arachidonate, Tiron or catalase. Prostanoids were measured in collected media by radioimmunoassay. Malondialdehyde levels were measured in RCC following exposure to either control or hypoxia-reoxygenation conditions.

RESULTS

Under hypoxic conditions, basal release of prostanoids (PGI2, PGF2 alpha, PGE2 and TXB2) was inhibited. Although this inhibition was reversible upon reoxygenation, the recovery was delayed, requiring at least 2 hours of exposure to 21% oxygen to reestablish prostanoid production. Reoxygenation also caused lipid peroxidation as measured by an increase in malondialdehyde levels. When reoxygenation was done in the presence of exogenous arachidonate, recovery of PGI2 production was complete by 1 hour. Reoxygenation in the presence of a scavenger of reactive oxygen species (Tiron) or catalase significantly improved the recovery rate of PGI2 production.

CONCLUSIONS

These results show that reoxygenation of hypoxic tissue generates oxidative stress that interferes with the recovery of prostanoid production by alteration of a biosynthetic point(s) upstream from prostaglandin H synthase (PGHS) including, at least, phospholipid peroxidation.

Prostanoid production in rabbit corpus cavernosum: I. regulation by oxygen tension

PURPOSE

To investigate the effects of oxygen tension on prostanoid synthesis in rabbit penile corpus cavernosum tissue (RCC) in organ culture.

MATERIALS AND METHODS

Strips of rabbit corpus cavernosum were incubated in organ culture media under varying oxygen conditions (0%, 12% and 21% oxygen), in the presence or absence of acetylcholine and arachidonate stimulation. Prostanoids were measured in collected media by radioimmunoassay. Prostaglandin H synthase (PGHS) protein levels and mRNA PGHS expression were measured under both 0% and 21% oxygen conditions.

RESULTS

Basal and acetylcholine-stimulated PGI2 release was progressively diminished as a function of diminishing oxygen tension (pO2 from approximately 165 to 25 mm.Hg). The basal and stimulated production of other prostanoids, thromboxane A2, PGF2alpha, and PGE2, was also significantly inhibited under 0% oxygen (approximately 25 mm.Hg) conditions. However, incubation under 0% oxygen did not alter PGHS protein levels nor mRNA PGHS expression. Cavernosal strips incubated under 0% oxygen but supplemented with exogenous arachidonate (10 microM.) maintained significantly lower PGI2 production than tissues exposed to 21% oxygen (approximately 165 mm.Hg).

CONCLUSIONS

These data demonstrate that oxygen tension regulates prostaglandin production in corporal tissue. The reduction in prostanoid production during hypoxia can be attributed to inhibition of PGHS activity rather than the expression of the enzyme. In view of the role of PGI2 as an inhibitor of platelet aggregation and white cell-endothelial adhesion, our findings may provide mechanistic insight into the alteration in corporal blood homeostasis ischemic-hypoxic priapism.

Improvement in pulmonary function and elastic recoil after lung-reduction surgery for diffuse emphysema

BACKGROUND

Pulmonary function may improve after surgical resection of the most severely affected lung tissue (lung-reduction surgery) in patients with diffuse emphysema. The basic mechanisms responsible for the improvement, however, are not known.

METHODS

We studied 20 patients with diffuse emphysema before and at least three months after either a unilateral or a bilateral lung-reduction procedure. Clinical benefit was assessed by measurement of the six-minute walking distance and the transitional-dyspnea index, which is a subjective rating of the change from base line in functional impairment and the threshold for effort- and task- dependent dyspnea. Pressure-volume relations in the lungs were measured with static expiratory esophageal-balloon techniques, and right ventricular systolic function was assessed by echocardiography.

RESULTS

The patients had significant improvement in the transitional-dyspnea index after surgery (P<0.001). The mean (+/-SD) coefficient of retraction, an indicator of elastic recoil of the lung, improved (from 1.3+/-0.6 cm of water per liter before surgery to 1.8+/-0.8 after, P<0.001). Sixteen patients with increased elastic recoil had a greater increase in the distance walked in six minutes than the other four patients, in whom recoil did not increase (P=0.02). The improved lung recoil led to disproportionate decreases in residual volume as compared with total lung capacity (16 percent vs. 6 percent), but the decreases in both values were significant (P<0.001). Forced expiratory volume in one second increased (from 0.87+/-0.36 to 1.11+/-0.45 liters, P<0.001). End-expiratory esophageal pressure also decreased (P=0.002). These improvements in lung mechanics led to a decrease in arterial partial pressure of carbon dioxide form 42+/-6 to 38+/-5 mm Hg (P=0.006). Furthermore, the fractional change in right ventricular area, an indicator of systolic function, increased from 0.33+/-0.11 to 0.38+/-0.010 (P=0.02).

CONCLUSIONS

Lung-reduction surgery can produce increases in the elastic recoil of the lung in patients with diffuse emphysema, leading to short-term improvement in dyspnea and exercise tolerance.

Prostanoid production in rabbit corpus cavernosum: I. regulation by oxygen tension

PURPOSE

To investigate the effects of oxygen tension on prostanoid synthesis in rabbit penile corpus cavernosum tissue (RCC) in organ culture.

MATERIALS AND METHODS

Strips of rabbit corpus cavernosum were incubated in organ culture media under varying oxygen conditions (0%, 12% and 21% oxygen), in the presence or absence of acetylcholine and arachidonate stimulation. Prostanoids were measured in collected media by radioimmunoassay. Prostaglandin H synthase (PGHS) protein levels and mRNA PGHS expression were measured under both 0% and 21% oxygen conditions.

RESULTS

Basal and acetylcholine-stimulated PGI2 release was progressively diminished as a function of diminishing oxygen tension (pO2 from approximately 165 to 25 mm.Hg). The basal and stimulated production of other prostanoids, thromboxane A2, PGF2alpha, and PGE2, was also significantly inhibited under 0% oxygen (approximately 25 mm.Hg) conditions. However, incubation under 0% oxygen did not alter PGHS protein levels nor mRNA PGHS expression. Cavernosal strips incubated under 0% oxygen but supplemented with exogenous arachidonate (10 microM.) maintained significantly lower PGI2 production than tissues exposed to 21% oxygen (approximately 165 mm.Hg).

CONCLUSIONS

These data demonstrate that oxygen tension regulates prostaglandin production in corporal tissue. The reduction in prostanoid production during hypoxia can be attributed to inhibition of PGHS activity rather than the expression of the enzyme. In view of the role of PGI2 as an inhibitor of platelet aggregation and white cell-endothelial adhesion, our findings may provide mechanistic insight into the alteration in corporal blood homeostasis ischemic-hypoxic priapism.

New curriculum challenges in health administration education

Tradition curriculum content and structure in health administration education programs have focused on the managing of individual institutions, the business function, and the hospital as the center of the health system. These assumptions are challenged by managed care, with its orientation on integrating the business and clinical functions; prevention and primary care; and the provision of services through integrated service networks. The design and process of curriculum change in response to new organization structures and management challenges are explored.

H2-M3wt-restricted, Listeria monocytogenes-specific CD8 T cells recognize a novel, hydrophobic, protease-resistant, periodate-sensitive antigen

Mice infected with Listeria monocytogenes (LM) generate H2-M3wt-restricted CD8 effectors which recognize a heat-killed LM-associated antigen (HAA) presented by macrophages. To characterize HAA, we extracted a bioactive component from LM using SDS or NaOH. Extracted HAA aggregated in hydrophilic solvents but dissociated in the presence of SDS into a smaller subunit which migrated in Sephadex G-200 between chymotrypsinogen (25 kDa) and cytochrome c (12.5 kDa). HAA bioactivity and size was unaffected by proteinase K under conditions which degraded virtually all detectable protein. HAA was also unaffected by other proteases, RNase and DNase, but HAA bioactivity was destroyed by periodate, an agent that degrades carbohydrates. These studies demonstrate that H2-M3wt can present a hydrophobic, non-peptide, microbial antigen, probably glycolipid in origin, to CD8 T cells.

The effects of acute exercise on gallbladder function in an adult female population

It has been suggested that aerobic exercise influences gallstone disease pathogenesis through its effects on gallbladder motility. The purpose of the present investigation was to examine the effects of acute aerobic exercise on gallbladder emptying. Gallbladder function was evaluated, via cholescintigraphy, in 12 healthy females after undergoing two experimental trials [i.e., postprandial (P) and exercise + postprandial (E + P))]. In the E + P trial, 60 min after injection of 99mTc disofenin, subjects exercised for 30 min at 65.3 +/- 0.9%, (mean +/- SEM) of VO2 peak on a recumbent leg ergometer, and then ingested 8 oz of a liquid meal to promote gallbladder emptying. In the P trial the meal was administered at the same time relative to the E + P trial; however, for the 30 min prior to meal ingestion subjects remained in a resting supine position. Postprandial gallbladder ejection fraction (EF) was nonsignificantly higher in the E + P trial (49.4 +/- 5.1%) than in the P trial (46.6 +/- 6.7%). Results of this study also indicated that during a fasted state the gallbladder undergoes significant periods of spontaneous emptying both at rest EF = 25 +/- 5.6% (P < 0.02) and during exercise EF = 17 +/- 4.3% (P < 0.01). In conclusion, the results of this study indicate that 30 min of aerobic exercise at 65% of VO2 peak does not effect gallbladder motility in a healthy, premenopausal, female population.

Use of gene tests to detect hereditary predisposition to cancer: what do we know about cost effectiveness?

Mutations in 4 genes associated with DNA repair have been shown to be associated with hereditary non-polyposis colon cancer (HNPCC) in families which display unusually high risk for colorectal cancer. Laboratory tests for mutations in these genes will soon be commercially available, raising the possibility that population-wide gene testing to identify individuals with an inherited susceptibility to colorectal cancer could be conducted. The purpose of our report is to explore the economic implications of conducting a program of population-wide screening for HNPCC compared with alternative programs which would be restricted to families already known to be at high risk for HNPCC. Rather than provide a definitive answer to these questions, our purpose is to indicate priority areas of research which need to be conducted before such a definitive analysis can be done. An exploratory analysis has been conducted to determine which factors are most important in determining the cost-effectiveness of a genetic testing program for HNPCC. The base case analysis focuses on current uncertainty about the population prevalence of the HNPCC genotype and phenotype, factors which are central to the cost-effectiveness of population-wide screening. Uncertainty in parameters related to the cost and effectiveness of screening and preventive interventions for HNPCC were explored using additional sensitivity analyses. Favorable levels of cost-effectiveness for population-wide screening are achieved only when the most favorable assumptions about HNPCC prevalence and the cost and effectiveness of screening and preventive interventions are made.

Unilateral thoracoscopic surgical approach for diffuse emphysema

We evaluated the use of a lateral thoracoscopic approach for lung reduction surgery in patients with diffuse emphysema. Sixty-seven patients with a mean age of 61.9 years underwent operation. Operative side was determined by preoperative imaging. The procedures were laser ablation in 10 patients and stapler resection in 57 patients. Ten patients, including six of the 10 patients in the laser-only group had poor outcome (death or hospitalization longer than 30 days), leading us to abandon the laser technique. Of the remaining 57 patients undergoing primary stapled resection, duration of chest tube placement averaged 13 days (range 3 to 53 days) with a mean hospital stay of 17 days (range 6 to 99 days). Seven patients required ventilation for longer than 72 hours, six patients underwent conversion of the procedure to open thoracotomy, four patients acquired arrhythmias, and three patients were treated for empyema. There was one early death (1.7%), from cardiopulmonary failure. Forty patients returned for 3-month evaluation. Significant (p < 0.0001) improvements were seen in forced vital capacity (2.69 L after vs 2.26 L before) and forced expiration volume in 1 second (1.04 L after vs 0.82 L before), with 25 of 40 patients (63%) showing an improvement of more than 20%. Lung volume measures, in particular residual volume, fell significantly. Arterial blood gas analysis revealed that carbon dioxide tension fell significantly in patients with preoperative hypercapnia (carbon dioxide tension > 45 mm Hg, p = 0.018). Six-minute walk test results improved (894 feet after vs 784 feet before, p = 0.002), and symptomatic benefit was confirmed by significant improvement in the dyspnea index. The combination of both hypercapnia and reduced single-breath diffusing capacity for carbon monoxide was significantly more frequent (p = 0.0026) and was 86% specific (5 of 6 patients) in predicting serious postoperative risk. We conclude that the lateral thoracoscopic surgical approach to diffuse emphysema offers significant improvement in pulmonary mechanics and functional impairment. Patients with a combination of hypercapnia and reduced single-breath diffusing capacity for carbon monoxide should not be considered for this procedure because of significant perioperative risk.

Breast cancer control among the underserved--an overview

This paper explores barriers to the use of standard screening and breast cancer treatment that result in systematic differences in health outcomes. We review available data on individual, socioeconomic, and health system determinants of access to standard breast cancer care, including screening, diagnostic, and treatment services. Based on this review, we discuss the combination of factors which result in underservice. We argue that a broad framework which considers health system and social class as well as individual factors is useful for analyzing how structures of health care delivery tend to provide less than standard care to women who are older, have less income, or are less educated, black, or Hispanic. Data collection efforts which do not include structural and socioeconomic variables may result in an incomplete or misleading understanding of the determinants of underservice. These factors also need to be considered in the design and evaluation of public health policies and interventions meant to ameliorate the effects of underservice.

Screening mammography in community practice: positive predictive value of abnormal findings and yield of follow-up diagnostic procedures

OBJECTIVE

The purpose of this study was to gather from 50 community mammography practices that were included in the National Survey of Mammography Facilities data concerning abnormal findings on screening mammograms to determine the frequency of various recommendations made for patients who had abnormal findings and to compare these recommendations with the frequency with which the procedures were actually performed. We also determined the positive predictive value of screening mammograms (the number of cancers detected per 100 abnormal findings) and the yield (the number of cancers detected per 100 procedures done) of various diagnostic procedures done because of abnormal findings.

MATERIALS AND METHODS

We identified 1717 screening mammograms done in the last half of 1991 that had abnormal findings. Radiologic recommendations and follow-up procedures, including repeat standard (screening) mammography, additional mammographic views, sonography, clinical breast examination, needle aspiration, needle biopsy, and open biopsy, were identified for all of the cases from the radiologic records, and follow-up data were obtained from referring physicians. The positive predictive value and yield in the National Survey of Mammography Facilities were compared with data from the mammography screening practice of the University of California at San Francisco (UCSF), a facility noted for its clinical efficiency.

RESULTS

We estimate that 11% of all screening mammograms resulted in a recommendation for further diagnostic procedures. These 1717 mammograms with abnormal findings led to the following recommendations and procedures: repeat standard (screening) mammography, 610 (recommended)/635 (performed); additional mammographic views, 785/707; sonography, 400/345; biopsy, 189/229; and needle aspiration, 21/51. More procedures were done than were recommended in some cases because the results of certain procedures often led to the performance of other, additional procedures. The positive predictive value for screening examinations with abnormal findings was 3.5%, and the yield for open biopsy was 21%. In the UCSF data base, the positive predictive value for examinations with abnormal findings was 10%, and the yield for open biopsy was 34%.

CONCLUSION

The positive predictive value for examinations with abnormal findings and the yield for diagnostic procedures performed as a result of abnormal findings in 50 community radiologic facilities were higher than those reported in some earlier studies, a fact that raised concern about the induced cost of screening mammography. However, these values were low compared with those in the UCSF data base. This fact was particularly true of repeat standard (screening) mammography.

The costs of cancer care in the United States: implications for action

The total annual cost of cancer care in the United States (including direct and indirect costs) has been estimated at more than $96 billion. Although third-party payers have led the effort to reduce these costs, such high expenditures must concern society as a whole, since money spent on cancer care, whether through insurance premiums, taxes to support Medicare, or payouts from family savings, could be used for other purposes. In the future, attention may be shifted to more cost-effective strategies, including greater prevention efforts and development of better diagnostic tools to permit early detection. Improved diagnosis, however, presents an anomaly in that with earlier detection, survival is greater but the overall direct treatment costs are higher. This is why when making decisions about allocation of medical resources, the indirect costs of morbidity and mortality (which are reduced with early diagnosis) must be considered as well as the direct cost.

Imaging systems evaluation: effect of subtle cases on the design and analysis of receiver operating characteristic studies

OBJECTIVE

Large-scale receiver operating characteristic (ROC) studies are expensive and time-consuming. If most of the difference in diagnostic accuracy occurs in a subset of subtle cases, considerable effort could be saved by restricting comparisons to this subset. We investigate the effect of subtle cases on diagnostic accuracy, the magnitude of error that can occur because of an imbalance of subtle cases in two groups, and the potential for sample size reductions if only subtle cases are used.

METHODS

Data from a previous study of posteroanterior chest radiographs were reanalyzed separately for subsets of typical cases and subsets of subtle cases. Actually positive and actually negative cases were classified as subtle or typical and as difficult or easy for diagnosis of the specific abnormality. The area under the ROC curve (Az) was used as the measure of diagnostic accuracy. Pairwise comparisons were done among three techniques and for the detection of nodules and interstitial disease.

RESULTS

The performance index (Az) was significantly (> or = 25%) lower for the subset of subtle cases as compared with the subset of typical cases. The difference in observer performance between two techniques was more often greater in the subset of subtle cases than in the subset of typical cases.

CONCLUSION

The difference in diagnostic accuracy between the subset of typical cases and the subset of subtle cases is large enough that a difference in the proportion of subtle cases in two samples could result in clinically significant false differences in observer performance. Furthermore, the generally larger difference observed in the group of subtle cases suggests that sample sizes for some experiments could be reduced by 45-90% if the experiment were restricted to subtle cases.