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In osteogenic sarcoma an increase in patient survival has been observed due to improvement of diagnostic and treatment methods. The objective of the investigation was to determine the usefulness of scintigraphy with 99mTc-MIBI in comparison to clinical revaluation, in order to assess tumor response (sarcoma) to chemotherapy previous to surgery. Patients with histopathological osteogenic sarcoma that received chemotherapy were included, clinical and scintigraphy response was assessed previous to the surgery. The gold standard for comparison was the degree necrosis histopathological analysis of the surgical specimen with measurement. Twelve patients met the inclusion criteria. A was observed a higher correlation between the 99mTc-MIBI and the histopathology. vs. clinical evaluation (0.89 vs. 0.59 respectively). Likewise the sensitivity (Se) and specificity (Sp) were superior (Se and Sp = 100% vs. Se 66.6% and Sp 75%) when therapeutically responses good and null were compared. We may conclude that scintigraphy with 99mTc-MIBI used to asses the response to presurgery chemotherapy in patients with osteogenic sarcoma, together with the clinical assessment, help the physician to make therapeutically decisions with more objectivity and certainly.

Objective: To identify some differences of patients and medical characteristics related to autopsy authorization., Design: Observational, cross-sectional study., Setting: Third-level medical care in a pediatric hospital., Methods: A specific mortality questionnaire was analyzed by members of the mortality staff, because they reviewed deaths which occurred between January 1994 and December 1995. Descriptive statistic and non-parametric tests (X2) were calculated to analyze data., Results: A total of 408 deaths were evaluated, in which 116 autopsies were done (28.4%). Children less than 18 months of age had the highest frequencies of autopsies (33.3%-30.7%). The patients referred by other units and the autopsy application done by a medical resident, had the highest frequencies of acceptance (32.5%, 35.3%, p < 0.05). The detection of diagnostic and therapeutic problems were related with high frequencies of autopsies (37.7%, 36% p < 0.05)., Conclusions: The results show us that some medical care factors are related to higher frequencies of autopsies. It is important to consider them in order to increase the capacity of teaching that a postmortem study has.

The objective was to identify the characteristics of epidemiologic designs enabling their classification. A critical review of the literature in the clinical epidemiologic area was done to establish the main differences between designs. A meeting with experts to discuss this controversial topic and obtain criteria by consensus was organized. We propose an integral classification based on levels with two fundamental shafts: intervention and explanatory reasoning.

The simple linear regression analysis, multiple linear regression and logistic regression constitute powerful statistical analysis tools widely used in clinical research. These kinds of analyses are based upon mathematical models which at the same time are established on certain basic assumptions. The regression analysis assumptions are basically: a) that the model is really linear, b) that the distribution of data is normal (from a statistical point of view), c) that the variances of the employed data are homogeneous (homocedastics) and that the included data are independent. The regression diagnostic has become popular as a form to evaluate if the assumptions have been accomplished, one of its most important techniques is the residual analysis. A residual can be defined as the value which measures the distance between the regression line and the corresponding value of the variable "y". Among these kinds of residuals used to evaluate the assumptions of regression are: the crude residual, the standardized, of student and the jackknife. The most useful among them is the jackknife residual. The usefulness and limitations of the residuals in the evaluation of the regression analysis assumptions are described, basically referring to the identification and handling of extreme values (outliers).

Introduction: Leukemia is the most frequent neoplasia in children; in our country it is the main cause of medical attention in children with cancer. The are different risk factors associated with the development of this kind of cancer., Objective: To identify which of the already known factors described in the literature associated with the development of leukemia are most frequent in the pediatric population of Mexico City., Material and Methods: A protective case-control study was carried out using prevalent and incident cases. In two third level hospitals of Mexico City, a total of 81 children who had been diagnosed as suffering from different kind of leukemia, confirmed by biopsy of bone marrow, were select and studied. The control were 154 children from two different sources: 77 of them came from the same hospital where the cases received medical care, the selection criteria was not to have any kind of neoplasia; and 77 came from the same community where those diagnosed children cases lived, the selection criteria for this group was that they were healthy children. Both cases and community controls were visited at home and interview to complete precoded questionnaire with the different variables of the study. The information from the hospital controls was obtained during the time they stayed in the hospital. Odds ratio (OR's) for the different associations were calculated, as well as its confidence intervals at 95% (IC) accord to Cornfield and unconditioned logistic regression was carried out to control confounding variables., Results: OR greater than 1 was found in those with familiar cancer background 1.93 (1.2-3.63); the mother being exposed to X-ray during pregnancy 1.89 (0.84-4.22); previous abortions before the child with leukemia was born 2.44 (1-06-5.68); being born from full term birth 2.42 (0.47-16.65); being born with weight greater that 3500 g 2.21 (1.04-4.33); being exposed to fertilizers 4.73 (1.04-24.14) and insecticides 1.93 (1.05-3.56). OR smaller than 1 was found in those who have been in a hospital because of an infectious disease during the first year of life 0.57 (0.17-1.74); to have suffered from chicken pox 0.59 (0.32-1.08). No association to parent's age or job was found. Multivariated analysis shows that the exposure to insecticide is the most important risk factor associated with the development of leukemia in children., Conclusions: We obtained positive associations to different risk factors described in the literature, having found that exposure to fertilizers is the most important risk factor and finding no association with the parent's occupation. This leads to the need of carrying out further studies to investigate, in more detail, the occupation of the father to confirm whether or not this is a risk factor.

Objectives: 1. To describe the frequency in which the thorax radiography is requested in a third-level pediatric hospital, 2. To identify the frequency of detected abnormalities in such a study by the radiology service, 3. To describe the frequency and the characteristics form the information considered as useful in a clinical way, not only in the radiography application but in the radiologic report and the clinical file as well, 4. To identify the frequency in which the thorax radiography result is associated with diagnosis changes and/or therapeutic ones. DESIGN OF THE INVESTIGATION: Descriptive survey., Study Units: 371 thorax X-rays completed during December 1990 and January 1991., Primary Results: The thorax radiographies were 32% of the entire radiological study during the survey; 335 of the latter ones (90%) were requested for inpatients. The hospital services which had the highest request for such a study were the Intensive Care Unit (n = 149, 40%) and Medical Pediatrics (n = 116, 31%). The most frequent diagnosis leading to the application was pneumonia (n = 55, 15%) and solid neoplasia (n = 51, 14%). Three-hundred forty eight of the applications had diagnostic impression given by the physician in charge(94%); whereas only 127 (34%) mentioned clinical data. The radiology report was attached to the file in 162 (44%) of the cases. It was found that form the patients who had a radiology report and the thorax radiography as an initial study (n = 95), 48 (50%) suffered from abnormalities. The results of the study were transcribed in the file in 58 cases (16%); the physician's interpretation was written down in 229 cases (62%) and in 84 studies (23%) there was no reference to the results of the study (P < 0.0001). Changes in the therapeutic plan of 93 cases (50%) were identified from the studies with official report by the radiologist, other radiology studies were requested in 65 of the patients (35%), after the interpretation of such study., Conclusions: Abnormalities in 50% were identified from the total thorax radiographies requested as the patient entered. The study application mentioned as a whole (94%) the diagnostic impression which led to the application, but only in 127 cases (34%) were supporting clinical data written down. The radiology report was attached to the file in less than half the cases (44%). In 63% of the cases the supporting reason of the study was written down whereas in 23% there was no reference to the result at all.

Introduction: There are different risk factors which have been related to the presence of leukemia in children. In the past years one of these factors has become relevant, the risk of living in an area near to high electric voltage lines, generators of electromagnetic fields of low frequency (EMF), which can cause development of leukemia in children., Objective: To learn whether living in an area close to EMF generator sources, electric transformers, high electric voltage distribution or transmission lines and electric substations, is a risk factor in the development of leukemia in children living in Mexico City., Material and Methods: A projective study of case-control was accomplished. The cases were obtained from hospitals of the third level. The diagnosis of leukemia in its different varieties was confirmed through biopsy of bone marrow. The controls were selected in the same hospital from inpatients and outpatients with different problems, except neoplasia. A total sample of 81 cases and 77 controls was analyzed. The residence of the controls and cases were visited using a questionnaire coded with the different study variables. To diminish the memory bias in relation to EMF, the subjects were shown different pictures pointing out the different sources of exposures, which were asked. Having obtained the information, different odds ratios (OR) were calculated for the different associations, as well as the confidence intervals at 95% and an unconditioned logistic regression was accomplished to know the adjusted OR., Results: There were no differences between the cases and controls according to the relative who gave the information, the current age of children, the parents's age, the social class and the parent's occupation. It was found that all the generating sources of EMF, which were involved in the study, had and OR above 1. Being the highest, the ones living near the distribution or transmission wires of high voltage with an OR of 2.63 (1.26-5.36) and 2.5 (0.97-6.67) respectively. When the distance of exposure was controlled, the highest OR was for distribution lines (OR 2.12; 0.79-5.85). When the analysis was applied to persons who have moved from the residence, it was found that the OR was above 1 in all the associations, the highest being the distribution wires and with the distance the highest was the electric substations. Furthermore, the multivariate analysis showed that the risk continued only for the distribution wires., Conclusions: The EMF exposure was found positive, however this is not very precise, that is why it is necessary to carry out other studies to confirm the existence of the association and correct possible biases which could appear during the research.

Objectives. 1) To identify the tests of immunological diagnosis with a high diagnostic efficiency in amebic liver abscess. 2) To determine the ideal cutoff point for such tests. 3) To identify the influence degree of the antigen used over the test efficiency. Design. Comparative survey. Study units. Analysis of 24 articles identified in the medical literature about tests of immunological diagnosis in amebic liver abscess. Measurements. Starting from the articles, operating characteristics curves (ROC) were established derived from the test application to patients with amebic liver abscess. Results. A great variability in the diagnostic efficiency was identified between the various tests, even when the analysis was focused on the investigations of a specific test. It was not possible to conclude which test had a major degree of efficiency due to such variability. The cutoff level considered as relevant was higher than the one traditionally used for indirect hemagglutination and it had concordance with the one presently accepted for the fluorescence antibodies test. By maintaining steady the spectrum of the study patients and the type of test, variability among the tests persisted. This was due to the use of different antigens. Conclusions. A great variation in the diagnostic efficiency of the analyzed tests was identified. The variation source was the type of test, the antigen used and probably the illness spectrum.

Objectives: 1. To determine the degree of correlation among different physicians concerning their initial diagnosis and 2. identify the degree of correlation between the probability that physicians assing an initial diagnosis and the number of days the patient is hospitalized, laboratory test and X-rays taken of the patient., Design: A comparative questionnaire., Study Site: Pediatric hospitalization Unit of a third level medical care ward of the Mexican Social Security Institute., Study Units: All new admissions or non-programmed readmitted patients to the hospital during the months of November and December 1990., Main Measurements: The treating physicians (Staff pediatricians (MB) and third (R3) and second (R2) year residents) were each asked to independently assign a probability (0 to 100) to each of the diagnosis emitted on the day the patient was admitted. When the patient was discharged, the number of days hospitalized as well as the number of laboratory tests and X-rays taken of the patient were added., Results: 106 patients were evaluated, a correlation was gathered between MBs and R3s of 0.79 (P less than 0.001) and among MBs and R2s of 0.83 (P less than 0.001). The correlation between resident physicians was discretely less 0.60 (P less than 0.01). When relating the probability assigned by the physicians and the number of days the patients were hospitalized, associations were observed of 0.31 (P less than 0.05), 0.15 (P less than 0.05) and 0.19 (P = 0.04) for the MB, R3 and R2s respectively. In the case of laboratory test a correlation of 0.38, 0.06 and 0.04 (MB, R3, R2 respectively) was found. None of these correlations were statistically significant. The X-rays showed a significant correlation in cases of the MBs (0.50, P less than 0.05)., Conclusions: The probabilities assigned by the staff physician as well as the resident doctors are closely related and a lesser grade of association is seen when comparing the residents among each other. No tendencies were identified in the correlation of the probability assigned by the residents and the variables analyzed. A consistent relation was seen between the staff physician and high probabilities, longer stays, and greater number of laboratory tests and X-rays.

In clinical pediatric research as in all research, one of the fundamental characteristics is the measurement of the studied features, either clinical, of laboratory or cabinet. A measurement must have two fundamental characteristics, for it to be considered as scientific: consistency and validity. The first one is centered on the variability of the measurement, which is due to the measuring instrument, to the subject or entity which is measured and to the individual or individuals who carry out the measuring, this is known as intra or interobserver variability, respectively. Validity is the fact of "actually" measuring what we want to measure. Both characteristics of measurement, are often mixed, between them and with other concepts, and this is the reason of not having a clear idea of what is the real meaning. This paper discusses the different terms that have been used for consistency and validity of a measurement. Also it points out how to assess consistency, from the validity, taking into account the measuring scale of the variables and the number of observers. Easy examples are used for the application of different formulas and for the interpretation of the results.