- Email: [email protected]
A protocol for the investigation of infants and children with urinary tract infection
435
CLINICAL RADIOLOGY tract infection. Well over 5000 examinations were carried out in the last 5 year period. Regrettably by publishing this article, Clinical Radiology appears to have given credit to an outdated protocol and thus inadvertently has done disservice to modern paediatric practice. K. J. S H A H
Birmingham Children's Hospital Birmingham B16 8ET
References Steiner, G M (1988). Correspondence Clinical Radiology, 39, 690. Maling, T M J (1988). Correspondence Clinical Radiology, 39, 690. Whyte, K M , Abbott, GD, Kennedy, JC & Maling, T M J (1988). A protocol for investigation of infants and children with urinary tract infection. Clinical Radiology, 39, 278-280.
SIR T h a n k you for the opportunity to respond to Dr K. J. Shah's letter. The article reviews a protocol that was introduced in 1981 for children between the ages of 2 and 5 years. These children were spared the discomfort of having a V C U on presentation o f an initial UT1 because they had a normal IVU. The review, after five years of this protocol, showed that it did not miss children with significant V U R provided a VCU was performed on any children in this age group who continued to experience UTIs. We agree that the growth and improvement in ultrasound since 1981 has been such that it has an important role to play in the investigation of these children with UTI. We accept the role of ultrasound in the examination of the upper tract, but only in conjunction with a V C U in children under 5 years. Our view remains that all children under 2 years must have a V C U regardless of other imaging modalities for the upper urinary tract. In this age group, we accept either an IVU or ultrasound as a means for examining the upper tract and would agree that a strong argument can be made for ultrasound as it is the less invasive. In the 2-5 year age group, we believe that an initial V C U need not be performed unless an IVU demonstrates an upper tract abnormality. We have not been, and still remain to be, convinced that ultrasound examination alone can be relied upon to detect significant V U R in all instances. It is for this reason that we continue to use the IVU as the sole initial mode of investigation in this age group. We have no argument with the view that in children over 5 years of age a normal ultrasound examination suffices at the initial presentation. J. C. K E N N E D Y T. M. J. M A L I N G
Christchurch Hospital New Zealand
E V A L U A T I O N OF D I A G N O S T I C TESTS SIR - Dr Simpson's criticism (January 1989, p. 109) of six recent papers makes interesting reading. I am neither an involved editor, author, nor reviewer. Dr Simpson is of course on the side of the angels, looking down at those in limbo. I understand his irritation why can't people get this right? There are some difficulties, and I should like to select three. 1. Language. The words in this new bible are very poor. 'Specificity' and 'negative predictive value' is armchair nonsense. Unfortunately we seem stuck with it. No-one saying 'this is a highly specific test' ordinarily means "this test is terrific at picking out those who do not have the disease in question'. A n d the 'predictive value of a negative test result' has turned into a botched abbreviation. I know Esperanto was a very worthy effort all round, but no-one actually speaks a hopelessly stilted language, not since the Middle Ages. 2. Marble halls of truth stuff~ The entire framework discussed by Dr Simpson rests on the view that tests are experiments on a critical question: does the patient or does he not have the particular disease I have thought of?. This view of science (ideas first, observations second) is Karl Popper's, and radiologists have fastened on to it with delight (Sherwood, 1978). However, even an enthusiast has to admit that it is not always a realistic picture of radiology. Much testing is done without specific (ouch) questions, simply as data gathering on spec. Worse, 'gold standard' is far outside Popper's vocabulary. A good balance of uncertainties is the best we can achieve in science, and good pathologists do not pretend that they alone walk in marble halls. 3. Equivocal test results. Dr Simpson's own analysis of the six papers includes a plus/minus column always missing from the 2 x 2 tables he promotes. How does the new bible cope with this c o m m o n result, implicit in the ' b e s t guess' view of scientific method? Or with the
technically unsatisfactory result? The gospel-makers seem to say at present that these results m u s t be included in the sums. For instance in a cytology-and-breast-carcinoma study, that means counting the acellular aspirate (with which the cytologist can do nothing). Or: does a blank film obtained in a m a m m o g r a m study have to enter the specificity/ sensitivity stakes? The new bible looks extremely useful, but it talks funny, it is rigid and unrealistic in many ways, and there is quite a lot yet to be worked out. In searching for good papers, editors m u s t of course consider the statistics. I do not think they should be expected to check P values: that is too boring and condescending. For other reasons which I have tried to explain, editors might be better off if they stay nonconformist, and do not fuss endlessly over Bayes' hot gospel. T. S H E R W O O D
Department of Radiology University of Cambridge School of Clinical Medicine Addenbrooke's Hospital Hills Road, Cambridge CB2 2QQ
Reference Sherwood, T (1978). Science in radiology. Lancet, i, 594-595.
Sm I enjoyed reading Professor Sherwood's letter. He makes m a n y good points, very eloquently. Anyone interested in this subject should read the recent series of articles in the American Journal of Roentgenolog), on the quality of early M R research. These culminated in two articles in the issue of December, 1988 (Berk and Siegelman, Marglin and Moss). Before leaving the subject, and at the risk of getting increasingly out of m y depth, I cannot resist drawing attention to an article in the same copy of Clinical Radiology as m y previous letter. This is the inevitably contentious article by Skrabanek (1989), in which he once again is questioning the value of screening m a m m o g r a p h y . One of his points is the low positive predictive value (PPV) of screening mammography. He quotes one value of 8.6%. In arguing against him, an earlier article in the BMJ quotes values for the PPV of up to 60% (Reidy and Hoskins, 1988). It is clear that the figure of 8.6% refers to the PPV of a recall for assessment. The figure of 60% is probably the PPV o f a decision to refer a patient for biopsy after assessment. These writers appear to be confusing the two. I a m not wanting to take sides in the argument about the value of screening mammography. This example simply illustrates the confusion that m a y arise when the standard language of evaluation is used imprecisely. W. SIMPSON
Department of Diagnostic Radiology Newcastle General Hospital Westgate Road Newcastle Upon Tyne NE4 6BE
References Berk, R N & Siegelman, SS (1988). The value of early publications on efficacy of M R imaging. American Journal of Roentgenology, 151, 1240 1241. Marglin, SIE & Moss, A A (1988). Technology of assessment in radiology. American Journal of Roentgenology, 151, 1241 1242. Reidy, J & Hoskins, O (1988). Controversy over m a m m o g r a p h y screening. British Medical Journal, 297, 932 933. Skrabanek, P (1989). Shadows over screening m a m m o g r a p h y . Clinical Radiology, 40, 4-5.
O C C L U D E D C O R O N A R Y A R T E R I E S T R E A T E D BY PERCUTANEOUS CORONARY ANGIOPLASTY SIR An increasing number of patients with occluded coronary arteries are being treated by percutaneous coronary angioplasty. Although it is often possible to cross occluded coronary arteries with conventional guide wires and dilate these lesions with conventional balloons, there is a significant proportion of patients, especially those with longer occlusions, where conventional methods are unsuccessful. Various methods - -
CLINICAL RADIOLOGY tract infection. Well over 5000 examinations were carried out in the last 5 year period. Regrettably by publishing this article, Clinical Radiology appears to have given credit to an outdated protocol and thus inadvertently has done disservice to modern paediatric practice. K. J. S H A H
Birmingham Children's Hospital Birmingham B16 8ET
References Steiner, G M (1988). Correspondence Clinical Radiology, 39, 690. Maling, T M J (1988). Correspondence Clinical Radiology, 39, 690. Whyte, K M , Abbott, GD, Kennedy, JC & Maling, T M J (1988). A protocol for investigation of infants and children with urinary tract infection. Clinical Radiology, 39, 278-280.
SIR T h a n k you for the opportunity to respond to Dr K. J. Shah's letter. The article reviews a protocol that was introduced in 1981 for children between the ages of 2 and 5 years. These children were spared the discomfort of having a V C U on presentation o f an initial UT1 because they had a normal IVU. The review, after five years of this protocol, showed that it did not miss children with significant V U R provided a VCU was performed on any children in this age group who continued to experience UTIs. We agree that the growth and improvement in ultrasound since 1981 has been such that it has an important role to play in the investigation of these children with UTI. We accept the role of ultrasound in the examination of the upper tract, but only in conjunction with a V C U in children under 5 years. Our view remains that all children under 2 years must have a V C U regardless of other imaging modalities for the upper urinary tract. In this age group, we accept either an IVU or ultrasound as a means for examining the upper tract and would agree that a strong argument can be made for ultrasound as it is the less invasive. In the 2-5 year age group, we believe that an initial V C U need not be performed unless an IVU demonstrates an upper tract abnormality. We have not been, and still remain to be, convinced that ultrasound examination alone can be relied upon to detect significant V U R in all instances. It is for this reason that we continue to use the IVU as the sole initial mode of investigation in this age group. We have no argument with the view that in children over 5 years of age a normal ultrasound examination suffices at the initial presentation. J. C. K E N N E D Y T. M. J. M A L I N G
Christchurch Hospital New Zealand
E V A L U A T I O N OF D I A G N O S T I C TESTS SIR - Dr Simpson's criticism (January 1989, p. 109) of six recent papers makes interesting reading. I am neither an involved editor, author, nor reviewer. Dr Simpson is of course on the side of the angels, looking down at those in limbo. I understand his irritation why can't people get this right? There are some difficulties, and I should like to select three. 1. Language. The words in this new bible are very poor. 'Specificity' and 'negative predictive value' is armchair nonsense. Unfortunately we seem stuck with it. No-one saying 'this is a highly specific test' ordinarily means "this test is terrific at picking out those who do not have the disease in question'. A n d the 'predictive value of a negative test result' has turned into a botched abbreviation. I know Esperanto was a very worthy effort all round, but no-one actually speaks a hopelessly stilted language, not since the Middle Ages. 2. Marble halls of truth stuff~ The entire framework discussed by Dr Simpson rests on the view that tests are experiments on a critical question: does the patient or does he not have the particular disease I have thought of?. This view of science (ideas first, observations second) is Karl Popper's, and radiologists have fastened on to it with delight (Sherwood, 1978). However, even an enthusiast has to admit that it is not always a realistic picture of radiology. Much testing is done without specific (ouch) questions, simply as data gathering on spec. Worse, 'gold standard' is far outside Popper's vocabulary. A good balance of uncertainties is the best we can achieve in science, and good pathologists do not pretend that they alone walk in marble halls. 3. Equivocal test results. Dr Simpson's own analysis of the six papers includes a plus/minus column always missing from the 2 x 2 tables he promotes. How does the new bible cope with this c o m m o n result, implicit in the ' b e s t guess' view of scientific method? Or with the
technically unsatisfactory result? The gospel-makers seem to say at present that these results m u s t be included in the sums. For instance in a cytology-and-breast-carcinoma study, that means counting the acellular aspirate (with which the cytologist can do nothing). Or: does a blank film obtained in a m a m m o g r a m study have to enter the specificity/ sensitivity stakes? The new bible looks extremely useful, but it talks funny, it is rigid and unrealistic in many ways, and there is quite a lot yet to be worked out. In searching for good papers, editors m u s t of course consider the statistics. I do not think they should be expected to check P values: that is too boring and condescending. For other reasons which I have tried to explain, editors might be better off if they stay nonconformist, and do not fuss endlessly over Bayes' hot gospel. T. S H E R W O O D
Department of Radiology University of Cambridge School of Clinical Medicine Addenbrooke's Hospital Hills Road, Cambridge CB2 2QQ
Reference Sherwood, T (1978). Science in radiology. Lancet, i, 594-595.
Sm I enjoyed reading Professor Sherwood's letter. He makes m a n y good points, very eloquently. Anyone interested in this subject should read the recent series of articles in the American Journal of Roentgenolog), on the quality of early M R research. These culminated in two articles in the issue of December, 1988 (Berk and Siegelman, Marglin and Moss). Before leaving the subject, and at the risk of getting increasingly out of m y depth, I cannot resist drawing attention to an article in the same copy of Clinical Radiology as m y previous letter. This is the inevitably contentious article by Skrabanek (1989), in which he once again is questioning the value of screening m a m m o g r a p h y . One of his points is the low positive predictive value (PPV) of screening mammography. He quotes one value of 8.6%. In arguing against him, an earlier article in the BMJ quotes values for the PPV of up to 60% (Reidy and Hoskins, 1988). It is clear that the figure of 8.6% refers to the PPV of a recall for assessment. The figure of 60% is probably the PPV o f a decision to refer a patient for biopsy after assessment. These writers appear to be confusing the two. I a m not wanting to take sides in the argument about the value of screening mammography. This example simply illustrates the confusion that m a y arise when the standard language of evaluation is used imprecisely. W. SIMPSON
Department of Diagnostic Radiology Newcastle General Hospital Westgate Road Newcastle Upon Tyne NE4 6BE
References Berk, R N & Siegelman, SS (1988). The value of early publications on efficacy of M R imaging. American Journal of Roentgenology, 151, 1240 1241. Marglin, SIE & Moss, A A (1988). Technology of assessment in radiology. American Journal of Roentgenology, 151, 1241 1242. Reidy, J & Hoskins, O (1988). Controversy over m a m m o g r a p h y screening. British Medical Journal, 297, 932 933. Skrabanek, P (1989). Shadows over screening m a m m o g r a p h y . Clinical Radiology, 40, 4-5.
O C C L U D E D C O R O N A R Y A R T E R I E S T R E A T E D BY PERCUTANEOUS CORONARY ANGIOPLASTY SIR An increasing number of patients with occluded coronary arteries are being treated by percutaneous coronary angioplasty. Although it is often possible to cross occluded coronary arteries with conventional guide wires and dilate these lesions with conventional balloons, there is a significant proportion of patients, especially those with longer occlusions, where conventional methods are unsuccessful. Various methods - -