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Prediction of outcome of extremely premature babies
T H E LANCET
A statistical association between sleep quality and depression is hardly an exceptional observation. Nonetheless, here it highlights the obvious: that an individual's visual impairment has ramifications that extend beyond merely a quantitative description of their visual capacity, and into their mental and social wellbeing. We do not wish to disparage the contributions of those propounding chronobiological explanations of sleep disorders among the visually impaired. Indeed, doubtless some in our survey experienced sleep disturbance attributable to such causes. We believe, however, that alternative and valid explanations of the sleep problems of some blind individuals may exist. *Merrick J Moseley, Massoud Fouladi, Helen S Jones, Michael J Tobin 'Academic Unit of Ophthalmology, Imperial College School of Medicine at St Mary's. The Western Eye Hospital. London NW1 5YE. UK: Birmingham and Midland Eye Centre, Birmingham: and School of Education, University of Birmingham. Birmingham
1 Lockley S, Tabandeh H, Skene D, et al. Day-time naps and melatonin in blind people. Lancer 1995;346: 1491. 2 Leger D,Guilleminault C, Defrance R, Domont A, Paillard M. Blindness and sleep patterns. Lancer 1996; 348: 830-3 I. 3 Miles LE,Wilson MA. High incidence of cyclic sleepiwake disorders in the blind. Sleep Res 1977;6: 192. 4 Sasaki H,Nakata H, Murakami S , Uesugi R, Harada S, Teranishi M. Circadian sleep-walking rhythm disturbance in blind adolescence. Jap J l'sychiarr Neuml 1992;46: 209. 5 Tabandeh H,Lockley S , Skene D, Bird AC, Arendt J, Defrance R. Disturbances of sleep in blindness. Invesr Ophthalmol Visual Sci 1995; 36: S533.
Patent foramen ovale and decompression illness in divers SIR-we were interested in the description by Wilmshurst and colleagues (Sept 14, p 752)' of the use of button devices for closure of patent foramen ovale (PFO) in two divers; we entirely support their work in attempting t o prevent decompression illness in susceptible divers with PFO. The following case illustrates that neither identification of those who are susceptible nor the link between P F O and decompression illness are straightforward. A serving Royal Navy diver (now age 42 years) qualified for his profession in 1970. His duties mainly involve underwater explosive ordnance disposal, and from 1970 to 1984 he undertook many so-called provocative dives, including 75 m of seawater (msw) dives on air, 80 msw chamber dives, and dives involving surface decompression. In 1984, a cardiac murmur was detected o n routine medical examination. Echocardiography suggested an atrial septal defect, and cardiac catheterisation and oximetry showed an ostium secundum defect with a left to right shunt of 1.5/1. since then, he has continued to dive although restricted to 42 msw maximum depth and no repetitive dives. Over a professional career spanning 26 years he has never had any form of decompression illness. I n most cases of P F O with a significant shunt, bidirectional flow is probable at some stage during the cardiac cycle (I Simpson, personal communication). The potential for passage of venous bubble emboli to the arterial circulation presumably exists in all divers with such lesions. However, while a statistical link between P F O and decompression illness seems incontrovertible, it is also apparent that other, perhaps equally important, factors remain unidentified,2 and the best way to apply this knowledge is still unclear. In the two P F O cases described by Wilmshurst (both with a pronounced right to left component
Vol348 * November 30, 1996
to their shunt) invasive treatment to close the defect seems eminently reasonable. However, before applying this approach more widely the relation between PFO and the risk of decompression illness needs further investigation. We believe that the arguments for a prospective study of PFO in divers are stronger than ever: the forthcoming revision of The Diving at Work Regulations by the U K Health and Safety Commission may offer an opportunity to do this. *R
P Johnston, J R Broome, P
D Hunt, P J Benton
Institute of Naval Medicine, Gosport, Hampshire PO12 2DL. U K Wilmshurst P, Walsh K, Morrison L. Transcatheter occlusion of foramen ovale with a button device after neurological decompression illness in professional divers. Lancet 1996;348: 752-53. Byrne JC, Webb-Peploe MM. Relation between 2 Wilmshurst I", interatrial shunts, and decompression sickness in divers. Lancer 1989; ii: 1302-05. 1
SIR-The cases Wilmshurst' describes both had important shunts at rest. In the past he has proposed a patent foramen ovale as a cause of decompression illness in some patients. A patent foramen ovale may be present in up to 25% of people between the ages of 30 and 79 years. Obviously 25% of divers do not develop decompression illness. Standard teaching about patent foramen ovale is based on Thompson and Evan's results' which showed that most are only probe patent with a mean diameter of 0.1 cm. It is conceptually difficult to appreciate a substantial difficulty from so small and common a structure. More recently, however, a further study has shown that 58% of patent foramen ovale are greater than 5 m m diameter.' The size and presence of interatrial shunting are likely to be important factors in which patent foramen ovale contribute to decompression illnesses. Perhaps the knowledge that so many are greater than 5 mm will help to allay the scepticism that has surrounded this subject. Some of this scepticism may be exacerbated by different interpretations of the terminology. Since the proposed pathogenesis of decompression illness in the presence of patent foramen ovale is right to left shunting it is this term which should in future be used. There may be some difficulty in differentiating between a large patent foramen ovale and a small atrial septal defect but both would display the pathogenetically and diagnostically significant interatrial shunting. Mark Turner Department of Cardiology. Derriford Hospital. Plymouth PL6 8DH. UK
1 Wilmshurst P, Walsh K, Morrison L. Transcatheter occlusion of foramen ovale with a button device after neurological decompression illness in professional divers. Lancet 1996;348: 752. 2 Thompson T,Evans W. Paradoxical embolism. Q J M e d 1930; 23: 135-50. 3 Hagen PT, Scholtz DG, Edwards WD. Incidence and size of patent foramen ovale during the first 10 decades of life: an autopsy study of 965 normal hearts. Mayo Clin Proc 1984;59: 17-20,
Prediction of outcome of extremely premature babies SIR--WhilSt I am delighted that Koh (Oct 5, p 963)' finds my recent systematic review of outcome in very preterm infants useful, I am concerned that he has applied a very broad brush to it in order to produce his ready reckoner. As I pointed out, there is still a lack of good quality follow-up information. This means that the confidence intervals for prediction of handicap are very wide. It does not follow that because between 48% and 57% of the 25-week gestation survivors were normal the rest were handicapped, as Koh
1515
T H E LANCET
states. Indeed, among those who were assessed major handicap was found in only 38% (95% C I 30-47%). T h e 14% gap between these estimations is made up by infants with minor handicap, and exists in part because of the inaccuracy generated by trying to combine results from disparate pieces of research. Although I am entirely supportive of prospective parents of very premature infants having access to good quality, up-to-date information about the outcome of neonatal intensive care (which is why I wrote the review) this information needs to be as accurate as possible. Koh's oversimplification is too imprecise to be recommended for this purpose. Janet M Rennie Children Nationwide Neonatal Intensive Care Unit. King's College Hospital, Denmark Hill, London SE5 9RS. U K 1 Koh THHG. Simplified way of counselling parents about outcome of extremely premature babies. Lancet 1996; 348: 963.
these patients with no receptive non-verbal communication (ie, no apparent understanding of the gestures or facial expressions of others) implies that most were at a very profound level of retardation. This interpretation is confirmed by a 1994 analysis of the identical data-set.' In this, the median survival of children in persistent vegetative state was 2.6 years in those under 1 year of age, and 5.7 years in those aged 1.0 to 15.9 years. Thus the median survival of children in subgroups 1-3 of the 1993 Eyman study was actually the same, or worse, than that of children in a vegetative state. This study is therefore not an appropriate basis for estimating life expectancy in children who are at a higher level than persistent vegetative state. T W Anderson Department of Health Care and Epidemiology. University of British Columbia. Vancouver. Canada V6T 123
1 2
Life expectancy in cerebral palsy SIR-UK and Canadian studies of children with cerebral palsy have suggested that life expectancy may be better than is generally realised.' ' This has important implications for public-health planning, medicolegal settlements, and-not least-the children and their families. However, a study by Eyman et al' in California involving children with somewhat similar handicaps has yielded more pessimistic estimates of survival and-partly because of the much larger size of this study-these results have tended to be viewed as the most reliable. Predicted life expectancy can vary widely depending on which study is used. T h u s a severely disabled child may be estimated to have a life expectancy of less than 5' or over 30 years.' ' The purpose of this letter is to draw attention to an aspect of the 1993 Eyman study that appears to have been overlooked. In this study, survival data was provided for six subgroups of patients with various combinations of physical disabilities, and a summary of these data is shown in the table for subgroups 1-3. It is clearly impossible to estimate an average level of mental retardation within each of these subgroups, since a large proportion of each group has only a suspected level of mental retardation, which could mean either severe or profound. However, the high percentage of
3 4
5
Evans PM, Evans S J W , Alberman E. Cerebral palsy: why we must plan for survival. Arch Dir Child 1990; 65: 1329-33. Hutton JL, Cooke T, Pharoah POD. Life expectancy in children with cerebral palsy. BMJ 1994; 309: 431-35. MacKinnon M, White CP. The life expectancy of Crichton JU, persons with cerebral palsy. Dev Med Child Neurol 1995; 37: 567-76. Eyman RK, Grossman HJ, Chaney FW,Call TL. Survival of profoundly disabled people with severe mental retardation. A m J D i s Child 1993; 147: 329-36. Ashwal S, Eyman RK, Call T L . Life expectancy of children in a persistent vegetative state. Pediarr Neurol 1994; 10: 27-33.
Antenatal screening of thyroid antibodies
SIR-we agree with Ball (Oct 5, p 906)' that the case for antenatal thyroid antibody screening remains to be made, preferably by cost-benefit analysis, as we have suggested.' We did not intend to suggest that screening is mandatory but, rather, to emphasise that symptoms and signs of postpartum hyperthyroidism and hypothyroidism may occur even when the thyroid appears to be functioning normally, and also in thyroid antibody-positive women who were euthyroid. We were not assessing postpartum symptomatology by way of comparison with antenatal or gestation related symptoms. Despite 35% of the thyroid peroxidase antibody-positive ( T P O Ab-positive) group not being examined (their demographic features being the same as the patients studied) the size of our group (152 Ab-positive and 230 controls, matched for age, parity, and demographics) suggests Available for 1993 subgroups 1994 minimum effect of any bias. Most women who declined to followup persistent 2 take part in the study gave domestic and social reasons. (1993and vegetative 94) state Although it would have been useful to compare variation between individuals and to use serial testing it is nevertheless Number 128 248 985 382 1376 847 Some arm/hand use (99.9%+) + unlikely that the high prevalence of differences between the Feeding (2.0%T) T FBO (64%T) would be explained by chance. -T - groups ~ Median survival ( yr) Ball is correct in stating that T P O Ab is a weak predictor Age 4 0.9 1.4 1.2 2.6 (50%) of postpartum thyroid dysfunction; however, 30% of Age 1-15.9 4.8 5.3 5.7 5.71 ~ ~ _ _ all T_ P O Ab-positive patients (half with and half without Mental retardation (96) postpartum thyroid disease) will develop depressive Mild or moderate 57.3 0 0 0 symptoms. Furthermore, we have shown that three Severe 12.8 6.4 9.2 10.0 evaluations-TPO Ab-dependent complement activation at Profound 11.9 636 35.9 46.4 Suspected 18.0 30.0 54.9 43.6 6 weeks postpartum,' serum thyroglobulin,' and thyroid ~ ~ morphology by ultrasound'-will increase the specificity of Receptive non-verbal communication (%) postpartum thyroid disease diagnosis to around 75%. We None 20.5 96.8 88.5 91.1 100 wish to add that while, in our experience, many patients with Some 79.4 3.2 11.5 8.9 0 postpartum hypothyroidism can be successfully treated with *Weighted average of median suwival in age groups 1-1.9 years (4.2 years), thyroxine to alleviate their symptoms, in postpartum T P O 2.0-5.9 years (5 2). and 7.0-18.9 years (9.9). From Eyrnan et al' and Ashwal et Ab-positive women intervention with T, does not seem to al.'All patients in subgroups 1-3 were immobile, could not roll, were incontinent, and were fed by others (FBO) or by tube ( T ) . alleviate depressive symptoms. As indicate in our report,' we believe that sufficient data Table: Data for subgroups 1-3 in cerebral
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~
1516
-
Vol 348 November 30, 1996
A statistical association between sleep quality and depression is hardly an exceptional observation. Nonetheless, here it highlights the obvious: that an individual's visual impairment has ramifications that extend beyond merely a quantitative description of their visual capacity, and into their mental and social wellbeing. We do not wish to disparage the contributions of those propounding chronobiological explanations of sleep disorders among the visually impaired. Indeed, doubtless some in our survey experienced sleep disturbance attributable to such causes. We believe, however, that alternative and valid explanations of the sleep problems of some blind individuals may exist. *Merrick J Moseley, Massoud Fouladi, Helen S Jones, Michael J Tobin 'Academic Unit of Ophthalmology, Imperial College School of Medicine at St Mary's. The Western Eye Hospital. London NW1 5YE. UK: Birmingham and Midland Eye Centre, Birmingham: and School of Education, University of Birmingham. Birmingham
1 Lockley S, Tabandeh H, Skene D, et al. Day-time naps and melatonin in blind people. Lancer 1995;346: 1491. 2 Leger D,Guilleminault C, Defrance R, Domont A, Paillard M. Blindness and sleep patterns. Lancer 1996; 348: 830-3 I. 3 Miles LE,Wilson MA. High incidence of cyclic sleepiwake disorders in the blind. Sleep Res 1977;6: 192. 4 Sasaki H,Nakata H, Murakami S , Uesugi R, Harada S, Teranishi M. Circadian sleep-walking rhythm disturbance in blind adolescence. Jap J l'sychiarr Neuml 1992;46: 209. 5 Tabandeh H,Lockley S , Skene D, Bird AC, Arendt J, Defrance R. Disturbances of sleep in blindness. Invesr Ophthalmol Visual Sci 1995; 36: S533.
Patent foramen ovale and decompression illness in divers SIR-we were interested in the description by Wilmshurst and colleagues (Sept 14, p 752)' of the use of button devices for closure of patent foramen ovale (PFO) in two divers; we entirely support their work in attempting t o prevent decompression illness in susceptible divers with PFO. The following case illustrates that neither identification of those who are susceptible nor the link between P F O and decompression illness are straightforward. A serving Royal Navy diver (now age 42 years) qualified for his profession in 1970. His duties mainly involve underwater explosive ordnance disposal, and from 1970 to 1984 he undertook many so-called provocative dives, including 75 m of seawater (msw) dives on air, 80 msw chamber dives, and dives involving surface decompression. In 1984, a cardiac murmur was detected o n routine medical examination. Echocardiography suggested an atrial septal defect, and cardiac catheterisation and oximetry showed an ostium secundum defect with a left to right shunt of 1.5/1. since then, he has continued to dive although restricted to 42 msw maximum depth and no repetitive dives. Over a professional career spanning 26 years he has never had any form of decompression illness. I n most cases of P F O with a significant shunt, bidirectional flow is probable at some stage during the cardiac cycle (I Simpson, personal communication). The potential for passage of venous bubble emboli to the arterial circulation presumably exists in all divers with such lesions. However, while a statistical link between P F O and decompression illness seems incontrovertible, it is also apparent that other, perhaps equally important, factors remain unidentified,2 and the best way to apply this knowledge is still unclear. In the two P F O cases described by Wilmshurst (both with a pronounced right to left component
Vol348 * November 30, 1996
to their shunt) invasive treatment to close the defect seems eminently reasonable. However, before applying this approach more widely the relation between PFO and the risk of decompression illness needs further investigation. We believe that the arguments for a prospective study of PFO in divers are stronger than ever: the forthcoming revision of The Diving at Work Regulations by the U K Health and Safety Commission may offer an opportunity to do this. *R
P Johnston, J R Broome, P
D Hunt, P J Benton
Institute of Naval Medicine, Gosport, Hampshire PO12 2DL. U K Wilmshurst P, Walsh K, Morrison L. Transcatheter occlusion of foramen ovale with a button device after neurological decompression illness in professional divers. Lancet 1996;348: 752-53. Byrne JC, Webb-Peploe MM. Relation between 2 Wilmshurst I", interatrial shunts, and decompression sickness in divers. Lancer 1989; ii: 1302-05. 1
SIR-The cases Wilmshurst' describes both had important shunts at rest. In the past he has proposed a patent foramen ovale as a cause of decompression illness in some patients. A patent foramen ovale may be present in up to 25% of people between the ages of 30 and 79 years. Obviously 25% of divers do not develop decompression illness. Standard teaching about patent foramen ovale is based on Thompson and Evan's results' which showed that most are only probe patent with a mean diameter of 0.1 cm. It is conceptually difficult to appreciate a substantial difficulty from so small and common a structure. More recently, however, a further study has shown that 58% of patent foramen ovale are greater than 5 m m diameter.' The size and presence of interatrial shunting are likely to be important factors in which patent foramen ovale contribute to decompression illnesses. Perhaps the knowledge that so many are greater than 5 mm will help to allay the scepticism that has surrounded this subject. Some of this scepticism may be exacerbated by different interpretations of the terminology. Since the proposed pathogenesis of decompression illness in the presence of patent foramen ovale is right to left shunting it is this term which should in future be used. There may be some difficulty in differentiating between a large patent foramen ovale and a small atrial septal defect but both would display the pathogenetically and diagnostically significant interatrial shunting. Mark Turner Department of Cardiology. Derriford Hospital. Plymouth PL6 8DH. UK
1 Wilmshurst P, Walsh K, Morrison L. Transcatheter occlusion of foramen ovale with a button device after neurological decompression illness in professional divers. Lancet 1996;348: 752. 2 Thompson T,Evans W. Paradoxical embolism. Q J M e d 1930; 23: 135-50. 3 Hagen PT, Scholtz DG, Edwards WD. Incidence and size of patent foramen ovale during the first 10 decades of life: an autopsy study of 965 normal hearts. Mayo Clin Proc 1984;59: 17-20,
Prediction of outcome of extremely premature babies SIR--WhilSt I am delighted that Koh (Oct 5, p 963)' finds my recent systematic review of outcome in very preterm infants useful, I am concerned that he has applied a very broad brush to it in order to produce his ready reckoner. As I pointed out, there is still a lack of good quality follow-up information. This means that the confidence intervals for prediction of handicap are very wide. It does not follow that because between 48% and 57% of the 25-week gestation survivors were normal the rest were handicapped, as Koh
1515
T H E LANCET
states. Indeed, among those who were assessed major handicap was found in only 38% (95% C I 30-47%). T h e 14% gap between these estimations is made up by infants with minor handicap, and exists in part because of the inaccuracy generated by trying to combine results from disparate pieces of research. Although I am entirely supportive of prospective parents of very premature infants having access to good quality, up-to-date information about the outcome of neonatal intensive care (which is why I wrote the review) this information needs to be as accurate as possible. Koh's oversimplification is too imprecise to be recommended for this purpose. Janet M Rennie Children Nationwide Neonatal Intensive Care Unit. King's College Hospital, Denmark Hill, London SE5 9RS. U K 1 Koh THHG. Simplified way of counselling parents about outcome of extremely premature babies. Lancet 1996; 348: 963.
these patients with no receptive non-verbal communication (ie, no apparent understanding of the gestures or facial expressions of others) implies that most were at a very profound level of retardation. This interpretation is confirmed by a 1994 analysis of the identical data-set.' In this, the median survival of children in persistent vegetative state was 2.6 years in those under 1 year of age, and 5.7 years in those aged 1.0 to 15.9 years. Thus the median survival of children in subgroups 1-3 of the 1993 Eyman study was actually the same, or worse, than that of children in a vegetative state. This study is therefore not an appropriate basis for estimating life expectancy in children who are at a higher level than persistent vegetative state. T W Anderson Department of Health Care and Epidemiology. University of British Columbia. Vancouver. Canada V6T 123
1 2
Life expectancy in cerebral palsy SIR-UK and Canadian studies of children with cerebral palsy have suggested that life expectancy may be better than is generally realised.' ' This has important implications for public-health planning, medicolegal settlements, and-not least-the children and their families. However, a study by Eyman et al' in California involving children with somewhat similar handicaps has yielded more pessimistic estimates of survival and-partly because of the much larger size of this study-these results have tended to be viewed as the most reliable. Predicted life expectancy can vary widely depending on which study is used. T h u s a severely disabled child may be estimated to have a life expectancy of less than 5' or over 30 years.' ' The purpose of this letter is to draw attention to an aspect of the 1993 Eyman study that appears to have been overlooked. In this study, survival data was provided for six subgroups of patients with various combinations of physical disabilities, and a summary of these data is shown in the table for subgroups 1-3. It is clearly impossible to estimate an average level of mental retardation within each of these subgroups, since a large proportion of each group has only a suspected level of mental retardation, which could mean either severe or profound. However, the high percentage of
3 4
5
Evans PM, Evans S J W , Alberman E. Cerebral palsy: why we must plan for survival. Arch Dir Child 1990; 65: 1329-33. Hutton JL, Cooke T, Pharoah POD. Life expectancy in children with cerebral palsy. BMJ 1994; 309: 431-35. MacKinnon M, White CP. The life expectancy of Crichton JU, persons with cerebral palsy. Dev Med Child Neurol 1995; 37: 567-76. Eyman RK, Grossman HJ, Chaney FW,Call TL. Survival of profoundly disabled people with severe mental retardation. A m J D i s Child 1993; 147: 329-36. Ashwal S, Eyman RK, Call T L . Life expectancy of children in a persistent vegetative state. Pediarr Neurol 1994; 10: 27-33.
Antenatal screening of thyroid antibodies
SIR-we agree with Ball (Oct 5, p 906)' that the case for antenatal thyroid antibody screening remains to be made, preferably by cost-benefit analysis, as we have suggested.' We did not intend to suggest that screening is mandatory but, rather, to emphasise that symptoms and signs of postpartum hyperthyroidism and hypothyroidism may occur even when the thyroid appears to be functioning normally, and also in thyroid antibody-positive women who were euthyroid. We were not assessing postpartum symptomatology by way of comparison with antenatal or gestation related symptoms. Despite 35% of the thyroid peroxidase antibody-positive ( T P O Ab-positive) group not being examined (their demographic features being the same as the patients studied) the size of our group (152 Ab-positive and 230 controls, matched for age, parity, and demographics) suggests Available for 1993 subgroups 1994 minimum effect of any bias. Most women who declined to followup persistent 2 take part in the study gave domestic and social reasons. (1993and vegetative 94) state Although it would have been useful to compare variation between individuals and to use serial testing it is nevertheless Number 128 248 985 382 1376 847 Some arm/hand use (99.9%+) + unlikely that the high prevalence of differences between the Feeding (2.0%T) T FBO (64%T) would be explained by chance. -T - groups ~ Median survival ( yr) Ball is correct in stating that T P O Ab is a weak predictor Age 4 0.9 1.4 1.2 2.6 (50%) of postpartum thyroid dysfunction; however, 30% of Age 1-15.9 4.8 5.3 5.7 5.71 ~ ~ _ _ all T_ P O Ab-positive patients (half with and half without Mental retardation (96) postpartum thyroid disease) will develop depressive Mild or moderate 57.3 0 0 0 symptoms. Furthermore, we have shown that three Severe 12.8 6.4 9.2 10.0 evaluations-TPO Ab-dependent complement activation at Profound 11.9 636 35.9 46.4 Suspected 18.0 30.0 54.9 43.6 6 weeks postpartum,' serum thyroglobulin,' and thyroid ~ ~ morphology by ultrasound'-will increase the specificity of Receptive non-verbal communication (%) postpartum thyroid disease diagnosis to around 75%. We None 20.5 96.8 88.5 91.1 100 wish to add that while, in our experience, many patients with Some 79.4 3.2 11.5 8.9 0 postpartum hypothyroidism can be successfully treated with *Weighted average of median suwival in age groups 1-1.9 years (4.2 years), thyroxine to alleviate their symptoms, in postpartum T P O 2.0-5.9 years (5 2). and 7.0-18.9 years (9.9). From Eyrnan et al' and Ashwal et Ab-positive women intervention with T, does not seem to al.'All patients in subgroups 1-3 were immobile, could not roll, were incontinent, and were fed by others (FBO) or by tube ( T ) . alleviate depressive symptoms. As indicate in our report,' we believe that sufficient data Table: Data for subgroups 1-3 in cerebral
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1516
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Vol 348 November 30, 1996