ATLANTOAXIAL INSTABILITY, SPORT, AND DOWN SYNDROME

438 GAS

BUBBLES, AND DIVING SiR,—Dr Polkinghome and his colleagues (Dec 17, p 1381) report alterations in capillary density and other retinal changes in RETINAL

CHANGES,

divers which are consistent with obstruction of retinal and choroidal circulations. They speculate that these changes could be due to intravascular bubble formation during decompression. Despite these ocular abnormalities no diver had visual impairment. Acute visual impairment does occur after decompression from shallow and short dives, which should produce only a small increase in tissue nitrogen. For dives to 25-50 m in sea water I have observed visual impairment in wearers of non-permeable contact lenses, even when the dive was within the "no-stop" time (the longest permissible dive time not requiring staged decompression stops). The mechanism is that bubbles of gas (presumably nitrogen) are liberated from supersaturated tears during decompression. The gas cannot diffuse away from the site of release between the contact lens and the cornea, and the bubbles increase during the ascent, following Boyle’s law. The photograph shows the typical findings in a recreational diver after a single shallow air dive not requiring staged decompression. The bubbles produce multiple indentations in the cornea and corneal oedema, causing severe blurring of vision; and the reduced visual acuity and corneal changes generally take 1-2 h to disappear. The long-term consequences of repeated corneal damage in divers wearing hard contact lenses are unclear but the problem can be prevented by use of gas-permeable lenses or a mask fitted with prescription lenses.

have revealed acute retinal changes of microvascular obstruction, which we have attributed in partto gaseous microembolism. The changes were usually reversed one week postoperatively and we did not see the more chronic features described by Polkinghome et al. We also obtained histological evidence of focal ischaemia in the nerve fibre layer of the retina and intravascular platelet-fibrin microaggregates.1 When addressing the question of whether retinal fluorescein angiography can predict focal ischaemia elsewhere in the central nervous system, it would be of interest to look at neurological, neuropsychological, and retinal data in the same group of divers to see if the indices of retinal infarction described by Polkinghome et al are related to cerebral dysfunction. The finding of a positive association might contribute as much to safer cardiopulmonary bypass as to safer diving. C. BLAUTH Department of Surgery, P. SMITH Medical School, Royal Postgraduate London W12 0HS K. M. TAYLOR 1 Aarli

JA, Vaernes R, Brubakk AO, et al. Central nervous dysfunction associated with deep sea diving. Acta Neurol Scand 1985, 71: 2-10. 2 Smith PLC, Treasure T, Newman S, et al. Cerebral consequences of cardiopulmonary bypass. Lancet 1986; i :823-25. 3. Blauth C, Arnold J, Kohner EM, Taylor KM. Retinal microembolism during cardiopulmonary bypass demonstrated by fluorescein angiography Lancet 1986,ii 837-39 4. Blauth C, Arnold J, Schulenberg WE, McCartney A, Taylor KM Cerebral microembolism during cardiopulmonary bypass J Thorac Cardiovasc Surg 1988, 95: 668-76

ATLANTOAXIAL

INSTABILITY, SPORT, AND DOWN SYNDROME

PETER WILMSHURST, Medical Adviser, British Sub-Aqua Club

SiR,—Your Jan 7 editorial notes that neurological damage due to atlantoaxial instability in individuals with Down syndrome is infrequent. Nevertheless, Davidson’s is an underestimate.’ Davidson found only 37 published instances yet our literature search has uncovered at least 60 people with Down syndrome and symptomatic atlantoaxial instability. In 1984 we mentioned 42 cases of Down syndrome with significant neurological symptoms,2 and many other case-reports have appeared since then. Physicians caring for patients with Down syndrome indicated that many more such cases have not been published. Our study on 404 people with Down syndrome revealed that 1 5% of an unselected series had symptomatic atlantoaxial instability.3 Your editorialist suggests that a concurrent upper respiratory infection causes retropharyngeal ligamentous laxity but I doubt if upper-respiratory-tract infections per se result in atlantoaxial instability. Since infections are very common in children with Down syndrome or without this chromosome disorder so one would expect atlantoaxial instability to be much more common if respiratory infections cause the instability. Moreover, there is no evidence that infections of the upper respiratory tract lead to isolated ligamentous laxity between atlas and odontoid process. Probably more important in the pathogenesis is the increased prevalence of upper cervical spine abnormalities in children with Down syndrome and atlantoaxial instability. Cervical spine anomalies, besides ligamentous laxity, may contribute to atlantoaxial instability. Although the prevalence of symptomatic atlantoaxial dislocation resulting from sports injury is not known exactly we have found a history of preceding injury in at least 17% of cases.2 An injury to the cervical spine might either cause atlantoaxial dislocation or be a contributing factor, augmenting pre-existing symptoms. You ask "should we deprive 18% of Down individuals from participating in

SiR,—Reading Dr Polkinghome and colleagues’ paper we noted similarity between decompression after diving and cardiopulmonary bypass for cardiac surgery. Together, these are probably the commonest situations in which intravascular gas bubble formation and embolism occur in man. Although the circumstances are very different, neurological and neuropsychological dysfunction have also been noted in divers and in patients after cardiac surgery. 12 Our studies of the optic fundus in patients on cardiopulmonary bypass with a bubble oxygenator3’

diving, butterfly swimming, gymnastics, high jump, pentathlon, soccer, rugby, and somersaulting with all the benefits these can bring?" We may not know the exact risks involved in such activities but advising against the above activities in individuals with Down syndrome who had asymptomatic atlantoaxial instability seems a sensible precaution. That does not mean that these children should be excluded from other recreational and sporting activities, and they should be encouraged to participate in those Special Olympics activities which do not carry the risk of cervical spine injury. With radiographs of the upper cervical spine more than 85% of children with Down syndrome will be found not to have atlantoaxial

Bubbles behind

contact

lens of diver.

The clinical significance of these observations is greater than the ocular findings. These observations prove that after many shallow dives shorter than the maximum no-stop time, bubbles form in tissue despite correct decompression procedures. This suggests that after many dives with a low theoretical risk of decompression sickness, bubble formation in vivo is occurring. Diving is a new sport. The long-term consequences of repeated asymptomatic decompression and in-vivo bubble liberation are not known. Department of Cardiology, St Thomas’ Hospital, London SE1 7EH

a

remarkable

439

instability; they can take part in all physical education programmes and spOrts3 and their parents can be reassured. With the other 13% or so who have instability but no symptoms, special precautions can be taken with regular check-ups to identify children at high risk before spinal cord damage ensues. The 1-2% of individuals with Down syndrome and symptoms of atlantoaxial instability will usually require surgical stabilisation of the upper cervical spine. Department of Pediatncs, Brown University Program in Medicine and Child Development Center, Rhode Island Hospital,

S. M. PUESCHEL

Providence, Rhode Island 02903, USA

1 Davidson RG. Atlantoaxial instability in individuals with Down syndrome: a fresh look at the evidence. Pediatrics 1988; 81: 857-65. 2 Pueschel SM, Herndon JH, Gelch MM, et al. Symptomatic atlantoaxial subluxation in persons with Down syndrome. J Pediatr Orthop 1984; 4: 682-88. 3. Pueschel SM, Scola FH Atlantoaxial instability in individuals with Down syndrome:

epidemiologic, radiographic, and clinical studies. Pediatrics 1987, 80:

550-60.

HYPONATRAEMIA AND HAEMOLYTIC URAEMIC SYNDROME

SiR,—Hyponatraemia is a common feature of the haemolytic uraemic syndrome (HUS), 1.2 reflecting enteric electrolyte losses and renal impairment. In a national survey the British Association for Paediatric Nephrology, the British Paediatric Surveillance Unit, and the division of enteric pathogens, Central Public Health Laboratory, collected clinical and laboratory data on HUS from admission and for the duration of the illness. Of the 290 children notified 220 (76%) had a plasma sodium below 130 mmot/1 during the acute illness, the lowest recorded plasma sodium being on the day of admission in 67 (23%). 55 patients had seizures. Although seizures in children with HUS are multifactorial, hyponatraemia was recorded in 84% of those with seizures but in only 50% of those without seizures (p < 0 001) and convulsions occurred within 24 h of the lowest sodium in 35 of the 55 children. In individual cases the state of hydration, as assessed by the admitting paediatrician, did not correlate with hyponatraemia (figure). No difference was found between the three groups of children (overloaded, normal, dehydrated) in the duration or severity of prodrome or the incidence of vomiting, and prodromal features could not be used to identify hyponatraemic cases. Worryingly, 84 (29%) of the children with HUS reached the nadir

of their hyponatraemia 4 or more days after admission. This have been due to an incorrect assessment of hydration at presentation, and/or inappropriate fluid and electrolyte

must

prescription. There are no physical signs to warn physicians of hyponatraemia, and we recommend that any child presenting with bloody diarrhoea (the typical prodrome of HUS) should have close monitoring of plasma sodium from presentation. Moreover, since sodium and water requirements in these children with renal impairment are often complicated by continued losses through vomiting or diarrhoea, sodium and water requirements must be estimated

independently. Department of Nephrology, Children’s Hospital, Birmingham B16 SET 1.

DAVID MILFORD C. M. TAYLOR

Barwick K, Fishaut M, Kashgarian M, Siegel J. The importance of nonrenal involvement in hemolytic uremic syndrome Pediatrics 1980; 65: 115-20. 2. Taylor CM, White RHR, Winterborn MH, Rowe B Haemolytic-uraemic syndrome clinical experience of an outbreak in the West Midlands Br Med J 1986, 292: 1513-16

Upadhyaya K,

PROGUANIL

SiR,—Dr Hanson and colleagues (Jan 28, p 225) do not qualify their claim to report two novel side-effects of proguanil. Hair loss coincided with taking proguanil in 10 out of about 1750 Scandinavians in Tanzania; it was reversed in all 10 cases when proguanil was stopped and recurred in 2 on rechallenge. The scaling of palms and soles was a less frequent and less distressing complaint. I have prescribed proguanil for several thousands of patients of both sexes in Nigeria and Zambia, both long term (eg, to about 5000 patients with sickle-cell disease and to patients with the hyperreactive malarial splenomegaly syndrome, lymphomas, or leukaemias) and short term to pregnant women and patients receiving blood transfusions or total dose iron infusions. I do not recollect a single African patient complaining of loss of hair or scaling of the skin. A racial susceptibility in northern Europeans might be postulated; however, although there have been anecdotal reports of mouth ulcers and loss of memory blamed on proguanil, I never heard, in 22 years, of complaints of hair loss or scaling of the skin amongst the European expatriate communities, many of whom were taking proguanil, often for years. That all those who lost their hair were women, except for 1 girl, does suggest that other factors were involved, which could include some related to hairdressing, for example. Hanson and his colleagues should look for other factors common to these women and related causally to their loss of hair, either alone or in conjunction with co-factors, which might include proguanil. Proguanil is the safest and most effective single antimalarial prophylactic for use in tropical Africa. It could be disastrous if anyone in need of protection against malaria were persuaded to discontinue prophylaxis or to change to some less effective regimen out of an unsubstantiated fear of loss of hair. Flat E33, Du Cane Court, Balham High Road, London SW17 7JJ

ALAN F. FLEMING

INFECTIVITY OF UNCONVENTIONAL VIRUSES IN DURA MATER

SIR,-Unconventional viruses cause several fatal spongifonn encephalopathies, including Creutzfeldt-Jakob disease (CJD) and scrapie. Victims harbour the virus in body fluids and tissues, the highest level being in the brain. These viruses are resistant to chemical and physical methods that are generally used to inactivate conventional viruses, and inactivation can be achieved only by autoclaving at 132°C for 1 h or by strong alkali. 12 Contamination of tissue with such viruses

Plasma sodium and clinician’s

assessment

of hydration.

can

be demonstrated only by tedious and

expensive transmission studies to animals. latrogenic transmission of CJD (eg, at brain surgery, electroencephalography with deep electrodes, or corneal transplantation) has been reported,’ and in 1987 a case of CJD in a 28-year-old woman was thought to have