Letters

Acute obstructive hydrocephalus complicating bacterial meningitis

In meningitis, one antibiotic is better than than two

Use of dexamethasone remains contentious

Hydrocephalus was probably non-obstructive

Neuroimaging has limitations

In meningitis, one antibiotic is better than than two

EDITORA recent lesson of the week highlighted the possibility of meningitis in childhood presenting as obstructive hydrocephalus, with cerebrospinal fluid from ventriculostomy proving sterile but subsequent lumbar fluid yielding Streptococcus pneumoniae.¹ In the two paediatric cases described, treatment consisted of both a third generation cephalosporin and benzylpenicillin. In children between 3 months and 18 years of age, however, it is recommended practice for empirical treatment to consist of a third generation cephalosporin alone. ^{2 3} The article may be misleading in giving the impression that use of two antibiotics in this type of case is routine.

There is no sound microbiological basis for using a cephalosporin and a penicillin together, with the exception of patients who may be infected with Listeria monocytogenes. Listeriosis is extremely uncommon in England and Wales, with only 64 reported cases in the first seven months of 1997, including a total of 14 neonatal cases.⁴ A third generation cephalosporin is adequate cover for Neisseria meningitidis, Streptococcus pneumoniae, Haemophilus pneumoniae, or Escherichia coli, and benzylpenicillin provides no extra benefit. Two  lactam antibiotics should not be given together unless this is unavoidable: there is potential for antagonistic interaction between agents, as both act by inhibiting cell wall synthesis. It is not likely that the penicillin was used to cover the possibility of listeriosis, as the drug of choice in such cases is ampicillin (with or without an aminoglycoside).⁵

We recommend that empirical treatment for patients aged between 3 months and 18 years who are suspected of having bacterial meningitis (not thought to be due to listeria or tuberculosis) should be monotherapy with high doses of a third generation cephalosporin, such as cefotaxime or ceftriaxone. Patients in the United Kingdom with a rash typical of meningococcal sepsis may be treated with a high dose of benzylpenicillin alone.

Christopher Settle, Specialist registrar. 
Mark H Wilcox, Consultant.  .
Department of Microbiology, General Infirmary and University of Leeds, Leeds LS2 9JT

1. Mactier H, Galea P, McWilliam R. Acute obstructive hydrocephalus complicating bacterial meningitis in childhood. BMJ 1998; 316: 1887-1889[Free Full Text]. (20 June.)
2. Quagliarello VJ, Scheld WM. Treatment of bacterial meningitis. Lancet 1997; 336: 708-716.
3. Drugs used in the treatment of infections. British National Formulary 1998; 35: 234.
4. Communicable Diseases Surveillance Centre. Listeriosis. Commun Dis Rep CDR Wkly 1997; 7: 332.
5. Jones EM, MacGowan AP. Antimicrobial chemotherapy of human infection due to Listeria monocytogenes. Eur J Clin Microbiol Infect Dis 1995; 14: 165-175[Medline].

Use of dexamethasone remains contentious

EDITORMactier et al illustrate an important complication of bacterial meningitisnamely, acute obstructive hydrocephalus.¹ The authors say that they could not find any record of the incidence of this complication in children. A series of 79 cases over 11 years in Australia has been published; it shows an incidence of 2.8%.²

Interestingly, the first child Mactier et al described did not receive intravenous dexamethasone, whereas the child in the second case did, but when the drug was started, or its role in treating acute obstructive hydrocephalus, was not mentioned. Despite the drug's early promise, its use remains contentious. A recent meta-analysis showed that if it is started with or before parenteral antibiotics, dexamethasone can benefit children with pneumococcal meningitis.³ However, there were limitations on the analysis undertaken.

The use of dexamethasone in meningitis clearly requires further research, but questioning whether it should be used should not delay the administration of intravenous antibiotics.

Asrar Rashid, Clinical fellow. 
New South Wales Newborn and Paediatric Transport Service, Westmead, Sydney 2145, Australia

1. Mactier H, Galea P, McWilliam R. Acute obstructive hydrocephalus complicating bacterial meningitis in childhood. BMJ 1998; 316: 1887-1889. (20 June.)
2. Thomas DG. Outcome of paediatric bacterial meningitis 1979-1989. Med J Aust 1992; 157: 519-520[Medline].
3. McIntyre PB, Berkey CS, King SM, Schaad UB, Kilpi T, Kaura GY, et al. Dexamethasone as adjunctive therapy in bacterial meningitis. A meta-analysis of randomised clinical trials since 1988. JAMA 1997; 278: 925-931[Abstract].

Hydrocephalus was probably non-obstructive

EDITORMactier et al make important points about the management of patients who are seriously ill with acute bacterial meniningitis, particularly about draining cerebrospinal fluid via ventriculostomy.¹ Raised intracranial pressure leading to cerebral herniation is well recognised in patients with bacterial meningitis.² It is probably multifactorial in origin, with inflammatory cytotoxic oedema, interstitial oedema due to increased permeability of the blood-brain barrier, venous thrombosis, infarction, and hydrocephalus contributing.³ Mactier et al, however, refer to "obstructive" hydrocephalus. In fact the hydrocephalus in both cases is likely to be non-obstructive or communicating in origin, as there does not seem to be any evidence for obstruction of the internal cerebrospinal fluid pathway. In particular, figure 3 (computed tomography scan of case 2) shows a dilated fourth ventricle, indicating obstruction ouside the ventricular system. Communicating hydrocephalus in bacterial meningitis reflects failure of cerebrospinal fluid circulation in the basal cisterns and failure of resorption through arachnoid granulations.

The failure to diagnose meningitis on examination of ventricular cerebrospinal fluid is well recognised. Samples of lumbar and ventricular cerebrospinal fluid may show considerable disparity even when the meningeal inflammatory process is severe, and the diagnosis of acute bacterial meningitis should not be discounted when ventricular cerebrospinal fluid is normal or mildly inflammatory. The authors are correct in advising that lumbar puncture should not be performed in patients who have impairment of consciousness before brain imaging.

Finally, the comment that "diagnosing critically high intracranial pressure is difficult" is wrong. Intracranial pressure is easily, reliably, and safely monitored in the appropriate settingwhich is a neurosciences intensive care unit. Although there is no hard proof that such monitoring, the use of ventricular drainage, or other methods of controlling intracranial pressure will improve outcome, it seems logical that the experience and knowledge of those involved in neurological intensive care, particularly with regard to the management of raised intracranial pressure, altered cerebral perfusion, and autoregulation, should be available for patients with bacterial meningitis. Unfortunately the lack of available beds in such units in the United Kingdom may prevent these patients benefiting from modern, targeted treatment.

R Stephen Cooke, Consultant neurosurgeon. 
Victor Patterson, Consultant neurologist. 
Royal Victoria Hospital, Belfast BT12 6BA

1. Mactier H, Galea P, McWilliam R. Acute obstructive hydrocephalus complicating bacterial meningitis in childhood. BMJ 1998; 316: 1887-1889. (29 June.)
2. Horwitz SJ, Boxerbaum B, O'Bell J. Cerebral herniation in bacterial meningitis in childhood. Ann Neurol 1980; 7: 524-528[Medline].
3. Roos KL, Tunkel AR, Scheld WM. Acute bacterial meningitis in children and adults. In: Scheld WM, Whitley RJ, Durack DT, eds. Infections of the central nervous system. New York, Raven Press, , 1991:335-409.

Neuroimaging has limitations

EDITORMactier et al's lesson of the week concludes with a recommendation that all patients with suspected meningitis and decreased level of consciousness should urgently have brain imaging to exclude obstructive hydrocephalus before lumbar puncture.¹ It is most important to understand the limitations of neuroimaging in children with acute meningitis, and to avoid the commonly held misconception that lumbar puncture is safe if neuroimaging is normal.

Lumbar puncture should be avoided in children with clinically diagnosed meningitis if consciousness is impaired or there are clinical signs of raised intracranial pressure, as it may precipitate herniation of the brain or coning. Coning may occur after lumbar puncture in children with meningitis even when neuroimaging has been normal.²

Brain imaging is of no value in the immediate diagnosis of meningitis and is an insensitive method for the detection of raised intracranial pressure.³ The role of brain imaging is to identify complications of meningitis or to exclude focal brain pathology simulating meningitis. Positive indications for computed tomography or magnetic resonance imaging are progressive focal neurological signs, prolonged decreased level of consciousness, prolonged or focal seizures, increasing head circumference, evidence of continuing infection, or recurrence of symptoms. Brain imaging should not be done until antibiotic treatment has been started, raised intracranial pressure has been controlled, and intubation and ventilation started, if necessary.

Laurence Abernethy, Consultant paediatric radiologist. 
Royal Liverpool Children's Hospital, Alder Hey, Liverpool L12 2AP abernet{at}cybase.co.uk

1. Mactier H, Galea P, McWilliam R. Acute obstructive hydrocephalus complicating bacterial meningitis in childhood. BMJ 1998; 316: 1887-1889. (20 June.)
2. Rennick G, Shann F, de Campo J. Cerebral herniation during bacterial meningitis in children. BMJ 1993; 306: 953-955.
3. Heyderman RS, Robb SA, Kendall BE, Levin M. Does computed tomography have a role in the evaluation of complicated acute bacterial meningitis in childhood? Dev Med Child Neurol 1992; 34: 870-875[Medline].