Authors' reply: Subarachnoid haemorrhage: lumbar puncture for every negative scan?
Coats suggests that a lumbar puncture should not be undertaken
following a negative computed tomogram for every patient with ‘query
subarachnoid haemorrhage’.1 We robustly disagree.
Firstly, in his Bayesian calculations, Coats used the sensitivity of
computed tomography for identifying subarachnoid blood at 12 hours after
headache onset (98%). Sensitivity decays rapidly within days,2 so patients
who do not present immediately, or who have to wait for their computed
tomogram, are less likely to be identified and the importance of a
subsequent lumbar puncture cannot be overstated. Furthermore, computed
tomography is often interpreted by junior, non-specialist radiologists,
who are more likely to miss subtle signs of subarachnoid blood than senior
specialist neuroradiologists. We see a steady trickle of patients whose
subarachnoid haemorrhage was identified in a district general hospital on
the basis of a lumbar puncture, after a normal report of their scan, but
review of the scan confirms the presence of subarachnoid blood. These
patients would not have been diagnosed, and might subsequently have had a
fatal re-bleed had the clinicians not done a lumbar puncture.
Secondly, Coats assumes lumbar puncture is performed only to exclude
subarachnoid haemorrhage, yet it may be the key to diagnosing other causes
of sudden headache, such as meningoencephalitis and intracranial venous
thrombosis (box 2 of our review2).
Lastly, we are intrigued by the notion that doctors might enter into
a Bayesian debate with a frightened, distressed, vomiting patient in the
hectic environment of the Emergency Department. Without wishing to sound
paternalistic, patients are likely to prefer their doctors to quickly and
accurately diagnose what is wrong with them, rather than debate the merits
of not conducting a low-risk diagnostic procedure for a potentially life-
threatening neurological disease.
In a perfect world, all patients with sudden onset headache would
present immediately to senior specialist medical attention, and lie
completely still in a modern generation scanner performed within 30
minutes of their first assessment, which is then immediately interpreted
by an experienced consultant neuroradiologist. Acknowledging that such a
state does not exist, we stand by our recommendation that all patients
with a headache of maximal intensity either immediately or within minutes,
lasting longer than an hour, and who have received a normal computed
tomogram report, should undergo lumbar puncture.2
<P> 1 Coats TJ. Subarachnoid haemorrhage: lumbar puncture for
every negative scan. BMJ 2006;333:396-397
<P> 2 Al-Shahi R, White PM, Davenport RJ, Lindsay KW. Subarachnoid
haemorrhage. BMJ 2006;333: 235-40
Competing interests: RJD and KWL have acted as expert witnesses in cases involving subarachnoid haemorrhage. PMW has received reimbursement for expenses in attending international conferences from Siemens, Cordis, Boston Scientific, UK Medical, and Microvention; has been reimbursed by Pyramed UK for running an educational programme; and holds a research grant from Microvention funding a randomised controlled trial (hydrocoil endovascular aneurysm occlusion and packing study). PMW has received consulting fees from Boston Scientific, Cordis, UK Medical, and Microvention.
Competing interests: No competing interests