Clinical Case 107: Subarach Sans Scan
This case is inspired by a Twitter conversation started by Dr Brent May ( @DocBrent ) – he is an Anaesthetist and motorsport doc in Australia.
Brent asked the simple question: “SAH Q – no CT available. What is the “usefulness” of RBC count on LP? Lab “unable to do xanthochromia”. This is a real problem in many hospitals – especially the smaller places with no CT or specific lab crew. So lets look at a case and try to get to the bottom of this one!
You are working in a remote clinic with a small Emergency area. It is a slow day. You are 400 km from the closest hospital which has a CT and laboratory services.
Jan is a 45 year old local woman. She presents with a bad headache – this is not usual for her, she is not usually a “headachy” person. No PMHx of migraine or other headache syndrome. It woke her from sleep this AM – about 4 hours ago. Maximal intensity from the onset. She says it has not responded to simple analgesia and resting at home. She has had no syncope or neurological symptoms. The headache has remained relatively constant. She is complaining of neck stiffness – though has normal ROM in her neck. She has no fever, vomiting or photophobia.
On examination she has no neurological signs. Her obs are all normal, BP = 140/85, afebrile. You cannot reproduce any objective neck stiffness.
So – first question. Based on that clinical info – what would you estimate Jan’s “probability” of having a subarachnoid haemorrhage ? Have a Gestalt guess… 2%, 5%, 10%, 50 %???
How low would you want your “probability” to be to avoid a transfer and subsequent work-up? i.e.. what is your lower test threshold for SAH? 1:100, 1: 1000, less?
Here is a copy of Perry & Steill’s landmark paper in the BMJ 2011 – check out tables 1 & 2. Jan is pretty much a “average Jan” for the cohort of 3000 pts in their paper.
About 7.7 % ended up having a subarachnoid bleed – and another 2 – 3 % had another non-benign cause for their headache. So 10% is a reasonable “pretest probability” for badness in Jan’s case.
Now a 10% risk of serious intracranial pathology. That would mandate a work up in most places. Unfortunately your hospital only has rudimentary lab gear – you can do an LP and get red cell counts, but not xanthochromia. A CT would be helpful if you can do it in less than 6 hours – but even if you called for transfer now – it would be well past 6 hours by the time Jan made it into the doughnut 400 km away.
So here we are. You can do an LP and get red cell counts on the CSF. Xanthochromia is probably not helpful as it is early (less than 12 hours) and simple visual inspection for yellow change is inaccurate. [Best read by non-colour blind female lab techs apparently! Can you ask for that on the forms?] Most Australian labs use automated spectroscopy to analyse for xanthochromia – and this is usually only available in larger, tertiary labs.
The accepted gold standard diagnostic features of SAH are variable – but the Canadian group who do a heap of research use the following:
“Subarachnoid haemorrhage was defined by:-
– subarachnoid blood on unenhanced computed tomography of the head, OR
– xanthochromia in the cerebrospinal fluid, OR
– red blood cells (>5×106/l) in the final sample of cerebrospinal fluid,
PLUS an aneurysm or arteriovenous malformation evident on cerebral angiography.”
So now the big question. Is there any way that you can effectively “rule out” SAH in Jan without transferring her 400 km to the next hospital?
Does a low CSF red cell count allow us to “exclude” SAH? Can we use any other tests to decrease the risk for Jan?
Tough yet common problem in many rural areas in Australia. I would love to hear your thought and comments below. Does it depend on the timing? Can we watch and wait if the initial LP is clear? Or do we need to get imaging and a review for xanthochromia on all the Jan’s we see in ED?
If you are interested in the diagnostic dilemma that is the “SAH work up” then I highly recommend listening to David Newman’s SMART EM episode on the topic from way back in 2010. (WARNING: it is nearly 2 hours of podcast!)
Let me know what you think
I am a bit rusty, but I know these types of situation come up on a fairly regular basis, even in small hospitals in the USA (i.e. cath labs, etc.)
Especially, in the USA, if the patient has no money or insurance. Things may change a bit with Obamacare, but doubt it.
At any rate, I would mildly medicate, and observe with bed rest in a dark room. Prepare as best you can for transfer, alerts, etc.
After all, what is a neurosurgeon or neurologist going to do, if you rush this patient to the nearest facililty? Would they give Thrombolytics in the facility? It has been a while for me, and I don’t know Australia’s standard of care, or here too, matter of fact.
But in my day, no thrombolytics were being given, and the few patients I did speak to about it, did not want to try it.
john bennett md
I think SAH diagnosis can be a dilemma but not in this situation. This patient needs to go to a bigger hospital. She could have had an ICH into an AVM / undiganosed tumour or secondary to HTN, and the LP might be negative in that case. And if she had a SAH, she needs a CTA to look for the source and literature shows that she might be better off in a bigger centre http://www.ncbi.nlm.nih.gov/pubmed/24979097.
Careful with the CT within 6 hours as well. While our patient is “the average Jan”, the CT in our hospital is unlikely to be the “average CT ” in the BMJ study – high resolution CT is not available in the great majority of Australian non-tertiary hospitals.
As for red blood cell count, if xantochromia is not available, CSF needs to be collected in 3 containers. If the RBC decreases from tube 1 to 3 and is 0 in tube 3, SAH can be ruled out.