Differentiating Subarachnoid from Benign Headache
One of the things I strongly dislike, is when a patient comes into the emergency department with a complaint of headache and it has features of a subarachnoid haemorrhage(SAH), and I just dont know if it is or not, so I err on the side of being careful and CT and LP.
When we read the studies, a SAH doesn’t have to be ‘the worst headache’ that patient has ever had, nor does it have to come on instantly. I used to ask, “is it really bad?” and “Did it come on…like…BANG, being hit on the back of the head with a shovel?” I still ask these questions, but am less likely to rule out SAH. I will talk more about this at the EMCORE.
In fact, we miss about 5-6% of SAH in the emergency department (Vermeulen et al Stroke 2007;38:1216-21). This isn’t great, as about 50% of patients with Grade I SAH die and of the remaining patients, only 50% get back to their previous level of functioning.
So, first and worst, doesn’t count. What can we use? Linn et al(JNeurol Neurosurgand Psychaiatry 1998;65:791-93), tell us that if we are suspicious of a headache and it is new, and has onset within 5 minutes and lasts longer than an hour, it should concern us and we should investigate the patient for a SAH.
Now remember, we aren’t talking about the patient with a depressed level of consciousness, or neurology. Those patients you’re going to scan. We are talking about the patient with headache as their only complaint.
Well here is study in the BMJ(2010) by Perry et al. It was a prospective, multicentred, cohort study over 5 years. It enrolled 1999 patients with a non-traumatic headache. The study identified markers that could be used to determine a clinical rule with 100%sensitivity. I will say at the outset that this study had some significant limitations, one of which was that 1050 patients identified as eligible were not included in the study.
Any loss of consciousness, Stiff neck, Age > 40, Came on during exertion, Patient was brought to the ED by ambulance, Vomiting, High blood pressure > 160systolic, or >100 diastolic
Remember, none of these have been validated yet but interesting.
A few points on investigation
The approach, unfortunately, is still Non-contrast CT brain, if normal, followed by lumbar puncture, if we are suspicious of a SAH, until a validated rule is found. The key is when to do the lumbar puncture. Some people wait for 12 hours to do an LP, primarily waiting for xanthochromia to develop, ie., the patient is there, waiting, for 12 hours. The reality is that, the sample is usually looked at under a light by the lab tech, who makes a visual judgement on whether the sample looks clear. Very few centres have spectrophotometers, and the reason is, that the band-width is set at such a level, so that no SAH’s are missed, that there is a significant false positive rate. The other concern is that there are a number of ultra-early re-bleeds that occur, yes, within the 12 hours.
Due to this, red cell analysis has been used. There needs to be adequate time (1-2 hours)for red cells to track down the canal, however, following this, red cells may help. The arguments about decreasing red cell count and our inability to judge traumatic taps is real, however, the red cell approach is receiving greater acceptance. Is it better than the guy in the basement, looking at the sample against a fluro light? I’m not sure.
The reality, is that in most cases, if you are concerned, you will still discuss this patient with the neurosurgery unit anyway. Now, if you think that will solve all problems, then you’re wrong. I don’t know how many variations of approaches I have encountered over the years. It depends on who I speak to, but they range form “Transfer for MRI”, to “Do a CT angiogram”, to “Send the patient home for outpatient MRI”, to “Can you pick up my laundry, I’m stuck in theatre and I’m a neurosurgeon and then I’ll tell you”, to I do’t know what.
The evidence is the evidence and I’m getting it all together. I’m presenting it at EMCORE and we’ll get a video of that lecture up soon afterwords.