Subarchnoid haemorrhage Assessment and Investigation25TH AUGUST 2016ROSALIND OAKES

Introduction The Textbook Presentation

Diagnostically more difficult …Patient GCS 15 with no focal neurological deficit

Meta analysis Carpenter et al (2016)◦ The significance of the clinical assessment◦ Investigation choices◦ Should we LP following negative CT?

NB this talk is only relevant to spontaneous SAH

PrevalenceHeadache is 1% of presentations to ED.

10% of the headache patients will have a history concerning for SAH i.e. those with a severe, abrupt-onset headache (LITFL)

Of the headache presentations 1% will have SAH.

Therefore, of patients with a concerning history, 10% have SAH.

The typical patient◦ 45-64 years old age

◦ 85% are caused by intracranial aneurysms.◦ Risk factors for these are HTN, smoking, Personal or First degree relative with SAH, connective

tissue disorders e.g. PCKD and neurofibromatosis

◦ 10% are non aneurysmal perimesencephalic haemorrhage (usually benign, low pressure, cons mx)

◦ 5% are due to rare causes◦ Drugs> amphetamines, cocaine and blood thinners, AV malformation, vasculitis

Assessment History

◦ A less severe headache hours to days before the large bleed (‘sentinel haemorrhage’) occurs in 50%. Still usually occurs abruptly but often responds to analgesics.

◦ 95% of patients will have a headache, severe sudden onset reaching peak intensity instantaneously

but include peaking between seconds to 60 mins

◦ Brief or continuing loss of consciousness occurs in the majority

◦ One third will develop the headache during exercise including bending or lifting

◦ Seizure in association with the typical headache is a good indicator of SAH

◦ 75% have nausea and vomiting

◦ Neck pain or stiffness is common

Examination 2/3s have impairment of consciousness

75% will have signs of meningism, photophobia and neck stiffness

25% will have focal neurological deficit

Systemic features; fever, severe HTN, hypoxia and ECG changes that mimic AMI

Prognosis ‘A high stakes condition without a clear cut presentation lurking within a high volume complaint, and ultimately most patients do not have a serious diagnosis’

SAH has a 40-60% mortality rate from initial haemorrhage with one third of those that survive having a significant deficit (50% do not return to work)

Carpenter et al (2016) Spontaneous Subarachnoid Hemorrhage: A Systematic Review and Meta-Analysis Describing the Diagnostic Accuracy of History, Physical Exam, Imaging, and Lumbar Puncture with an Exploration of Test Thresholds

Acad Emerg Med. 2016 Jun 16

5022 citations in the initial search, 122 full text review and 22 were analysed finally.

How is useful is the clinical assessment?

Examination

Neck stiffness was strongly associated with SAH as reported in three studies. Sensitivity 0.29. Specificity 0.96. (LR+ 6.59, 95% CI 3.95-11.00) i.e. Quite good at identifying patients without the disease

Focal Neurological deficit: Sensitivity 0.31 and Specificity 0.93

‘No single history or physical exam finding significantly increases (LR+>10) or decreases (LR- < 0.1) the post-test probability of SAH for severe headaches that peak within one hour of onset.’

‘Many elements of history and physical exam for SAH have only fair to good inter-physician reliability, with the characterization of the headache as “thunderclap” being one of the least reproducible findings.’

Investigation: CT brain Older CTs were thought to miss 5% of SAH, hence the need for LP

However, newer scanners are more accurate

Pooled data from 2 studies Perry (2011) and Backes (2012)

CT > 6 hours will correctly identify all patients without the disease (true negatives) but some with SAH will not be detected (false negatives)

Further investigations Traditionally the next test following a negative CT is an LP

◦ Problems with LP◦ The test is moderately accurate for SAH - equivocal result (15-20%)◦ Traumatic LP (blood contaminated) occurs 1 in 6◦ Failure of procedure◦ Post-LP headache (up to 40%), ◦ low back pain, local infection or traumatic neurology◦ Xanthochromia takes hours to develop therefore timing affects interpretation. LP > 12 hours

post headache to most reliably differentiate from a traumatic tap

Some patients will be told that they have may have SAH and need further investigation when they are disease free. (False positives)

LP Discussion >6 hours: For patients with negative CTs, 17/1546 (1%) turned out to be false negatives following LP. (Perry et al)

Number needed to LP to identify one SAH is 91. None of those identified had aneursymal SAH and none had surgery. (Brunell et al)

LP provided an alternative diagnosis in 3% of suspected SAH cases. (Brunell et al). 227 LPs to identify 1 CNS infection requiring antibiotics.

An alternative option is to proceed to CT angiography which are good to detecting aneurysms. Issues are that berry aneurysms are common (1-2%) of the population and identifying an unruptured one in a patient may have not be helpful in determining the cause of that patient’s headache.

Pre & Post LP probability of SAH for patients >6 hours

Pre CT probability is 7.5% (based on the prevalence in this meta analysis)

Negative likelihood ratio (i.e if the CT is negative) the probability of the patient having SAH is reduced to 0.564%

The patient proceeds to LP.

If the LP is negative the probability of them having SAH is 0.07%

Test treatment threshold

Benefits of treating an aneurysmal SAH versus risks/limitations of the test to diagnose it:

LP is likely to benefit only patients within a narrow band of pre-LP probabilities, around 2% to 7%.

Since CT is such an accurate test this equates to pre-CT probabilities of 20% or higher. (Much higher than what we would expect)

Comments Some of the paper is very theoretical – e.g. calculating the numerical probability of SAH following history and examination.

Differentials for a sudden onset headache are not discussed◦ Haemorrhagic stroke or other bleeds◦ Vascular dissection◦ Sinus thrombosis◦ Acute hydrocephalus◦ Migraine◦ Cluster Headache

Summary

The authors conclude that within 6 hours of headache onset, CT demonstrates sufficient accuracy to rule-in or to rule-out SAH

References Carpenter et al (2016)Spontaneous Subarachnoid Hemorrhage: A Systematic Review and Meta-Analysis Describing the Diagnostic Accuracy of History, Physical Exam, Imaging, and Lumbar Puncture with an Exploration of Test Thresholds

Acad Emerg Med. 2016 Jun 16

Textbook of Adult Emergency Medicine, 4th Edition (2014)

Authors Peter Cameron, George Jelinek, Anne-Maree Kelly, Anthony F. T. Brown & Mark Little

ISBN : 9780702053351

http://omerad.msu.edu/ebm/Diagnosis/Diagnosis7.html

Likelihood Ratios Calculated using sensitivity and specificity of the test

LR + is how much to increase the probability of the disease if the test is positive

LR- how much to decrease the probability of the disease if the test is negative

E.g. Calculate your pre test probability based on your history and then examine the patient for neck stiffness. If they have neck stiffness then how much does this increase the probability that they have SAH?

One rule of thumb is that LR+ >10 and LR- < 0.1 provide considerable diagnostic value.

An LR of 1 does not change the post test probability at all

How to calculate post test probability using