Meningitis: The Eternal Headache

Too many myths to list, but maladies:

• The pre-test probability of meningitis in most patients is pretty low.
• Stop using the word meningoencephalitis, except in some very rare circumstances
• Get an LP ASAP, and do you really need that CT brain before the LP?
• Nothing should delay antibiotic administration. And this is one of the few conditions where you might get to use IV chloramphenicol.
• No, the patient with meningitis doesn’t require acyclovir, but dexamethasone is recommended.

Loyal readers, I must apologise before beginning our tirade at hand. Some of you have labelled me the Judas Iscariot of bedside dogma – betraying long-held clinical rituals with reckless evidence and irreverent tone. Imagine my horror at being accused of using evidence in medicine. I’ll give you a moment to clutch your pearls.

Today’s topic is a diagnosis that gets uttered reflexively at the altar of fever and headache. Meningitis: feared, overdiagnosed, and often managed with more superstition than science – the boogeyman lurking behind every photophobic glance. So, in the spirit of making no new friends, let’s embark on a polite demolition of the fables surrounding those with stiff necks and severe enough headaches.

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1. Meningitis is common

Perhaps it was, in the 19th century. In our post-vaccine world however, we’re looking at a rate of ~1 case per 100,000 people in developed countries. Viral meningitis is perhaps slightly more common. In Australia, there is only recent data on incidence of meningococcal disease, clocking in at 0.3 per 100,000 in 2021 [1]. Most of us will encounter only a handful of true cases in our careers. Yet we behave as if every mildly “photophobic” 24-year-old with a hangover and a “low-grade temperature” of 37.6°C is about to internally combust with Neisseria. The cognitive dissonance is easily justified – no one wants to miss meningitis. And it’s really not our fault. 

The triad of fever, neck stiffness and change in mental status was only present in 44% of patients in one Dutch study (it is from 2004 but still) [2]. In fact, I would like to see someone quantify the deleterious effects on education and diagnosis that grouping every condition into “triads” has had. For example, in the same study, 95% of patients had ≥ 2 of fever, neck stiffness, change in mental status or headache. Not to add to the chaos, but the diagnostic value of the eponymous signs named after a couple of white dudes with moustaches, are also abysmal (Table 1).

There is a new kid on the block, the jolt accentuation, where if a simulated heavy metal concert worsens their headache, then it scores them an LP. A Cochrane review on this was inconclusive and suggested you can’t rule out meningitis if negative [3]. The advice of the brightest minds is to take a good history from the patient with impaired consciousness and do a thorough neurological exam (because we have the time in ED) [4]. Clearly, we need some better tools.

Table 1. Diagnostic performance of some eponymous signs in adults. More on common myths around sensitivity and specificity in another episode.

	Sensitivity	Specificity	PPV	NPV
Neck stiffness	31%	71%	41%	61%
Kernig’s sign	11%	95%	60%	60%
Brudzinski’s sign	9%	95%	50%	62%

Data from Brouwer et al. 2012 [4]

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2. Meningoencephalitis is even more common

The use of this word scores you a prime spot on my burn book, though by now you know you’re in good company. I’m not arguing that the simultaneous inflammation of the meninges and encephalon is impossible. However, meningism plus confusion doesn’t translate to a brain on fire. Just because two words easily form a portmanteau, doesn’t mean you sound impressive when you use it. The predominant cause of encephalitis is HSV. This patient typically presents with confusion, seizures, personality changes. A bit like me, when I hear the term meningoencephalitis. In seriousness, it can happen but like meningitis itself, common it is not. Here, antivirals are often a bigger consideration. 

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3. Lumbar punctures lead to coning

LPs theoretically cause a pressure gradient between the brain and the site of puncture. All of our evidence for coning comes from the 20th century, and many of these patients were already unwell enough to cone [5]. I know CTs are crucial in the work-up of papercuts, but they are unfortunately not manometers and cannot measure ICP. The evidence on this is clear (check out [6] for another great resource, and our informal competition).

There are very few reasons to get a CT prior to an LP – and if this is happening, give antibiotics first – but here’s a non-exhaustive list:

• Focal neurological signs
• Presence of papilloedema (if you know how to use an ophthalmoscope)
• New seizures
• GCS ≤ [REDACTED] (this value is so variable across guidelines that it is impossible to suggest a consistent number)
• Immunocompromise – increases risk of space-occupying lesions

Another consideration these days is that patients are 60% water and 40% apixaban or clopidogrel. Given these are relative contraindications in an emergency setting, they do require a discussion with a Haematologist (refer to [7] for a great resource on this). And if this is happening, give antibiotics first.

Ultimately, the LP is essential. It’s in fact a largely low risk and well-tolerated procedure (if done appropriately). Even if it cannot be done prior to antibiotics, it should be done within 4 hours.

Outside of the tests you already know of, do a CSF lactate. If done prior to commencing antibiotics, it has a high negative predictive value which can rule out bacterial meningitis [8].

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4. Acyclovir saves lives

Yes, and seatbelts too – just not in people already out of the car.

Aciclovir in fact has no good evidence in HSV meningitis, but its use can perhaps be justified, especially in immunocompromised patients [9]. But in other cases of viral meningitis, there is no role for aciclovir. The most common cause of viral meningitis is enteroviruses. The treatment for these, and basically all the others, is supportive. But of course we must feel responsible for people’s recovery, especially if they are immunocompromised, and who cares if the patient gets an AKI right? We’ll just blame their dehydration secondary to being unwell.

The use of dexamethasone, I can get more behind. Guidelines suggest starting it before antibiotics even. It can decrease rates of hearing loss and neurological sequelae [10]. Interestingly, it’s a Republican – it seems to only benefit patients in rich countries [10]. Its benefits on mortality also only apply to S. pneumoniae meningitis, and the NICE guidelines only recommend use for pneumococcal or H. influenzae type b [11]. So you can stop it once you have the species [see eTG].

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I promised you IV chloramphenicol (yes, that’s chlorsig for the eye guys)

In cases of severe beta lactam allergies – after clarifying the hell out of this supposed allergy (an impending Myths and Maladies topic) – the UK NICE guidelines recommend IV chloramphenicol for the treatment of meningitis.

Giant’s Shoulders:
For this I refer you to some of my favourite resources. This episode was inspired by one of my favourite podcasts – ID:IOTS, and the work of Dr Fiona McGill.
British Infection Association – Investigation of Meningitis and Encephalitis 2024
[11] NICE Meningitis Guidelines – https://www.nice.org.uk/guidance/ng240
eTG on the treatment of Meningitis

Also cited above:
[1] Lahra et al. Australian Meningococcal Surveillance Programme Annual Report. 2024.
[2] van de Beek et al. Clinical features and prognostic factors in adults with bacterial meningitis. N Engl J Med. 2004;351(18):1849-59.
[3] Cochrane on the jolt manoeuvre
[4] Brouwer MC – aptly titled ‘Dilemmas in the diagnosis of acute community-acquired bacterial meningitis‘
[5] A paediatrics-focused take on the LP / coning / CT story
[6] The delightful Things We Do for No Reason series takes on CT before LP
[7] Definitive Association of British Neurologists Clinical Guideline on periprocedural antithrombotic management for LPs
[8] Buch K et al in praise of the CSF Lactate
[9] A survey among ID docs across the world on acyclovir for meningitis
[10] Cochrane takes on steroids and meningitis