a diagnostic approach to the adult with acute headache

the following is a STEPWISE diagnostic algorithm provided as an AID to diagnosis of headache in the adult patient - one should not just jump to step x without considering each of the preceding steps

does the patient have a clinical picture of meningitis?
- ie. headache + fever + neck stiffness +/- photophobia
- NB. not all patients with meningitis will have all of the above, and most patients with headache and fever alone will have other infections such as influenza, etc.
- these patients must be assessed ASAP and considered for immediate empirical antibiotics and Mx as per suspected meningitis
is there decreased mental state, collapse, syncope, new onset seizures, new focal neurology or sudden onset headache?
- these patients must be assessed ASAP and have an early CT scan to exclude:
  - subarachnoid haemorrhage (SAH)
  - stroke (CVA)
  - traumatic intracranial haemorrhage if history of trauma
  - other causes of raised intracranial pressure (ICP)
  - NB. DDx also includes benign post-coital or orgasm headache (usually resolves within 30-180min), but SAH may occur during orgasm so still need to exclude it!
is the patient on an anticoagulant such as warfarin and may have had a head strike?
- these patients generally should have a CT scan to exclude traumatic intracranial haemorrhage, and if present have their anticoagulant state reversed if possible
have they had a head injury and are now showing high risk features?
- see head injury in the adult patient
does the patient have a known unusual medical condition or high risk condition or medications?
- these patients will probably need an experienced clinician to evaluate
- eg. immunocompromised patients including those with HIV / AIDS have higher risk of unusual infections
does the patient have a painful red eye?
- consider acute glaucoma as this needs immediate Rx
is the headache the same as previous migraine headaches the patient has had?
- it is probably migraine and if there are no other red flags, Rx as such
is the headache unilateral?
- see acute unilateral headache
is it post-ictal in a patient with known epilepsy?
- probably a post-ictal headache
is it bilateral frontal headache?
- consider:
  - sinusitis
  - brain tumour - if chronic and pain on wakening, worse on Valsalva
is it mainly occipital?
- consider:
  - hypertension (diastolic > 130mmHg)
  - posterior brain tumour - if chronic and pain on wakening, worse on Valsalva
  - cervicogenic headache
is it a generalised headache?
- has the patient had a recent LP - see post LP headaches (PLPH)
- has the patient been to high altitudes > 3000m - consider altitude sickness
- if febrile illness, consider:
  - toxic metabolic headache associated with any fever
  - infections well known to cause headaches as a prominent feature such as influenza, COVID-19 coronavirus (2019-nCoV / SARS-CoV-2), Legionella (Legionaire's disease)
- if no fever, consider:
  - benign intracranial hypertension (pseudotumour cerebri)
    - usually, young, obese female with amenorrhoea or irregular cycles or on tetracyclines
    - check for papilloedema and do CT scan
  - tension headache
  - drug-related headache eg. nitrates
  - carbon monoxide poisoning
  - hypoxia
  - hypercapnia
  - acute anaemia
  - analgesic abuse headache
other causes of thunderclap headaches:
- this assumes SAH has been adequately excluded by CT brain +/- LP
- coital / orgasm headache
- reversible cerebral vasoconstriction syndrome (RCVS)
  - can occur over days to weeks
  - can also present with other symptoms such as seizures, strokes, and brain oedema
  - Dx: magnetic resonance angiography may can reveal the characteristic “string of beads” appearance of the affected arteries.
  - may be precipitated by:
    - vasoactive aubstances: such as certain medications (e.g., selective serotonin reuptake inhibitors, decongestants), recreational drugs (e.g., cocaine, cannabis), and acute migraine medications
    - hormonal changes during pregnancy and the postpartum period
    - eclampsia and pre-eclampsia
    - endothelial dysfunction may play a crucial role in the pathogenesis of RCVS. This dysfunction may lead to impaired regulation of cerebral arterial tone and contribute to the reversible vasoconstriction observed in the syndrome
    - sympathetic overactivity
    - severe hypertension, infections, autoimmune diseases, and certain medical procedures or conditions that affect cerebral blood flow

see headache for general indications for CT scan in the patient with headache, and for general workup of the patient with headache in the ED