Synopsis
Separate inflammatory cerebral vasculitis from reversible cerebral vasoconstriction syndrome and common mimics, prioritising emergency haemorrhage and stroke assessment before specialist diagnostic and immunosuppressive decisions.
- Reversible cerebral vasoconstriction syndrome typically causes recurrent thunderclap headaches over days to weeks, with or without convexity subarachnoid blood, ischaemic stroke, intracerebral haemorrhage, posterior reversible encephalopathy or seizures.
- RCVS associations include the postpartum period and exposure to vasoactive substances, including sympathomimetics, serotonergic agents, stimulants and some recreational drugs; ask without judgement and document timing.
- Primary angiitis of the central nervous system more often develops subacutely with progressive headache, cognitive or behavioural change, seizures and multifocal neurological deficits rather than repeated stereotyped thunderclaps.
- Multifocal arterial narrowing or beading is not diagnostic of vasculitis: RCVS, atherosclerosis, dissection, infection and technical artefact can produce overlapping angiographic appearances.
- Cerebrospinal fluid is often normal or only mildly abnormal in RCVS, whereas inflammatory change supports—but does not prove—CNS vasculitis after infection and malignancy are considered.
- Early angiography can be normal in RCVS because narrowing may begin distally; evolving symptoms warrant specialist review and sometimes repeat vascular imaging.
- Glucocorticoids are not routine RCVS treatment and observational evidence suggests possible harm; immunosuppression should be reserved for a defensible inflammatory diagnosis under specialist leadership.
- Demonstrating substantial resolution of arterial narrowing by about three months supports RCVS, but follow-up timing and modality should be individualised by neurology and neuroradiology.
Key red flags
Several abrupt maximal-at-onset headaches separated by partial improvement, especially after exertional or vasoactive triggers, strongly suggests RCVS but retains an emergency vascular differential.
Progressive headache with cognitive change, multifocal deficits, seizures or encephalopathy over weeks is more compatible with CNS vasculitis than uncomplicated RCVS and warrants expedited specialist investigation.
Convexity subarachnoid haemorrhage and oedema syndromes often occur early, while ischaemic complications can emerge later; any new deficit or reduced consciousness demands repeat emergency assessment.
Meningism, collapse, neck pain, papilloedema, pregnancy or puerperium, severe hypertension, thrombosis risk and focal deficit can point towards haemorrhage, dissection, venous thrombosis or hypertensive encephalopathy.
Investigation priorities
Identify subarachnoid or intracerebral blood and assess other urgent structural causes of thunderclap headache.
Management branches
Headache reaches peak intensity within seconds to a minute, whether first or recurrent.
- 1. Stabilise ABCDE, record exact onset and triggers, examine consciousness, meningism, optic discs and focal neurology, and check pregnancy or postpartum status.
- 2. Use the local subarachnoid-haemorrhage imaging pathway and add head-and-neck vascular imaging when RCVS, dissection, aneurysm or stroke is plausible.
- 3. Escalate any haemorrhage, infarct, seizure or hypertensive emergency immediately; investigate a negative initial scan further when clinical suspicion remains.
- 4. Review prescribed, over-the-counter and recreational vasoactive exposures, but do not let a plausible trigger prematurely close the differential.