Overview

Reversible Cerebral Vasoconstriction Syndrome (RCVS) is a neurovascular condition characterized by severe, recurrent thunderclap headaches and multifocal segmental vasoconstriction of the cerebral arteries that resolves spontaneously within three months. Its clinical and radiographic overlap with primary angiitis of the central nervous system (PACNS) and other cerebral vasculopathies creates a diagnostic challenge with significant therapeutic consequences: RCVS is generally managed with supportive care and trigger avoidance, while PACNS requires immunosuppression with corticosteroids and cyclophosphamide. Administering immunosuppression to a patient with RCVS can be harmful; conversely, withholding it from a patient with PACNS allows progressive inflammatory injury.

The RCVS₂ score was developed and validated by Rocha, Singhal, and colleagues (Lancet Neurology, 2019) to provide a standardized, quantitative tool for distinguishing RCVS from other cerebral vasculopathies at the time of initial presentation, before the characteristic spontaneous vascular normalization that confirms RCVS retrospectively. The score is derived from five clinical and imaging variables, achieves a sensitivity of approximately 90% and a specificity of approximately 99% for RCVS at a threshold greater than 5, and has been externally validated across multiple international cohorts.

Background: Reversible Cerebral Vasoconstriction Syndrome

Definition and Nomenclature

RCVS encompasses a group of conditions previously described under a variety of names, including Call-Fleming syndrome, benign angiopathy of the central nervous system, postpartum angiopathy, migrainous vasospasm, drug-induced cerebral arteritis, and thunderclap headache with reversible vasospasm. The unifying term "reversible cerebral vasoconstriction syndrome" was proposed by Calabrese and colleagues in 2007 to emphasize the defining triad: thunderclap headache, multifocal cerebral vasoconstriction on vascular imaging, and spontaneous resolution of both within 12 weeks.

Epidemiology

RCVS affects predominantly women (approximately 70 to 80% of cases), with a peak incidence in the fourth and fifth decades. It may occur at any age, including in children and older adults. The true incidence is unknown because mild cases likely resolve without formal diagnosis, but RCVS is now recognized as among the most common causes of thunderclap headache in adults, and is substantially more common than PACNS.

Population-based studies suggest RCVS may account for 50% or more of all thunderclap headaches evaluated in dedicated neurovascular centers. Its incidence appears to be increasing, in part due to greater clinical recognition and the expanding use of vasoactive substances implicated as triggers.

Pathophysiology

The precise mechanism driving RCVS remains incompletely understood. The prevailing hypothesis centers on a transient disturbance in the regulation of cerebrovascular tone, resulting in episodic vasoconstriction affecting medium and large cerebral arteries. Proposed mechanisms include:

• Sympathetic nervous system dysregulation: Evidence suggests a state of adrenergic hyperactivation, possibly related to surges in catecholamines (endogenous or exogenous), leading to intense arterial smooth muscle contraction. This explains the strong association with vasoactive drugs and the postpartum state.
• Endothelial dysfunction: Transient impairment of nitric oxide-mediated vasodilation has been proposed. Some studies report low serum nitric oxide metabolite levels during the acute phase of RCVS.
• Blood-brain barrier disruption: In cases complicated by posterior reversible encephalopathy syndrome (PRES), vasogenic edema indicates failure of cerebrovascular autoregulation and blood-brain barrier breakdown, suggesting that endothelial injury may precede or accompany vasoconstriction in some patients.
• Hormonal influences: The predilection for women and the well-established postpartum trigger suggest a role for sex hormones in modulating vascular tone, possibly through effects on endothelial nitric oxide synthase activity or smooth muscle contractility.

Regardless of the initiating trigger, the vasoconstriction in RCVS is dynamic and migratory: it typically begins distally in small cortical branches and propagates centripetally toward larger proximal vessels over a period of days to weeks. This centripetal progression distinguishes RCVS from PACNS, where vasoconstriction tends to be more random, fixed, or associated with vessel wall enhancement on high-resolution MRI.

Clinical Presentation

Thunderclap Headache

The hallmark of RCVS is the thunderclap headache (TCH): a severe headache reaching maximal intensity within 60 seconds of onset, often described as "the worst headache of my life." In RCVS, TCH is typically recurrent, occurring in clusters over days to two to three weeks before gradually subsiding. The recurrent nature is a key distinguishing feature from aneurysmal subarachnoid hemorrhage (SAH), where a single sentinel TCH is the rule.

TCH in RCVS is frequently triggered by physical or emotional stimuli: sexual activity (coital cephalalgia), Valsalva maneuvers (coughing, straining, weight lifting), sudden emotional stress, bathing or showering (cold water exposure), and physical exertion. Up to 75% of patients can identify a specific trigger for individual headache episodes. Between attacks, patients may have a persistent dull background headache. Nausea, vomiting, photophobia, and phonophobia are common.

Neurological Deficits

Most RCVS episodes resolve without permanent neurological sequelae, but in up to 10 to 15% of cases, ischemic or hemorrhagic complications occur:

• Convexal subarachnoid hemorrhage (cSAH): Non-aneurysmal hemorrhage over the cerebral convexities, not in the basal cisterns. This is the most common hemorrhagic complication of RCVS and reflects vasoconstriction of small cortical surface vessels.
• Cortical spreading depolarization and PRES: Posterior reversible encephalopathy syndrome occurs in approximately 9 to 38% of RCVS cases and manifests as seizures, visual disturbances, altered consciousness, and vasogenic edema on MRI, predominantly in the posterior cerebral watershed zones.
• Ischemic stroke: Occurs in approximately 4 to 12% of RCVS cases, typically in the territory of the middle or posterior cerebral arteries, resulting from severe, prolonged vasoconstriction. Strokes from RCVS tend to occur later in the clinical course (after the first week) as vasoconstriction progresses centrally to involve large vessels.
• Intracerebral hemorrhage: Rare; may occur in the context of severe vasoconstriction with reactive hyperemia and blood-brain barrier failure.
• Cerebral venous thrombosis: An uncommon but reported association, particularly in the postpartum period, requiring careful MR venography evaluation.

Triggers and Associated Conditions

A broad range of triggers have been associated with RCVS. Their identification is clinically important because trigger avoidance is central to management and because trigger presence (the "V" variable in RCVS₂) strongly supports the diagnosis:

• Vasoactive/sympathomimetic drugs: Serotonergic agents (triptans, SSRIs, SNRIs), ergot alkaloids, pseudoephedrine, phenylephrine, cocaine, amphetamines, methylenedioxymethamphetamine (MDMA/Ecstasy), cannabis (particularly high-potency synthetic cannabinoids), nicotine patches, and dietary supplements containing synephrine or tyramine.
• Postpartum state: One of the strongest and most consistent triggers. RCVS occurring in the postpartum period (typically within the first week after delivery) is associated with preeclampsia/eclampsia, oxytocin use, bromocriptine (used for lactation suppression), and ergometrine administration.
• Immunosuppressive and chemotherapy agents: Tacrolimus, cyclosporine, bevacizumab, and intravenous immunoglobulin have been implicated.
• Selective serotonin reuptake inhibitors: Although the association is debated, SSRIs and SNRIs used for depression or anxiety appear to be mild risk factors.
• Blood transfusion and red cell transfusion: Reported in sickle cell disease and other hemoglobinopathies.
• Surgical procedures: Carotid endarterectomy, neurosurgical procedures, and general anesthesia with vasoconstrictive agents.
• Hypercalcemia and pheochromocytoma: Endocrine causes of catecholamine excess.
• Spontaneous (idiopathic): In 25 to 40% of cases, no identifiable trigger is found.

The RCVS₂ Score: Development and Validation

Study Design and Derivation Cohort

The RCVS₂ score was developed from a retrospective cohort of 206 patients with either RCVS (n=110) or a comparator vasculopathy (n=96, predominantly PACNS) evaluated at three tertiary referral centers in the United States, Canada, and France. Variables associated with RCVS versus comparator diagnoses on univariate analysis were entered into a multivariate logistic regression model. Variables that retained independent significance were retained and weighted according to their beta coefficients, then rounded to integer values to create a clinically usable score.

The score was externally validated in an independent cohort of 116 patients (68 RCVS, 48 comparators) from two additional international centers. Performance was consistent across derivation and validation cohorts, supporting the generalizability of the tool.

Score Components and Weighting

The RCVS₂ score is composed of five variables, each assigned a point value reflecting its independent contribution to distinguishing RCVS from other vasculopathies. The acronym RCVS₂ encodes the five variables:

Variable	Criterion	Points
R — Recurrent or single thunderclap headache	Recurrent thunderclap headache (two or more TCH episodes)	+3
C — Carotid artery involvement	Intracranial internal carotid artery involvement on vascular imaging	−2
V — Vasoconstrictive trigger	Identifiable vasoconstrictive drug use or postpartum state within 4 weeks	+3
S — Sex (female)	Female biological sex	+1
S — Subarachnoid hemorrhage	Convexal (non-aneurysmal) subarachnoid hemorrhage on CT or MRI	+1

Score range: −2 to +10

Interpretation Thresholds

RCVS2 Score	Interpretation	Performance
> 5	High probability of RCVS	Sensitivity ~90%, Specificity ~99%, LR+ ~86
2 to 5	Indeterminate; further evaluation required	Cannot reliably distinguish RCVS from PACNS
≤ 1	RCVS less likely; consider alternative diagnoses	High negative predictive value for RCVS

Detailed Variable Analysis

R: Recurrent Thunderclap Headache (+3 points)

Recurrent TCH is the single most discriminating feature favoring RCVS. In the derivation cohort, 80% of RCVS patients reported two or more distinct TCH episodes versus fewer than 10% of PACNS patients. The recurrent, stereotyped, and often trigger-provokable nature of RCVS headaches reflects the episodic instability of cerebrovascular tone rather than fixed inflammatory or anatomic pathology.

For scoring purposes, "recurrent" requires at least two independently occurring thunderclap headaches (reaching maximal intensity within 60 seconds). TCH episodes that represent pain fluctuations within a single continuous headache do not fulfill this criterion. The first episode is commonly the most severe; subsequent episodes may be slightly less intense but are recognizable as the same type of pain.

A single TCH episode (rather than recurrent) still occurs in RCVS (typically early in the course) and scores 0 for the R variable. However, clinicians evaluating a patient days to weeks into their illness may be capturing the recurrent phase; serial assessment is therefore important.

C: Carotid Artery Involvement (−2 points)

The only negatively weighted variable, intracranial internal carotid artery (ICA) involvement on vascular imaging argues against RCVS and toward an alternative diagnosis. Vasoconstriction in RCVS characteristically begins in the distal cortical and small branches and progresses centripetally; involvement of the large proximal arteries including the intracranial ICA is a late and uncommon finding in RCVS but is more frequently seen in PACNS and other large-vessel vasculopathies.

The intracranial ICA includes the cavernous, clinoid, ophthalmic, communicating, and choroidal segments (C3 through C7 in the Bouthillier classification). Involvement may manifest as segmental stenosis, irregularity, or "beading" on MR angiography (MRA), CT angiography (CTA), or digital subtraction angiography (DSA). Isolated involvement of the MCA, ACA, or PCA without ICA disease does not score this variable.

The rationale for the negative weight reflects the pathophysiology of RCVS: the distal-to-proximal centripetal pattern rarely reaches the ICA except in severe or prolonged cases. When the ICA is involved early, an inflammatory (PACNS), atherosclerotic, or dissection etiology should be prioritized.

V: Vasoconstrictive Trigger (+3 points)

The identification of a vasoconstrictive trigger carries equal weight to recurrent TCH, reflecting the powerful epidemiological and pathophysiological link between RCVS and exogenous vasoactive exposures. A trigger is defined as use of a recognized vasoconstrictive substance or the postpartum state within four weeks of symptom onset.

Recognized vasoconstrictive triggers for scoring purposes include:

• Triptans (sumatriptan, rizatriptan, eletriptan, and others)
• Ergot alkaloids (ergotamine, dihydroergotamine, methysergide)
• Serotonergic antidepressants (SSRIs, SNRIs) at the time of initiation or dose change
• Sympathomimetic nasal decongestants (pseudoephedrine, oxymetazoline)
• Illicit vasoactive substances: cocaine, amphetamines, MDMA, cannabis (especially high-potency)
• Postpartum state: delivery within four weeks, particularly with pre-eclampsia, oxytocin, ergometrine, or bromocriptine use
• Tacrolimus and cyclosporine in transplant recipients
• Bevacizumab and other anti-VEGF agents

Patients must be carefully and systematically asked about all drug exposures, including over-the-counter preparations, herbal supplements, recreational substances, and medications prescribed for non-neurological conditions. Patients may not spontaneously volunteer use of recreational drugs or associate their medications with headache.

S: Sex — Female (+1 point)

Female sex adds one point to the RCVS₂ score, reflecting the consistent epidemiological observation that RCVS disproportionately affects women. While RCVS does occur in men, the female predominance (3:1 to 4:1 in most series) likely reflects hormonal influences on cerebrovascular regulation, the specific postpartum trigger, and possibly a greater susceptibility to serotonin-mediated vasomotor dysregulation.

The relatively modest weight of this variable (+1) acknowledges that sex alone has limited discriminating power and that RCVS in men is well documented, particularly in the context of drug exposure or strenuous physical exertion.

S: Subarachnoid Hemorrhage — Convexal (+1 point)

Non-aneurysmal convexal subarachnoid hemorrhage (cSAH) is a recognized complication and supportive finding in RCVS. Blood is distributed in the sulci overlying the cerebral convexities (as opposed to the basal cisterns in aneurysmal SAH) due to rupture of small cortical surface vessels subject to intense vasoconstriction and reperfusion injury. On CT, cSAH appears as hyperdensity in one or a few cortical sulci; on FLAIR MRI, sulcal hyperintensity is seen (though susceptibility-weighted imaging or gradient echo is more sensitive for small hemorrhages).

cSAH was present in approximately 30% of RCVS cases in the derivation cohort and is distinctly less common in PACNS (where parenchymal microbleeds or leptomeningeal enhancement without hemorrhage are more typical). The presence of cSAH in a patient with thunderclap headache should therefore raise RCVS prominently in the differential, while also prompting urgent exclusion of aneurysmal SAH (which requires basal cistern hemorrhage on CT or xanthochromia on lumbar puncture).

Primary Differential Diagnosis: PACNS

Why the Distinction Matters

Primary angiitis of the central nervous system (PACNS) is a rare, inflammatory vasculopathy confined to the CNS, characterized by granulomatous or lymphocytic infiltration of medium and small vessels. Unlike RCVS, PACNS is a progressive disease that, untreated, leads to permanent neurological disability or death from recurrent strokes and encephalopathy. Standard treatment involves high-dose corticosteroids (methylprednisolone 1 g/day for 3 to 5 days, then prednisone 1 mg/kg/day) combined with cyclophosphamide, typically continued for 12 to 18 months.

Administering these agents to a patient with RCVS carries significant risk: cyclophosphamide is gonadotoxic, immunosuppressive, and associated with hemorrhagic cystitis and secondary malignancies. Corticosteroids have been associated with a paradoxically worse course in RCVS in some observational series, possibly by promoting rebound vasospasm upon taper.

Clinical and Imaging Distinctions

Feature	RCVS	PACNS
Headache	Recurrent thunderclap; severe; resolves within days to weeks	Insidious, progressive; rarely thunderclap
Age and sex	Women, 4th–5th decade	Males slightly predominant; broader age range
Triggers	Drugs, postpartum, exertion	None identified
CSF	Normal or mildly abnormal (protein <100 mg/dL, WBC <10/mm³)	Often abnormal: elevated protein, lymphocytic pleocytosis
Angiographic pattern	Distal predominant; multifocal; centripetal progression; resolves in 12 weeks	Diffuse; random; proximal and distal; may involve ICA; does not resolve spontaneously
Vessel wall MRI	No mural enhancement (or minimal)	Concentric mural enhancement in inflamed vessels
Parenchymal lesions	Watershed infarcts (late); PRES; convexal SAH	Multiple infarcts in different territories; microbleeds; leptomeningeal enhancement
Brain biopsy	Normal or non-specific changes	Granulomatous or lymphocytic vasculitis
Outcome	Self-limited; resolves in 1–3 months	Progressive without treatment; high morbidity

Diagnostic Workup

Initial Evaluation

Any patient presenting with thunderclap headache requires immediate evaluation to exclude life-threatening causes before RCVS is entertained:

1. Non-contrast CT head: Identifies aneurysmal SAH (>95% sensitivity within 6 hours of ictus), intracerebral hemorrhage, and convexal SAH. A normal CT does not exclude SAH beyond the 6-hour window.
2. Lumbar puncture: Mandatory if CT is negative and clinical suspicion for SAH is high, particularly for headaches occurring more than 6 hours prior to presentation. Xanthochromia or elevated red blood cells in the final tube (corrected for traumatic tap) indicate SAH. Cerebrospinal fluid analysis also assesses for meningitis, encephalitis, and PACNS (where pleocytosis and elevated protein are expected).
3. MRI brain with DWI: Evaluates for ischemic stroke, PRES (FLAIR hyperintensity in posterior cortical/subcortical regions), cortical spreading depression, and leptomeningeal enhancement (suggesting PACNS or infectious meningitis).
4. MR angiography or CT angiography: The initial vascular imaging study of choice. Identifies multifocal cerebral artery vasoconstriction, but may be normal early in RCVS (first 24 to 72 hours) due to distal vessel involvement below MRA resolution. A normal MRA or CTA does not exclude RCVS.

Advanced Imaging

When initial non-invasive vascular imaging is negative or inconclusive, further studies are guided by clinical probability:

• Digital subtraction angiography (DSA): The gold standard for detecting cerebral vasoconstriction, with superior resolution for distal vessels compared to MRA or CTA. However, DSA itself can transiently worsen vasospasm and carries procedural risk. In practice, DSA is reserved for cases where non-invasive imaging is negative but clinical suspicion is high, or when brain biopsy is planned (for possible PACNS).
• High-resolution vessel wall MRI (VW-MRI): Increasingly used to differentiate RCVS from inflammatory vasculopathies. In PACNS, concentric mural enhancement of affected vessel walls (post-gadolinium T1-weighted imaging) reflects active inflammation. RCVS typically shows no or minimal mural enhancement. VW-MRI can detect vessel wall abnormalities in vessels that appear normal on standard MRA, and is now considered a key tool in the RCVS vs. PACNS workup at specialized centers.
• Transcranial Doppler (TCD): Mean flow velocities in the MCA above 120 to 140 cm/s are consistent with vasospasm and can be used serially to track the evolution of vasoconstriction non-invasively. TCD is limited to large proximal vessels and cannot assess distal convexal branches.
• Perfusion imaging (CT perfusion or MR perfusion): Identifies hemodynamically significant ischemia in at-risk territories, guiding the urgency of intervention and monitoring during the acute phase.

Laboratory Evaluation

Laboratory testing aims to identify systemic inflammatory disease, infection, and metabolic triggers:

• Complete blood count, metabolic panel, coagulation studies
• Erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP): typically normal in RCVS; elevated in PACNS and systemic vasculitis
• Antinuclear antibody (ANA), ANCA (anti-MPO, anti-PR3), anti-dsDNA, complement levels: to exclude systemic lupus erythematosus-related CNS vasculitis and ANCA-associated vasculitis
• Antiphospholipid antibodies: relevant in the postpartum period and in patients with prior thrombosis
• HIV, syphilis (VDRL/RPR), Lyme serology: infectious vasculitis mimics
• Urine drug screen: essential to identify vasoconstrictive substance use
• Serum calcium, PTH: hypercalcemia as a RCVS trigger
• Urine or plasma catecholamines/metanephrines: pheochromocytoma evaluation in recurrent or severe cases

Brain and Leptomeningeal Biopsy

Brain biopsy (targeted to an abnormal area or non-dominant frontal lobe tip leptomeningeal biopsy) is the definitive diagnostic test for PACNS, showing granulomatous or lymphocytic vasculitis on histopathology. Biopsy is not routinely required for RCVS diagnosis and carries a 0.5 to 2% serious complication rate. Indications include:

• Diagnostic uncertainty persisting after complete non-invasive workup
• Low RCVS₂ score (≤2) with progressive neurological decline
• Abnormal vessel wall MRI suggesting active inflammation
• CSF pleocytosis or elevated protein inconsistent with RCVS
• Failure of spontaneous vascular normalization beyond 12 weeks

Management Principles

Trigger Elimination

Immediate discontinuation of all vasoconstrictive drugs is the most important therapeutic intervention in RCVS. This includes stopping triptans, ergot derivatives, SSRIs and SNRIs (if recently started or dose-changed), decongestants, and recreational substances. In postpartum RCVS, bromocriptine (if used for lactation suppression) should be discontinued, and methylergonovine (if prescribed for uterine involution) is absolutely contraindicated.

Acute Headache Management

Acute pain relief is challenging because triptans and ergotamines (the most effective acute migraine treatments) are contraindicated. Accepted options include intravenous opioids (with caution due to potential hemodynamic effects), intravenous magnesium sulfate (which has mild vasodilatory properties and is particularly favored in postpartum RCVS), indomethacin, and short-course oral verapamil or nimodipine for headache prophylaxis during the acute phase. Nimodipine and verapamil are the most widely used agents for prophylaxis, though evidence from randomized trials is lacking and their efficacy for preventing neurological complications (as opposed to headache) is unproven.

Blood Pressure Management

Hypertension, whether pre-existing or reactive to pain and anxiety, may worsen vasospasm and promote PRES. Blood pressure should be maintained below 160/100 mmHg in the acute phase, using labetalol, nicardipine, or hydralazine. Sodium nitroprusside is avoided due to theoretical risk of cerebrovascular steal.

Avoidance of Corticosteroids

Corticosteroids are not indicated for RCVS and may be harmful. Several observational studies have reported higher rates of neurological worsening, stroke, and prolonged vasospasm in RCVS patients treated with corticosteroids, potentially due to paradoxical rebound vasoconstriction. This reinforces the critical importance of accurately distinguishing RCVS from PACNS before initiating immunosuppression.

Monitoring and Follow-up

Patients with RCVS complicated by stroke, PRES, or significant hemorrhage require ICU-level monitoring during the acute phase. Serial neurological examination and transcranial Doppler or repeated vascular imaging are used to track the evolution of vasoconstriction. For uncomplicated RCVS, outpatient management with strict trigger avoidance and clinical follow-up is appropriate. Repeat MRA at 4 to 12 weeks is recommended to document vascular normalization, which is required to confirm the diagnosis of RCVS retrospectively (per the 2007 Calabrese diagnostic criteria).

Special Populations

Postpartum RCVS

Postpartum RCVS is the most common clinical subtype and warrants special attention. It typically occurs in the first week after delivery and is strongly associated with preeclampsia/eclampsia, uterotonic agents (oxytocin, methylergonovine, carboprost), and bromocriptine. The clinical presentation may overlap significantly with hypertensive disorders of pregnancy and eclampsia-associated PRES, and these conditions may coexist.

Management priorities in postpartum RCVS include: discontinuation of all vasoactive uterotonic agents, intravenous magnesium sulfate (a standard eclampsia treatment that also has mild cerebrovascular vasodilatory effects), aggressive blood pressure control, and avoidance of ergot alkaloids in any form.

Pediatric RCVS

RCVS in children presents similarly to adults, though drug exposure is a less common trigger and spontaneous or post-infectious RCVS is more common. The RCVS₂ score has not been formally validated in pediatric populations, and its performance in children (particularly the sex variable and vasoconstrictive trigger criterion) may differ.

RCVS in Older Adults

In patients over 60, the differential diagnosis of RCVS broadens to include cerebral amyloid angiopathy-related inflammation (CAA-ri), which can present with convexal SAH and cognitive change but is distinguished by microbleeds, cortical superficial siderosis, white matter changes on MRI, and absence of TCH. Medication-related RCVS in older adults most commonly involves triptans (for chronic migraine), SSRIs, and pseudoephedrine-containing cold remedies.

Prognosis

The overall prognosis of RCVS is favorable. In most patients, headaches resolve within three to four weeks and vascular abnormalities normalize within 12 weeks. Long-term neurological outcomes are excellent for uncomplicated cases. However:

• 10 to 15% of patients develop ischemic stroke, PRES, or significant hemorrhage, which may cause permanent deficits.
• Recurrence of RCVS is uncommon (estimated 5 to 8% over 5 to 10 years) but is more likely with ongoing exposure to vasoconstrictive triggers.
• Patients with PRES generally recover fully if blood pressure is controlled and triggers are eliminated, though posterior cortical infarcts can occur in the context of severe PRES.
• Patients who experience ischemic stroke have outcomes determined by stroke size, location, and time to treatment, similar to stroke from other etiologies.

Limitations of the RCVS₂ Score

The RCVS₂ score is a validated and high-performing diagnostic tool, but the following limitations apply:

• Retrospective variable assessment: Some variables, particularly the recurrent TCH criterion, may not be assessable at initial presentation if the patient presents after a single headache episode. Serial reassessment as the clinical course evolves increases score accuracy.
• Imaging-dependent variables: The carotid artery involvement (C) and convexal SAH (S) variables require vascular imaging and neuroimaging, which may not yet be available at initial scoring. Scores should be updated as imaging results return.
• Normal vascular imaging in early RCVS: Vascular imaging is negative in up to 30% of RCVS patients during the first 24 to 72 hours (due to distal vessel involvement below MRA resolution). A negative MRA in the presence of a high clinical score should not rule out RCVS; repeat imaging at 5 to 7 days is indicated.
• Score does not differentiate RCVS subtypes: The RCVS₂ score does not predict severity, likelihood of complications, or specific triggers. Clinical management must be individualized.
• Comparator population was predominantly PACNS: The derivation cohort used PACNS as the primary comparator. The score may perform differently against other RCVS mimics (e.g., intracranial atherosclerosis, reversible posterior leukoencephalopathy, CNS infections, or moyamoya disease).
• Not validated in pediatric populations: See Pediatric RCVS section above.
• This calculator is for educational use only. Clinical diagnosis and management decisions must involve a neurologist or neurovascular specialist with access to the full clinical history, examination, and imaging data.