12-phase flow (12)

1. 1FRAME
   Frame the encounter as a TWO-CHANNEL acute-vestibular-syndrome problem: positively diagnose PERIPHERAL AVS (vestibular neuritis / labyrinthitis) AND robustly exclude the can't-miss central mimic (~25% of AVS is posterior-circulation/AICA stroke). The peripheral-vs-central HINTS decision is the spine of this engine. Definitive stroke/SSNHL/Ménière/migraine/falls management is routed OUT by engine_id, not re-authored.
   advance: two-channel AVS scope confirmed; out-of-scope definitive management flagged for engine_id routing
2. 2ENTRY
   Apply the TiTrATE timing pivot at the door: CONTINUOUS sustained spontaneous vertigo ≥24 h with nystagmus = AVS → this engine's HINTS channel; brief recurrent position-triggered (<1 min, fatiguing) spells = triggered-episodic → route to ent.bppv.core.v1 (Dix-Hallpike, NOT HINTS). Timing/trigger is captured first because it determines which bedside exam is even valid (Newman-Toker Neurol Clin 2015; Bárány AUVP 2022).
   inputs: symptom_timing_continuous_vs_episodic, spontaneous_vs_triggered_onset
   actions: workup.vertigo
   advance: TiTrATE category = AVS (continuous spontaneous) confirmed; triggered-episodic redirected to ent.bppv.core.v1
3. 3CONTEXT
   Build the pre-test peripheral-vs-central prior: spontaneous unidirectional fixation-suppressed nystagmus (peripheral) vs direction-changing/vertical (central); new auditory symptoms (labyrinthitis / AICA / SSNHL — route by engine_id); vascular risk factors (raise central prior); viral prodrome (post-viral hypothesis, frames the corticosteroid debate); age (vascular + compensation + fall-risk modifier). This phase sets the Bayesian prior before HINTS.
   inputs: nystagmus_character_unidirectional_vs_direction_changing, acute_hearing_loss_tinnitus, vascular_risk_factors, recent_viral_prodrome, age
   actions: workup.vertigo
   advance: peripheral-vs-central pre-test prior assigned; auditory/vascular/viral modifiers captured
4. 4RED_FLAGS
   Perform HINTS (Head-Impulse–Nystagmus–Test-of-Skew) + screen the 4 D's / gait / focal signs in EVERY continuous AVS. Dangerous (central, "INFARCT") pattern = NORMAL head-impulse, OR direction-CHANGING / vertical nystagmus, OR skew (ANY one) → posterior-circulation stroke until excluded → route OUT to neuro.posterior-circulation-stroke.core.v1. HINTS out-performs early MRI-DWI and ABCD2. Critical guardrail: HINTS is valid ONLY in continuous AVS with nystagmus — NEVER apply it to triggered-episodic vertigo (Kattah Stroke 2009; Newman-Toker AEM 2013; Saber Tehrani Neurology 2014).
   inputs: hints_head_impulse, hints_nystagmus_direction, hints_test_of_skew, central_neuro_4Ds_gait
   actions: calc.abcd2, calc.nihss, protocol.stroke, workup.acute_stroke, workup.acute_headache
   advance: HINTS interpreted (central pattern routed OUT by engine_id) AND 4 D's/gait/focal screen complete
5. 5INITIAL_WORKUP
   For the peripheral channel (continuous AVS, ALL-peripheral HINTS = abnormal head-impulse + unidirectional fixation-suppressed nystagmus + no skew, no central signs, no acute hearing loss): vestibular neuritis is a CLINICAL diagnosis (Bárány AUVP criteria) — routine imaging and lab panels are NOT required when criteria are met. CBC/CMP/inflammatory markers only if systemic/infective concern (febrile, immunocompromised, suspected suppurative/infectious labyrinthitis) or to gate corticosteroid use (glucose). Audiometry distinguishes neuritis (normal hearing) from labyrinthitis (SNHL → SSNHL pathway).
   inputs: nystagmus_character_unidirectional_vs_direction_changing
   actions: workup.vertigo, panel.cbc, panel.cmp, panel.inflammation
   advance: all-peripheral HINTS + clinical AUVP criteria met (imaging deferred), OR systemic/atypical features trigger labs/imaging
6. 6BRANCHING_WORKUP
   If HINTS is central / cannot be applied (no nystagmus, uncooperative) / red flags present / high vascular risk → MRI-DWI + posterior-circulation-stroke pathway, recognising a single early DWI is falsely negative in ~12-15% (~50% small strokes) so a negative early scan does NOT exclude stroke when HINTS is central — delayed MRI / specialist if needed (route OUT). If acute SNHL accompanies AVS (labyrinthitis) → audiometry + route to ent.sudden-sensorineural-hearing-loss.core.v1 (time-critical steroid window). If recurrent positional spells emerge after the acute phase → post-neuritis secondary BPPV → route to ent.bppv.core.v1.
   inputs: mri_dwi_posterior_fossa, acute_hearing_loss_tinnitus
   actions: workup.acute_stroke, workup.vertigo
   advance: central pattern imaged/routed OUT, OR labyrinthitis routed to SSNHL, OR peripheral-isolated AVS confirmed for treatment
7. 7DIFFERENTIAL
   Terminal vestibular differential with named pivots: vestibular neuritis (continuous AVS, unidirectional fixation-suppressed nystagmus, ABNORMAL head-impulse, NO skew, NO central signs, NO hearing loss) vs labyrinthitis (same + acute SNHL → ent.sudden-sensorineural-hearing-loss.core.v1) vs posterior-circulation/AICA stroke (NORMAL head-impulse OR direction-changing/vertical nystagmus OR skew OR 4 D's — route to neuro.posterior-circulation-stroke.core.v1) vs BPPV (triggered-episodic <1 min, positional, fatiguing canal-specific nystagmus — route to ent.bppv.core.v1) vs Ménière (recurrent spontaneous spells minutes-hours + fluctuating low-frequency SNHL/fullness — route to ent.meniere-disease.core.v1) vs vestibular migraine (episodic spontaneous + migraine features — route to neuro.vestibular-migraine.core.v1). The decisive pivot = HINTS + continuous-vs-episodic + hearing.
   actions: workup.vertigo
   advance: single best vestibular diagnosis selected; out-of-scope diagnoses routed by engine_id; co-existence (post-neuritis BPPV) flagged
8. 8RISK_STRATIFICATION
   For confirmed peripheral AVS: stratify fall/injury risk (age, gait/balance impairment, anticoagulation, osteoporosis, no home support), dehydration severity (intractable vomiting), and central re-screen if any equivocal feature. For an unwell/systemic picture (suspected infective labyrinthitis, meningitis-associated): NEWS2 / qSOFA to detect a non-vestibular systemic cause needing a different pathway. The ABCD2 caveat: ABCD2 UNDER-performs HINTS — do NOT use ABCD2 to "rule out" stroke in AVS.
   inputs: age, vascular_risk_factors, intractable_vomiting_dehydration
   actions: calc.abcd2, calc.nihss, calc.qsofa, calc.news2
   advance: fall-risk / dehydration / systemic-screen stratified; ABCD2-as-rule-out guardrail enforced
9. 9TREATMENT
   Three-lever peripheral-AVS management: (1) SHORT-COURSE vestibular suppressant + antiemetic for the acute symptomatic phase ONLY, strictly ≤48-72 h — prolonged use RETARDS central compensation (the core caveat); (2) EARLY vestibular rehabilitation begun once acute vomiting settles — the single evidence-based recovery lever (McDonnell Cochrane 2015 — dizziness OR 2.67, DHI SMD −0.83); (3) the DEBATED corticosteroid step — methylprednisolone improves CALORIC recovery (Strupp NEJM 2004, 62.4 vs 39.6 pp) but Cochrane (Fishman 2011) / Leong OHNS 2021 find NO symptomatic/long-term benefit and "insufficient evidence" — present as shared-decision equipoise, weigh diabetes/immunocompromise/pregnancy. ANTIVIRALS are NOT recommended (Strupp NEJM 2004 — valacyclovir ineffective). Acute SNHL (labyrinthitis) → route to ent.sudden-sensorineural-hearing-loss.core.v1 (its own time-critical steroid pathway).
   inputs: pregnancy, diabetes_or_immunocompromise, recent_viral_prodrome
   advance: short-course suppressant time-limited (≤48-72 h); early vestibular rehab initiated; corticosteroid shared-decision documented; antivirals withheld
10. 10DISPOSITION
    All-peripheral HINTS + safe gait + tolerating oral intake → discharge with early vestibular-rehab plan, suppressant-stop instruction, and central return precautions. Central HINTS / 4 D's / cannot apply HINTS / acute hearing loss → admit / emergent neuro / route OUT (neuro.posterior-circulation-stroke.core.v1 or ent.sudden-sensorineural-hearing-loss.core.v1). Intractable vomiting/dehydration or unsafe gait/high fall risk (frail elderly, no support) → short-stay/admit for IV rehydration + supervised mobilisation + PT.
    inputs: central_neuro_4Ds_gait, intractable_vomiting_dehydration, age
    actions: protocol.stroke
    advance: disposition documented; central/SNHL cases routed OUT by engine_id; fall-risk/hydration disposition set
11. 11MONITORING
    Re-examine within the first 24-72 h: peripheral AVS should show GRADUAL improvement (nystagmus decreasing, gait improving) as central compensation begins. NON-resolution, worsening, NEW neuro/auditory features, or evolving direction-changing nystagmus → re-triage as CENTRAL (small posterior-fossa strokes are missed on early MRI-DWI ~50% — Saber Tehrani Neurology 2014); image / route OUT. STOP the short-course suppressant by 48-72 h regardless; persisting symptomatic suppressant use is itself a compensation-retarding error.
    inputs: nystagmus_character_unidirectional_vs_direction_changing, central_neuro_4Ds_gait
    actions: workup.vertigo
    advance: gradual peripheral recovery confirmed OR re-triaged central; short-course suppressant stopped by 48-72 h
12. 12FOLLOWUP
    Reassess at ~1-4 weeks: most recover via central compensation over weeks; persistent imbalance/oscillopsia → structured vestibular rehabilitation (clinician- or home-based — McDonnell Cochrane 2015). Pursue secondary substrate: post-neuritis BPPV (utricular otoconia shed → new positional spells → route to ent.bppv.core.v1), incomplete compensation in the elderly (fall-injury risk → route to geriatrics.falls.core.v1), and audiometry follow-up if labyrinthitis. Educate on recovery trajectory, that residual unsteadiness for weeks is expected and NOT failure, and central return precautions.
    inputs: age, post_viral_or_post_neuritis_recurrent
    actions: workup.falls
    advance: 1-4 week reassessment booked; vestibular-rehab + secondary-substrate plan documented; falls/BPPV/audiometry referral made if criteria met