12-phase flow (12)

1. 1FRAME
   Frame the cutaneous drug-eruption SPECTRUM and the central triage question: benign simple morbilliform/exanthematous (~90%) vs life-threatening SCAR. STOP/identify the culprit drug is the universal cornerstone across every branch. SJS/TEN is recognised here and ROUTED to derm.sjs-ten.core.v1 (managed there, not re-authored). Anaphylactic/urticarial drug reactions route to allergy.anaphylaxis.v1 / derm.urticaria.core.v1.
   advance: spectrum + triage frame set; SJS/TEN + anaphylaxis routing-out scope declared
2. 2ENTRY
   Recognise a cutaneous eruption temporally linked to a drug: symmetric morbilliform on a new drug vs the SCAR-feature / SJS-TEN / fixed-drug-eruption / urticarial entries. Capture the drug timeline as the spine of causality.
   advance: drug-linked eruption recognised; entry pattern identified
3. 3CONTEXT
   Build the causality + risk context: complete drug timeline with latency windows (4–14 d morbilliform/SJS-TEN, 2–8 wk DRESS, <4 d AGEP) and ALDEN-style most-probable-culprit logic; prior SCAR/culprit-class exposure; HLA risk allele (B*15:02/B*58:01/A*31:01); HIV/immunocompromise; age (pediatric Mycoplasma/MIRM overlap, geriatric polypharmacy); fever.
   inputs: drug_exposure_timeline, prior_scar_or_culprit_class, hla_risk_allele, hiv_or_immunocompromise, age, temperature
   advance: single most-probable culprit identified via timeline + ALDEN logic; risk context set
4. 4RED_FLAGS
   Screen the morbilliform background for SCAR-transition red flags: ≥2-site mucositis / skin pain / dusky-targetoid / blisters / Nikolsky → SJS/TEN (route derm.sjs-ten.core.v1, workup.sjs_ten, SCORTEN noted). Facial edema + lymphadenopathy + 2–8 wk latency + eosinophilia/organ derangement → DRESS. Urticaria/angio-oedema/airway/hypotension → anaphylactic drug reaction (route workup.anaphylaxis / allergy.anaphylaxis.v1). Any of these = "morbilliform that may be early SCAR" → escalate, do not treat as benign.
   inputs: mucosal_involvement, skin_pain_and_blistering, facial_edema_and_lymphadenopathy, sbp, urticarial_angioedema_features
   actions: workup.sjs_ten, workup.dress, workup.anaphylaxis, panel.inflammation
   advance: SCAR + anaphylaxis red flags screened; SJS/TEN + anaphylaxis routed OUT by engine_id if positive
5. 5INITIAL_WORKUP
   No test confirms benign morbilliform — it is clinical. Targeted SCAR workup: CBC with differential (eosinophilia → DRESS; neutrophilia → AGEP; atypical lymphocytes → DRESS), LFT + creatinine for DRESS visceral involvement, inflammatory markers; skin biopsy when SCAR/atypia suspected (interface dermatitis morbilliform; full-thickness necrosis SJS/TEN; subcorneal pustules AGEP). Compute RegiSCAR score for DRESS; SCORTEN belongs to the SJS/TEN sibling.
   inputs: eosinophil_count, lft, creatinine, wbc_differential
   actions: panel.cbc, panel.lft, panel.renal, workup.abnormal_lft
   advance: SCAR organ-screen labs resulted; biopsy sent if SCAR/atypia; RegiSCAR scored for DRESS
6. 6BRANCHING_WORKUP
   Drug-eruption decision tree: benign symmetric blanching morbilliform, afebrile, no mucosa/organ → simple exanthematous (supportive + surveil). Pustular (dozens sterile non-follicular pustules + neutrophilia, <2 wk, flexural) → AGEP (EuroSCAR score). Facial edema + eosinophilia + 2–8 wk latency + hepatitis/AKI/HHV-6 → DRESS (RegiSCAR; route workup.dress + workup.abnormal_lft). Mucositis + detachment → SJS/TEN (route derm.sjs-ten.core.v1). Recurrent same-site dusky plaque on re-exposure → fixed drug eruption. Transient wheals/angio-oedema → urticarial/anaphylactic (route).
   inputs: pustular_morphology
   actions: workup.dress, workup.sjs_ten, workup.abnormal_lft
   advance: terminal drug-eruption phenotype assigned and routed if SCAR/anaphylaxis
7. 7DIFFERENTIAL
   Terminal differential with named pivots: simple morbilliform/exanthematous (symmetric blanching, afebrile, no mucosa/organ — supportive) vs DRESS (facial edema + eosinophilia + 2–8 wk latency + organ — RegiSCAR pivot) vs SJS/TEN (mucositis + skin pain + detachment + Nikolsky pivot — route) vs AGEP (sterile non-follicular pustules + neutrophilia + rapid pivot) vs fixed drug eruption (recurrent same-site dusky round plaque pivot) vs urticarial/anaphylactic drug reaction (transient wheals + angio-oedema pivot — route) vs viral exanthem (no clear culprit, prodrome, pediatric — drug-timeline pivot) vs acute GVHD/Mycoplasma-induced rash-and-mucositis (pediatric, no drug-timeline pivot).
   inputs: mucosal_involvement, facial_edema_and_lymphadenopathy
   advance: single best phenotype selected; "morbilliform that may be early SCAR" explicitly excluded or escalated
8. 8RISK_STRATIFICATION
   Severity = SCAR-feature burden. Simple morbilliform (no fever/mucosa/organ/eosinophilia) → low risk, outpatient supportive. DRESS by RegiSCAR (possible/probable/definite) + organ-involvement extent → inpatient. SJS/TEN by %BSA detachment + SCORTEN → route derm.sjs-ten.core.v1. AGEP → usually self-limited on withdrawal. Anaphylaxis → emergent. RegiSCAR/SCORTEN/EuroSCAR-AGEP scores are schema-blocked (no registry calculator) — captured narratively + in companion brief.
   inputs: eosinophil_count, lft, creatinine
   advance: phenotype-specific severity tier + disposition intent assigned
9. 9TREATMENT
   STEP 1 (universal, every branch): STOP / identify the culprit drug + all non-essential cross-reactors — the single highest-impact action. STEP 2 benign morbilliform: supportive — emollient, mid-potency topical corticosteroid (triamcinolone), oral antihistamine for itch (cetirizine/hydroxyzine); "treat-through" only in defined low-risk scenarios (essential non-substitutable drug, mild isolated rash, no SCAR features, close monitoring). STEP 3 SCAR-specific: DRESS → systemic corticosteroid (prednisone ~0.5–1 mg/kg/day) with a LONG ~6–12 wk taper ± cyclosporine when steroid-contraindicated; SJS/TEN spectrum → route derm.sjs-ten.core.v1 (cyclosporine/etanercept/IVIG managed there); AGEP → withdrawal ± short topical/short systemic steroid (self-limited). STEP 4: pharmacogenomic prevention + lifelong culprit/cross-reactor avoidance card. Gate on pregnancy/renal/hepatic.
   inputs: pregnancy, creatinine
   advance: culprit stopped (universal); phenotype-appropriate step started; SJS/TEN routed; avoidance documentation begun
10. 10DISPOSITION
    Simple morbilliform → outpatient with explicit SCAR return-precautions (mucosal sores, facial swelling, fever, skin pain, blistering, malaise) + early review. DRESS → admit (organ surveillance, long steroid taper). SJS/TEN → route derm.sjs-ten.core.v1 (burn-unit/ICU there). AGEP → outpatient/short admission per systemic severity. Anaphylactic → ED/observation (route allergy.anaphylaxis.v1). Document the suspected culprit + cross-reactors in the allergy record before discharge.
    inputs: mucosal_involvement, sbp
    advance: disposition documented; SCAR routed OUT; culprit recorded in allergy record
11. 11MONITORING
    Simple morbilliform: clinical re-check 24–72 h for SCAR-transition emergence (delayed eosinophilia/organ involvement can lag the rash). DRESS: serial CBC (eosinophils), LFT, creatinine through the taper; relapse common on steroid wean; HHV-6/CMV reactivation surveillance; watch for late autoimmune sequelae (thyroiditis, type-1 DM) months–years later. AGEP: pustule resolution + desquamation over days. Renal function via calc.ckd_epi_2021 where DRESS-AKI.
    inputs: eosinophil_count, lft, creatinine
    actions: panel.cbc, panel.lft, panel.renal
    advance: no SCAR transition in benign cases; DRESS organ panels trending to resolution through the taper
12. 12FOLLOWUP
    Lifelong culprit + cross-reactor avoidance card and allergy-record entry (highest-yield recurrence-prevention action). Pharmacogenomic counselling/HLA documentation where applicable (B*15:02/B*58:01/A*31:01). DRESS: structured long-term autoimmune-sequelae surveillance (thyroid, glucose) for ≥1–2 years and complete steroid taper. Patient/family education on never re-challenging the culprit class. Allergy/immunology referral for delabelling vs confirmed avoidance and for safe alternative selection.
    inputs: hla_risk_allele, prior_scar_or_culprit_class
    advance: avoidance card + allergy record + (DRESS) sequelae-surveillance plan + pharmacogenomic counselling documented