12-phase flow (12)

1. 1FRAME
   Frame as a Sarcoptes scabiei infestation with an IMMUNOLOGIC (delayed type-IV) itch that lags infestation by weeks — so itch timing, post-scabetic persistence, and "the whole household + the environment, not just the patient" define management. The great-imitator trap (missed as steroid-worsened eczema) and the classic-vs-crusted split (hyperinfestation, outbreak, sepsis) are set here.
   advance: scabies frame set; classic-vs-crusted + great-imitator + contact/public-health escape routes noted
2. 2ENTRY
   Recognise intense nocturnally-worse generalised pruritus with web-space/genital burrows, the affected-contacts/institutional entry, the crusted-host entry, or the steroid-refractory-eczema great-imitator entry; capture the itch pattern + onset-lag up front.
   inputs: itch_pattern_and_timing
   actions: workup.chronic_pruritus
   advance: entry trigger present; itch pattern + timing recorded
3. 3CONTEXT
   Build the diagnostic + public-health context: classic distribution and burrows (IACS lesion criteria), affected close/household/sexual contacts and institutional residence (the strongest contextual prior + the contact-tracing trigger), and immunocompromise / elderly / neurologic status (crusted-scabies + outbreak risk).
   inputs: lesion_distribution_and_burrows, close_contact_and_institutional_context, immunocompromise_or_crusted_risk
   actions: workup.chronic_pruritus
   advance: IACS clinical level supportable; contact + crusted-risk context established
4. 4RED_FLAGS
   Secondary bacterial infection (honey-crust / pustules / impetiginisation → S. aureus / S. pyogenes) — in crusted scabies a sepsis/bacteraemia source; in endemic settings carries post-streptococcal glomerulonephritis / rheumatic-fever sequelae. Crusted scabies itself is a transmissibility + morbidity red flag (isolation + outbreak control). Institutional cluster → public-health notification.
   inputs: secondary_bacterial_infection_signs, inflammatory_markers
   actions: panel.cbc, panel.inflammation
   advance: impetiginisation / crusted-sepsis / outbreak screened and escalated/notified if present
5. 5INITIAL_WORKUP
   Scabies is largely a clinical diagnosis under the 2020 IACS criteria. Targeted confirmation: dermoscopy ("delta-wing-jet"/burrow sign — high yield, non-invasive), skin-scraping or burrow-ink microscopy (specific but insensitive in classic disease — high mite load makes crusted scabies easy to confirm), biopsy if atypical/CTCL-mimic in the immunocompromised. CBC for eosinophilia/IgE (crusted) and to screen secondary sepsis.
   inputs: dermoscopy_or_microscopy_confirmation, cbc_eosinophilia
   actions: panel.cbc, panel.lft
   advance: IACS certainty level assigned (confirmed/clinical/suspected); confirmatory test done if indicated
6. 6BRANCHING_WORKUP
   Pruritic-dermatosis decision tree: burrows + web-space + affected contacts + nocturnal itch + no atopy → scabies; flexural + atopic diathesis + no burrows/contacts and improves on steroids → atopic dermatitis (route derm.atopic-dermatitis.core.v1 — the dominant misdiagnosis); geometric/exposure-mapped → contact dermatitis (route derm.contact-dermatitis.core.v1); new-drug-linked widespread pruritus → drug eruption (route derm.drug-eruption.core.v1); grouped vesicles + gluten/IgA → dermatitis herpetiformis; grouped excoriated papules without burrows → papular urticaria/insect bites; nits/lice → pediculosis; hyperkeratotic mimic in HIV → exclude CTCL/crusted overlap by biopsy.
   inputs: steroid_refractory_treatment_resistant_eczema
   actions: workup.chronic_pruritus
   advance: scabies confirmed/clinically assigned OR an alternative dermatosis assigned + routed by engine_id
7. 7DIFFERENTIAL
   Terminal pruritic differential with named pivots: scabies vs atopic dermatitis (burrows + web-space + affected contacts + nocturnal itch + worsens-on-steroids pivot — route derm.atopic-dermatitis.core.v1) vs contact dermatitis (geometric/exposure-mapped pivot — route derm.contact-dermatitis.core.v1) vs dermatitis herpetiformis (grouped vesicles + extensor + IgA/gluten pivot) vs papular urticaria/insect bites (grouped urticarial papules, no burrows pivot) vs prurigo nodularis (chronic isolated nodules pivot) vs pediculosis (nits/lice pivot) vs asteatotic/xerotic eczema (dry crazy-paving, elderly winter pivot) vs cutaneous T-cell lymphoma (fixed poikilodermatous, crusted-mimic in immunocompromised — biopsy pivot) vs drug eruption (new-drug timeline pivot — route derm.drug-eruption.core.v1).
   advance: single best diagnosis selected; great-imitator (eczema) actively excluded; crusted-vs-CTCL biopsied in the immunocompromised mimic
8. 8RISK_STRATIFICATION
   Stratify classic vs crusted (Norwegian) and grade severity: classic (~10-15 mites, outpatient) vs crusted Grade 1/2/3 (Hasan distribution/crust/recurrence grading — schema-blocked, narrated) which scales the ivermectin dose count (3/5/7), the isolation intensity, and the outbreak-control footprint. Layer secondary-sepsis risk, immunocompromise depth, and institutional-cluster scale.
   inputs: crusted_scabies_severity_grade, immunocompromise_or_crusted_risk
   advance: classic-vs-crusted + crusted grade + sepsis/outbreak modifier assigned
9. 9TREATMENT
   TREAT THE PATIENT + ALL CONTACTS + THE ENVIRONMENT, never the patient alone. Classic: permethrin 5% whole-body neck-down (scalp/face also in infants/elderly/crusted), wash off 8-14 h, REPEAT day 7-14; or oral ivermectin 200 mcg/kg day 1 + day 8 (preferred for outbreaks/when topical impractical). Alternatives: benzyl benzoate, precipitated sulfur (pregnancy/neonatal-safe <2 mo), crotamiton (lower efficacy). Crusted scabies: combined multi-dose oral ivermectin (Grade 1/2/3 → 3/5/7 doses, e.g. d1,2,8,9,15±22,29) + daily topical scabicide + keratolytic + strict isolation + environmental decontamination. Adjuncts: simultaneous contact treatment (2-month look-back), environmental decontamination (hot-wash/hot-dry/seal-bag 72 h), anti-staphylococcal cover if impetiginised (with post-streptococcal-sequelae vigilance in endemic settings), and explicit POST-SCABETIC-ITCH management with topical steroid/antihistamine — counselled as expected, NOT failure. Gating: pregnancy/lactation → permethrin or sulfur; <2 mo or <15 kg → sulfur (avoid ivermectin); crusted → isolate + barrier; do NOT treat as eczema with steroids alone.
   inputs: pregnancy_lactation, age_and_weight, household_and_sexual_contacts_for_treatment, creatinine
   advance: scabicide + repeat dose + simultaneous contact treatment + environmental decontamination + post-scabetic-itch counselling all defined; crusted regimen intensified if applicable
10. 10DISPOSITION
    Classic scabies is outpatient: treat, contact-trace, decontaminate, counsel post-scabetic itch, 2- and 4-week recheck. Crusted scabies / secondary sepsis / institutional outbreak → inpatient isolation (barrier nursing) with combined regimen and route secondary sepsis OUT to the systemic-infection pathway; institutional/endemic cluster → public-health notification + mass drug administration consideration (cohort treatment of the whole facility/community).
    inputs: endemic_or_resource_limited_setting, secondary_bacterial_infection_signs
    advance: disposition documented; crusted/outbreak admitted+isolated+notified; classic discharged with full contact+environment plan
11. 11MONITORING
    Set itch-trajectory expectations BEFORE discharge: post-scabetic pruritus may persist 2-4 wk after successful eradication and is NOT failure — manage with emollient/topical steroid/antihistamine, do not re-treat reflexively. Reassess at 2 and 4 wk. Apparent failure → structured workup: (1) re-infestation from an untreated contact (commonest), (2) non-adherence/mis-application, (3) post-scabetic itch misread, (4) wrong diagnosis, then (5) true persistence/resistance (rising over time per the 2024 meta-analysis) — escalate dose/agent only after 1-4 excluded.
    inputs: prior_scabicide_adequacy_and_adherence
    actions: workup.chronic_pruritus
    advance: itch-trajectory counselled; 2/4-wk recheck booked; failure workup structured before any re-treatment
12. 12FOLLOWUP
    Confirm eradication at ~4 wk; ensure ALL contacts were treated (untreated contacts = the dominant recurrence driver); reinforce environmental decontamination; in endemic/institutional settings arrange surveillance, MDA linkage, and post-streptococcal-sequelae follow-up after secondary impetigo (urinalysis/BP for post-strep GN). Crusted scabies: relapse is common on return to an endemic community — plan repeat-screening and a low threshold to re-treat the index + cohort.
    inputs: endemic_or_resource_limited_setting, household_and_sexual_contacts_for_treatment
    actions: workup.chronic_pruritus
    advance: eradication confirmed; contact + environment completion verified; endemic/crusted surveillance + post-strep-sequelae follow-up arranged