12-phase flow (12)

1. 1FRAME
   Frame PG as a rapidly progressive, exquisitely painful neutrophilic ulcerative dermatosis that is (a) a DIAGNOSIS OF EXCLUSION confirmed by clinical criteria (Maverakis Delphi / PARACELSUS) with NO confirmatory test — biopsy EXCLUDES mimics, it does not confirm — and (b) governed by PATHERGY: surgical debridement / aggressive surgery enlarges it catastrophically. The dominant error is misdiagnosis as infection and surgical debridement. ~50-70% have an associated systemic disease.
   advance: exclusion-diagnosis + criteria framing set; pathergy / no-debridement rule flagged; associated-disease mandate noted
2. 2ENTRY
   Recognise the rapidly enlarging, disproportionately painful violaceous ulcer (with or without a preceding pustule, pathergy, antibiotic non-response, or peristomal/postsurgical context); capture pain-out-of-proportion up front as the leading discriminator.
   inputs: ulcer_pain_severity
   actions: workup.chronic_pruritus
   advance: entry trigger present; disproportionate pain recorded
3. 3CONTEXT
   Build the criteria + safety context: violaceous undermined border morphology, rapid progression rate, pathergy/trauma localisation (and the explicit no-debridement flag), and a structured associated-systemic-disease inventory (IBD, inflammatory arthritis, haematologic malignancy / IgA gammopathy). Anchor against Maverakis Delphi minor criteria and the PARACELSUS items.
   inputs: ulcer_border_morphology, ulcer_progression_rate, pathergy_or_trauma_localisation, associated_systemic_disease
   actions: workup.le_edema
   advance: criteria features tallied; pathergy/no-debridement flagged; associated-disease context captured
4. 4RED_FLAGS
   Before attributing a non-healing ulcer to PG, EXCLUDE a true necrotising soft-tissue infection (crepitus, gas, fulminant sepsis, genuinely rapidly advancing necrosis) — that is a surgical emergency and routes OUT (id.necrotising-fasciitis.core.v1). Conversely, recognise fulminant / multifocal / systemically toxic PG that mandates admission + IV immunosuppression. The trap: a misdiagnosed PG sent to surgical debridement enlarges (pathergy) — STOP surgery, immunosuppress.
   inputs: necrotising_infection_red_flags, systemic_toxicity_extent_of_disease
   actions: panel.cbc, panel.inflammation
   advance: true necrotising infection excluded/routed; fulminant PG recognised + escalated; pathergy-driven enlargement recognised and surgery halted
5. 5INITIAL_WORKUP
   PG has NO confirmatory test. Workup is for EXCLUSION + associated disease: tissue culture (bacterial/mycobacterial/fungal) to exclude infection; biopsy from the ulcer EDGE to exclude vasculitis/infection/malignancy (a neutrophilic infiltrate is the Maverakis MAJOR criterion but is supportive, NOT diagnostic); CBC; LFT/renal pre-immunosuppression baseline; latent-TB + HBV/HCV if a biologic is anticipated. Edge biopsy is taken cautiously given pathergy.
   inputs: tissue_culture_including_atypicals, edge_biopsy_to_exclude_mimics, cbc_with_differential, lft, infection_screen_tb_hbv_hcv
   actions: panel.cbc, panel.lft, panel.renal
   advance: infection-exclusion cultures + edge biopsy sent; pre-immunosuppression safety labs drawn
6. 6BRANCHING_WORKUP
   Exclusion decision tree: sterile cultures + antibiotic non-response → away from infection; vascular studies (ABI/venous duplex) + workup.le_edema/workup.cvi → exclude arterial/venous ulcer; ANCA / cryoglobulins / antiphospholipid → exclude vasculitis and thrombo-occlusive mimics; biopsy-edge histology → exclude malignancy (SCC/Marjolin) and infection; and the MANDATORY associated-disease workup — colonoscopy/IBD evaluation, SPEP/immunofixation, haematology, inflammatory-arthritis screen. If all mimics excluded and ≥4/8 Maverakis minor criteria met → PG.
   inputs: antibiotic_nonresponse_with_sterile_cultures, anca_cryoglobulin_antiphospholipid, spep_serum_immunofixation
   actions: workup.le_edema
   advance: mimics excluded; criteria threshold met OR an alternative diagnosis assigned + routed; associated-disease workup initiated
7. 7DIFFERENTIAL
   Terminal exclusion differential with named pivots: PG vs infection/cellulitis/necrotising STI (sterile culture + antibiotic non-response + pathergy pivot — route derm.cellulitis.core.v1 / id.necrotising-fasciitis.core.v1) vs venous ulcer (CEAP/stasis pivot — workup.cvi) vs arterial ulcer (ABI pivot) vs vasculitis (ANCA + biopsy pivot — route rheum.vasculitis.core.v1) vs antiphospholipid/calciphylaxis (thrombo-occlusive + calcium-phosphate/biopsy pivot) vs malignancy/Marjolin (chronicity + edge-biopsy pivot) vs factitial ulcer (geometric/access pivot) vs Sweet syndrome (overlapping neutrophilic, plaques>ulcer pivot) vs ecthyma gangrenosum (Pseudomonas/neutropenia pivot) vs cutaneous Crohn (perianal/biopsy granuloma pivot) vs brown-recluse/loxoscelism (bite history pivot) vs Martorell HYTILU (hypertensive ischaemic supramalleolar pivot). PG remains a diagnosis of exclusion.
   advance: mimics actively excluded; PG diagnosed by criteria OR alternative assigned + routed by engine_id
8. 8RISK_STRATIFICATION
   Stratify by extent/tempo: localised/mild (single, limited, slowly progressive) → topical/intralesional ladder; moderate-severe or rapidly progressive/multifocal → systemic corticosteroid or ciclosporin first-line; fulminant / systemically toxic / pathergy-driven enlargement after misdirected surgery → admit + IV immunosuppression + multidisciplinary. Layer the prognostic modifier: associated haematologic malignancy / IgA gammopathy → worse prognosis, heme/onc engagement. (PG severity scores are schema-blocked TS calculators; captured narratively.)
   inputs: systemic_toxicity_extent_of_disease, ulcer_progression_rate
   advance: localised vs moderate-severe vs fulminant tier + prognostic-modifier overlay assigned
9. 9TREATMENT
   CARDINAL RULE: NO surgical debridement / aggressive surgery (pathergy → catastrophic enlargement); manage peristomal/postsurgical PG conservatively with immunosuppression; graft/essential surgery only under immunosuppressive cover. Ladder by extent: localised → ultrapotent topical corticosteroid (clobetasol) or intralesional triamcinolone, topical tacrolimus + meticulous moist non-adherent wound care + analgesia + compression if leg oedema (non-pharm). Moderate-severe / rapidly progressive → systemic prednisone 0.5-1 mg/kg OR ciclosporin (STOP GAP — comparable efficacy, choose on toxicity); pulse methylprednisolone for fulminant. Refractory / steroid-sparing → infliximab (RCT-supported, esp. IBD-associated), adalimumab, IVIG, mycophenolate, azathioprine, cyclophosphamide. TREAT THE ASSOCIATED DISEASE (IBD/arthritis/heme drives the skin). Gate on pregnancy, renal/hepatic function, TNF infection screen.
   inputs: creatinine, pregnancy_status
   advance: no-debridement rule enforced; extent-appropriate immunosuppression + wound care + analgesia started; associated disease addressed; agent gated on comorbidity/pregnancy
10. 10DISPOSITION
    Outpatient for localised disease (criteria-based diagnosis, exclusion + associated-disease workup, topical/intralesional ± oral immunosuppression, dermatology follow-up). Admit for rapidly progressive / fulminant / systemically toxic PG, IV immunosuppression, severe uncontrolled pain, or a pathergy-driven enlargement after misdirected surgery requiring multidisciplinary stabilisation. Route associated-disease ownership OUT by engine_id (GI/heme/rheum) while retaining skin + immunosuppression ownership.
    inputs: systemic_toxicity_extent_of_disease
    advance: disposition documented; admission only for fulminant/toxic/uncontrolled-pain criteria; specialty co-management arranged
11. 11MONITORING
    Disease: ulcer size + pain trajectory + healing (response within ~1 month of starting immunosuppression is itself a Maverakis minor criterion); STOP GAP benchmark ~47% healed by 6 months on prednisolone OR ciclosporin. Drug safety: prednisone (glucose/BP/bone), ciclosporin (BP + creatinine, CKD-EPI), azathioprine/MMF (CBC/LFT), biologics (infection/TB reactivation). Taper guided by response with transition to a steroid-sparing agent. Track associated-disease activity (IBD/arthritis/heme) as it drives the skin.
    inputs: creatinine, lft
    actions: panel.cbc, panel.lft, panel.renal
    advance: ulcer/pain trajectory assessed at the agent-appropriate interval; drug-class safety labs on schedule; associated-disease activity tracked
12. 12FOLLOWUP
    Chronic surveillance: continued meticulous moist non-adherent wound care + analgesia, slow steroid taper with steroid-sparing maintenance, recurrence vigilance (PG recurs in ~28-30% — STOP GAP), pathergy education (avoid elective surgery/debridement; flag PG to any future surgeon; perioperative immunosuppressive cover if surgery unavoidable), cribriform-scar counselling, and ongoing associated-disease monitoring (repeat heme screen if new cytopenia; IBD/arthritis activity). Dermatology continuity for any systemic agent.
    inputs: associated_systemic_disease, pathergy_or_trauma_localisation
    actions: workup.chronic_pruritus
    advance: wound-care + taper + pathergy education + recurrence + associated-disease surveillance plan documented