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derm.cellulitis.core.v1PRODUCTION
derm.cellulitis.core.v1

Cellulitis & erysipelas (dermatology lens)

dermatologyacutesubacuteadult
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12/12 authored

Canonical 12-phase frame with authored status for this dossier.

Current phase

Frame

Detailed

Frame as a SKIN-BARRIER infective process vs the dermatology mimic spectrum — ~30% of admitted "cellulitis" is pseudocellulitis (Raff JAMA Dermatol 2016; Levell BJD 2011). Erysipelas (superficial dermis + lymphatics, sharply raised border) vs cellulitis (deeper dermis/subcutis, indistinct border) (NICE NG141 2019). Systemic-sepsis and necrotizing concerns are routed OUT, not authored here.

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Patient inputs (16)

Raised sharply demarcated border → erysipelas; indistinct → cellulitis; geometric/linear → contact dermatitis (NICE NG141 2019; IDSA 2014 SSTI Stevens)

Itch-dominant favors dermatitis (stasis/contact); pain/tenderness-dominant favors cellulitis (Raff JAMA Dermatol 2016 — pruritus has high LR for pseudocellulitis)

Tinea pedis / interdigital maceration / eczema fissure / ulcer is the dominant modifiable derm risk factor and recurrence driver (Dupuy BMJ 1999; NICE NG141 2019)

Lymphedema / chronic venous insufficiency is the strongest non-portal recurrence risk and a key mimic substrate (Cox BJD 2006; McNamara case-control)

Stasis dermatitis is THE most common cellulitis mimic; chronic bilateral changes (hemosiderin, varicosities, lipodermatosclerosis) reframe the prior (Raff JAMA Dermatol 2016; Hirschmann JAAD 2012)

Fever raises infective prior and Eron class; afebrile bilateral itch-dominant red leg argues stasis dermatitis (Eron 2003; Raff JAMA Dermatol 2016)

Diabetic skin barrier compromise + neuropathy alters portal, healing, and pathogen spectrum — derm wound-care threshold (IDSA 2014 SSTI Stevens; IWGDF 2023)

Bilateral lower-leg erythema is rarely infective cellulitis — strongest single pseudocellulitis discriminator (Raff JAMA Dermatol 2016 — bilaterality argues stasis dermatitis)

Pain out of proportion / dusky skin / bullae / crepitus / anesthesia → route OUT to id.necrotising-fasciitis.core.v1 (IDSA 2014 SSTI Stevens — surgical emergency, not authored here)

Hypotension / systemic toxicity → route OUT to id.sepsis.core.v1 (SSC 2021; Eron 2003 class IV — sepsis pathway not authored here)

Rule out DVT mimic when calf-dominant / pretest DVT non-trivial → route to cardio.dvt.core.v1 if positive (NICE NG141 2019)

Atypical morphology + lower derm-referral and biopsy threshold (IDSA 2014 SSTI Stevens — broader pathogen diversity)

Normal WBC + bilateral itch-dominant erythema lowers infective prior (Raff JAMA Dermatol 2016 — inflammatory markers poorly discriminate but feed the chain)

Serial CRP trend supports response-to-therapy and IV→PO timing; very low CRP argues against cellulitis (NICE NG141 2019)

Antibiotic-safety gating for the derm regimen (avoid doxycycline/TMP-SMX near term) (NICE NG141 2019)

Renal dosing for cephalexin / TMP-SMX in the derm PO regimen (IDSA 2014 SSTI Stevens)

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Severity triggers (8)

8 need judgement
  • informationallife_threateningnecrotising_features_route_out
    Pain out of proportion, dusky/violaceous skin, hemorrhagic bullae, crepitus, cutaneous anesthesia, or rapidly advancing margin (IDSA 2014 SSTI Stevens)
    Trigger could not be auto-evaluated — needs clinician judgement.
  • informationalseveresystemic_toxicity_route_to_sepsis
    qSOFA ≥2, hypotension on adequate fluids, or Eron IV systemic toxicity with skin source (SSC 2021; Eron 2003)
    Trigger could not be auto-evaluated — needs clinician judgement.
  • informationalseverenon_response_at_48_72h
    Erythema advances beyond the dated marked border or systemic features at 48-72 h despite appropriate narrow-spectrum therapy (IDSA 2014 SSTI Stevens; NICE NG141 2019)
    Trigger could not be auto-evaluated — needs clinician judgement.
  • informationalmoderatedvt_mimic_route_out
    Calf-dominant pain/swelling, Wells-DVT not low, unilateral with DVT risk factors — compression Doppler indicated (NICE NG141 2019)
    Trigger could not be auto-evaluated — needs clinician judgement.
  • informationalmoderateskin_barrier_breakdown_high_risk
    Extensive skin-barrier failure: ulcerated limb, brittle diabetic foot skin, severe lymphedematous skin, widespread eczema fissuring as portal (Dupuy BMJ 1999; IWGDF 2023)
    Trigger could not be auto-evaluated — needs clinician judgement.
  • informationalmildpseudocellulitis_stop_antibiotics
    Bilateral lower-leg erythema, pruritus-dominant, afebrile, normal WBC, chronic stasis/varicose/hemosiderin changes — stasis dermatitis, not infection (Raff JAMA Dermatol 2016)
    Trigger could not be auto-evaluated — needs clinician judgement.
  • informationalmildrecurrent_same_limb_prophylaxis
    ≥2 episodes/year of cellulitis in the same limb (Thomas NEJM 2013 PATCH II)
    Trigger could not be auto-evaluated — needs clinician judgement.
  • informationalmildacute_lipodermatosclerosis_mimic
    Acutely tender, woody, indurated medial-supramalleolar plaque on chronic venous disease, afebrile, no leukocytosis (Bruce JAAD 2002 — lipodermatosclerosis)
    Trigger could not be auto-evaluated — needs clinician judgement.

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Recommended regimen

Confirmed non-purulent cellulitis / erysipelas — narrow-spectrum (derm-first)
axis: cellulitis_derm_narrow_spectrumstep 1 - Step 1 — Confirm diagnosis before any antibiotic
Selected step "Step 1 — Confirm diagnosis before any antibiotic" — Acute unilateral warm tender expanding erythema with fever and/or leukocytosis; pseudocellulitis (bilateral, itch-dominant, chronic stasis changes, afebrile) excluded
  • diagnostic_confirmation_no_antibiotic_if_pseudocellulitis
    first line
    decision_gate
    triggers: bilateral_erythema, pruritus_dominant, afebrile_chronic_stasis
    Raff JAMA Dermatol 2016 — 30% of admitted cellulitis is pseudocellulitis; 92% received unnecessary antibiotics. Stasis dermatitis is treated as dermatitis (emollient + topical steroid + compression), NOT antibiotics.

outpatient playbook — drug actions (4)

  1. 1. cephalexin (non-purulent, confirmed cellulitis)
    rxcui 2231
    500 mg • PO • QID × 5-7 d
    trigger: Confirmed non-purulent cellulitis, Eron I-II, no MRSA risk (IDSA 2014 SSTI Stevens; Hepburn 2004)
    Narrow streptococcal/MSSA cover; 5 d non-inferior to 10 d (Hepburn 2004)
  2. 2. penicillin V (erysipelas)
    rxcui 7984
    500 mg • PO • QID × 5-7 d
    trigger: Sharply demarcated raised erythema + abrupt fever = erysipelas (streptococcal) (IDSA 2014 SSTI Stevens)
    Streptococcal-targeted narrow agent for erysipelas
  3. 3. clindamycin (penicillin anaphylaxis)
    rxcui 2582
    300-450 mg • PO • QID × 5-7 d
    trigger: Severe penicillin allergy (IDSA 2014 SSTI Stevens)
    β-lactam allergy backup; C. difficile counsel
  4. 4. topical/oral antifungal for tinea pedis (parallel)
    per agent • topical/PO • until clear + 4 wk
    trigger: Interdigital tinea / toe-web maceration portal (Dupuy BMJ 1999)
    Eradicate the modifiable portal — recurrence prevention starts at episode 1

Auto-drafted A&P note

outpatient

Subjective

- Possible entry pathways: Unilateral warm, tender, expanding lower-leg erythema (IDSA 2014 SSTI Stevens — classic non-purulent cellulitis; NICE NG141 2019); Sharply demarcated, raised, indurated erythema (erysipelas — superficial dermis + lymphatics; NICE NG141 2019; IDSA 2014 SSTI Stevens); Acute "red leg" on a background of stasis dermatitis / lymphedema / leg ulcer / tinea pedis — high pseudocellulitis prior (Raff JAMA Dermatol 2016; David BJD 2011).

Objective

- No vitals, labs, or imaging entered for this encounter.

Assessment

**Cellulitis & erysipelas (dermatology lens)** (derm.cellulitis.core.v1).
Phenotype framing: Terminal derm differential with pivot findings: cellulitis vs stasis dermatitis (bilaterality + pruritus + chronicity pivot) vs acute lipodermatosclerosis (woody induration + medial-supramalleolar + no fever pivot) vs contact dermatitis (geometric margin + vesicles + itch pivot) vs DVT (calf tenderness + Wells + Doppler pivot — route to cardio.dvt.core.v1) vs erysipelas (raised sharply demarcated border + abrupt high fever pivot) vs lymphedema (chronic non-pitting + Stemmer pivot) vs gout (monoarticular + podagra + crystals pivot)
Scope: Frame as a SKIN-BARRIER infective process vs the dermatology mimic spectrum — ~30% of admitted "cellulitis" is pseudocellulitis (Raff JAMA Dermatol 2016; Levell BJD 2011). Erysipelas (superficial dermis + lymphatics, sharply raised border) vs cellulitis (deeper dermis/subcutis, indistinct border) (NICE NG141 2019). Systemic-sepsis and necrotizing concerns are routed OUT, not authored here.

No severity triggers fired against current inputs.

Plan

Regimen axis: **Confirmed non-purulent cellulitis / erysipelas — narrow-spectrum (derm-first)** — step "Step 1 — Confirm diagnosis before any antibiotic".
1. diagnostic_confirmation_no_antibiotic_if_pseudocellulitis (decision_gate, first line) — Raff JAMA Dermatol 2016 — 30% of admitted cellulitis is pseudocellulitis; 92% received unnecessary antibiotics. Stasis dermatitis is treated as dermatitis (emollient + topical steroid + compression), NOT antibiotics.

Setting playbook (outpatient) — Confirm cellulitis vs pseudocellulitis, start narrow-spectrum PO if infective, begin skin-barrier repair, recheck against a dated marked border at 48-72 h (Raff JAMA Dermatol 2016; NICE NG141 2019; Eron 2003)
2. cephalexin (non-purulent, confirmed cellulitis) 500 mg PO QID × 5-7 d — Confirmed non-purulent cellulitis, Eron I-II, no MRSA risk (IDSA 2014 SSTI Stevens; Hepburn 2004) (Narrow streptococcal/MSSA cover; 5 d non-inferior to 10 d (Hepburn 2004))
3. penicillin V (erysipelas) 500 mg PO QID × 5-7 d — Sharply demarcated raised erythema + abrupt fever = erysipelas (streptococcal) (IDSA 2014 SSTI Stevens) (Streptococcal-targeted narrow agent for erysipelas)
4. clindamycin (penicillin anaphylaxis) 300-450 mg PO QID × 5-7 d — Severe penicillin allergy (IDSA 2014 SSTI Stevens) (β-lactam allergy backup; C. difficile counsel)
5. topical/oral antifungal for tinea pedis (parallel) per agent topical/PO until clear + 4 wk — Interdigital tinea / toe-web maceration portal (Dupuy BMJ 1999) (Eradicate the modifiable portal — recurrence prevention starts at episode 1)

Non-pharmacologic actions:
- Mark AND date the erythema border with a skin marker; photograph (CREST 2005; NICE NG141 2019)
- Emollient barrier repair + limb elevation (NICE NG141 2019)
- Counsel: erythema often worsens 24-48 h before improving even on correct therapy (NICE NG141 2019)
- Compression once acute inflammation settles if chronic edema/lymphedema (Webb NEJM 2020)
- Stop antibiotics and switch to dermatitis plan (emollient + topical steroid + compression) if pseudocellulitis confirmed (Raff JAMA Dermatol 2016)

AVOID / contraindication checks:
- Penicillin anaphylaxis block cephalexin and penicillinV (IDSA 2014 SSTI Stevens — cross reactivity; use clindamycin)
- Clindamycin c diff counsel (IDSA 2014 SSTI Stevens)
- Doxycycline tmpsmx avoid pregnancy and near term (NICE NG141 2019 — route purulent/MRSA pregnancy cases to id.cellulitis.core.v1)
- Do not antibiotic treat stasis dermatitis (Raff JAMA Dermatol 2016 — pseudocellulitis is a dermatitis, not an infection)

Monitoring

Regimen monitoring:
- border trace against dated mark at 48-72h (CREST 2005; NICE NG141 2019)
- expect transient worsening first 24-48h counsel before escalation (NICE NG141 2019)
- CRP trend if baseline elevated (NICE NG141 2019)
- tinea pedis resolution at 4 weeks (Dupuy BMJ 1999)

Setting (outpatient) monitoring:
- Border re-trace vs dated mark at 48-72 h (CREST 2005)
- Symptom + systemic review at 48-72 h and day 7 (NICE NG141 2019)
- Return precautions: spreading beyond mark, fever, systemic features, necrotizing features (NICE NG141 2019)

Follow-up plan: DERMATOLOGY RECURRENCE PREVENTION (the core differentiator of this engine): eradicate + maintain tinea pedis control (recurrent risk if untreated — Dupuy BMJ 1999); lifelong emollient barrier repair for eczema/xerosis; compression + lymphedema therapy (decongestive) to reverse the recurrence substrate (Webb NEJM 2020 — compression halved recurrence); chronic venous insufficiency / stasis-dermatitis derm management; PATCH II penicillin V 250 mg BID × 12 mo if ≥2 episodes/year (Thomas NEJM 2013 — 45% relative recurrence reduction); derm referral for recurrent / atypical / ulcerated / diagnostically uncertain disease.
- Close-out criterion: recurrence-prevention + skin-barrier maintenance plan documented; derm referral made if criteria met

Monitoring phase: Border-trace progression at 48-72 h against the dated mark (CREST 2005); expect erythema to peak/worsen in first 24-48 h before improving even on correct therapy (NICE NG141 2019 — counsel to prevent premature escalation); CRP trend; if no improvement at 48-72 h reassess for mimic / abscess / wrong-spectrum / necrotizing before extending duration.

Disposition

Current setting: outpatient — Confirm cellulitis vs pseudocellulitis, start narrow-spectrum PO if infective, begin skin-barrier repair, recheck against a dated marked border at 48-72 h (Raff JAMA Dermatol 2016; NICE NG141 2019; Eron 2003)

Disposition criteria:
- Continue PO + skin-barrier plan if improving (NICE NG141 2019)
- Discharge OFF antibiotics with dermatitis plan if pseudocellulitis (Raff JAMA Dermatol 2016)
- Escalate to IV / inpatient / route OUT if Eron III-IV or non-response (Eron 2003)

Escalation triggers (move to higher acuity):
- No improvement / progression beyond mark at 48-72 h after mimic re-excluded → ED IV / route to id.cellulitis.core.v1 (IDSA 2014 SSTI Stevens)
- Necrotizing features → emergent surgery, route to id.necrotising-fasciitis.core.v1 (IDSA 2014 SSTI Stevens)
- Systemic toxicity / qSOFA ≥2 → route to id.sepsis.core.v1 (SSC 2021)

Earlier-Return Triggers

Return-precaution thresholds (watch for):
- [LIFE_THREATENING] Pain out of proportion, dusky/violaceous skin, hemorrhagic bullae, crepitus, cutaneous anesthesia, or rapidly advancing margin (IDSA 2014 SSTI Stevens)
- [SEVERE] qSOFA ≥2, hypotension on adequate fluids, or Eron IV systemic toxicity with skin source (SSC 2021; Eron 2003)
- [SEVERE] Erythema advances beyond the dated marked border or systemic features at 48-72 h despite appropriate narrow-spectrum therapy (IDSA 2014 SSTI Stevens; NICE NG141 2019)

Citations

- IDSA 2014 SSTI Guideline (Stevens et al, CID) + NICE NG141 Cellulitis & erysipelas (2019, evidence-reviewed 2024) + Eron 2003 / CREST 2005 severity classification + Raff & Kroshinsky JAMA Dermatol 2016 pseudocellulitis + Thomas NEJM 2013 PATCH II recurrence prophylaxis + Webb NEJM 2020 compression-for-recurrence + Hepburn 2004 short-course duration [PMID:24973422](https://pubmed.ncbi.nlm.nih.gov/24973422/)
- Cited evidence (PMID 27434444) [PMID:27434444](https://pubmed.ncbi.nlm.nih.gov/27434444/)
- Cited evidence (PMID 27806170) [PMID:27806170](https://pubmed.ncbi.nlm.nih.gov/27806170/)
- Cited evidence (PMID 23635049) [PMID:23635049](https://pubmed.ncbi.nlm.nih.gov/23635049/)
- Cited evidence (PMID 32786188) [PMID:32786188](https://pubmed.ncbi.nlm.nih.gov/32786188/)

Last reconciled with current guidelines: 2026-05-22.
References
  • IDSA 2014 SSTI Guideline (Stevens et al, CID) + NICE NG141 Cellulitis & erysipelas (2019, evidence-reviewed 2024) + Eron 2003 / CREST 2005 severity classification + Raff & Kroshinsky JAMA Dermatol 2016 pseudocellulitis + Thomas NEJM 2013 PATCH II recurrence prophylaxis + Webb NEJM 2020 compression-for-recurrence + Hepburn 2004 short-course duration — PMID:24973422
  • Cited evidence (PMID 27434444) — PMID:27434444
  • Cited evidence (PMID 27806170) — PMID:27806170
  • Cited evidence (PMID 23635049) — PMID:23635049
  • Cited evidence (PMID 32786188) — PMID:32786188