Medical Calculators

Ulcerative PG Diagnostic Corridor

Delphi consensus criteria and the PARACELSUS score, scored together, with unanswered findings kept explicit and each framework reported separately.

Decision support, not a diagnosis. Both instruments were derived and validated for the ulcerative subtype only, and neither replaces assessment of mimickers by an experienced clinician. A threshold-met result does not establish PG or authorize treatment. Nothing entered here is stored or transmitted. Use a non-identifying case code. Evidence reviewed August 2026.

Free · right now

Look at the wound

0 of 7 answered
Reddish violaceous wound border

Erythematous to livid rim at the advancing edge. Present in about 98 percent of PG cases in the PARACELSUS derivation cohort.

PARACELSUS R · 3 pts
Peripheral erythema at the ulceration site

Delphi minor criterion 5 requires peripheral erythema, an undermined border, and tenderness together.

Delphi minor 5 · part
Undermined wound border

The edge overhangs the bed and a probe passes beneath intact skin.

PARACELSUS U · 1 ptDelphi minor 5 · part
Tenderness at the ulceration site

Record examination tenderness independently of the patient's spontaneous pain score.

Delphi minor 5 · part
Characteristically irregular ulcer shape

Bizarre, geographic or serpiginous outline rather than the round or oval shape of a vascular ulcer.

PARACELSUS C · 2 pts
Multiple ulcerations, at least one on an anterior lower leg

Delphi minor 6. Both parts are required.

Delphi minor
Cribriform or wrinkled paper scarring at healed sites

Delphi minor 7. Highly discriminating in the derivation data, and easy to miss unless you look at old sites.

Delphi minor
Free · two minutes

Ask the patient

0 of 5 answered
Rapidly progressive ulcer

PARACELSUS defines a progressive course as an ulcer developing or progressing within 6 weeks.

PARACELSUS P · 3 pts
Pain above 4 of 10 on a visual analogue scale

PARACELSUS extreme-pain criterion. This does not substitute for examination tenderness in Delphi minor criterion 5.

PARACELSUS E · 2 pts
Lesion localized to a site of trauma

PARACELSUS localization criterion, including surgical sites, needle sticks, debridement, and stoma sites.

PARACELSUS L · 2 pts
Pathergy documented

Delphi minor criterion 2. Record a lesion induced or worsened by trauma; the ulceration should extend beyond the area of trauma.

Delphi minor
Papule, pustule or vesicle that ulcerated within 4 days

Delphi minor 4. Requires a specific history of the primary lesion and its speed of breakdown.

Delphi minor
Hours to days

Records & exclusion workup

0 of 4 answered
Inflammatory bowel disease or inflammatory arthritis

Delphi minor 3 counts only these two. PARACELSUS counts any associated systemic disease.

PARACELSUS S · 1 pt sharedDelphi minor
Other PG associated systemic disease

Haematologic malignancy, myelodysplastic syndrome, monoclonal gammopathy especially IgA, solid tumour, hidradenitis suppurativa, autoinflammatory syndromes. Feeds PARACELSUS only.

PARACELSUS S · 1 pt shared
Infection excluded by tissue culture and special stains

Delphi minor 1. Bacterial, mycobacterial and fungal. Surface swabs do not count.

Delphi minor
Relevant differential diagnoses assessed and excluded

PARACELSUS major criterion. Vascular arterial and venous, vasculitis, calciphylaxis, malignancy, exogenous or factitial, infectious.

PARACELSUS A · 3 pts
Invasive or delayed

Tissue & time

0 of 4 answered
Ulcer-edge biopsy for the Delphi major criterionDELPHI GATE

Delphi requires a neutrophilic infiltrate in a biopsy from the ulcer edge. This tool does not recommend whether to biopsy; use clinical judgement to balance evaluation of mimickers against pathergy risk.

Amelioration after immunosuppressive therapy

PARACELSUS response criterion. Record separately from the more specific Delphi one-month ulcer-size criterion.

PARACELSUS A2 · 2 pts
Ulcer decreased in size within 1 month of starting immunosuppression

Delphi minor criterion 8. Cannot be known before treatment starts, so an unresolved answer is appropriate when treatment has not yet been observed.

Delphi minor
Suppurative inflammation on histopathology

PARACELSUS additional criterion. This is recorded separately from Delphi's ulcer-edge neutrophilic-infiltrate requirement.

PARACELSUS S · 1 pt

PARACELSUS corridor

0 of 20
Still reachableup to 20
0101120
DocumentedStill open
PARACELSUS at threshold 11
Not yet determined
The corridor spans the threshold. The documented score is currently below it, with up to 20 additional points unresolved.

Delphi consensus

Major criterion unresolved — ulcer-edge histology is not documented. Delphi cannot be met until this is resolved.
Minor criteria · 4 of 8 required
1
2
3
4
5
6
7
8
0 confirmed, up to 8 if the open items resolve in favour. Four are required.
Delphi consensus criteria
Not yet determined
The major criterion is the blocker. Nothing else you document can substitute for it.

Unanswered information

Completeness list only. It does not estimate diagnostic yield, rank tests, or recommend biopsy or treatment.

1
Reddish violaceous wound border
PARACELSUS: 3 points. bedside assessment
2
Peripheral erythema at the ulceration site
Delphi: component of combined minor criterion 5. bedside assessment
3
Undermined wound border
PARACELSUS: 1 point; Delphi: component of combined minor criterion 5. bedside assessment
4
Tenderness at the ulceration site
Delphi: component of combined minor criterion 5. bedside assessment
5
Characteristically irregular ulcer shape
PARACELSUS: 2 points. bedside assessment
6
Multiple ulcerations, at least one on an anterior lower leg
Delphi: one minor criterion. bedside assessment
7
Cribriform or wrinkled paper scarring at healed sites
Delphi: one minor criterion. bedside assessment
8
Rapidly progressive ulcer
PARACELSUS: 3 points. bedside assessment
9
Pain above 4 of 10 on a visual analogue scale
PARACELSUS: 2 points. bedside assessment
10
Lesion localized to a site of trauma
PARACELSUS: 2 points. bedside assessment
11
Pathergy documented
Delphi: one minor criterion. bedside assessment
12
Papule, pustule or vesicle that ulcerated within 4 days
Delphi: one minor criterion. bedside assessment
13
Inflammatory bowel disease or inflammatory arthritis
PARACELSUS: shared systemic-disease point; Delphi: one minor criterion. chart review
14
Other PG associated systemic disease
PARACELSUS: shared systemic-disease point. chart review
15
Infection excluded by tissue culture and special stains
Delphi: one minor criterion. diagnostic workup
16
Relevant differential diagnoses assessed and excluded
PARACELSUS: 3 points. diagnostic workup
17
Amelioration after immunosuppressive therapy
PARACELSUS: 2 points. observed treatment response
18
Ulcer decreased in size within 1 month of starting immunosuppression
Delphi: one minor criterion. observed treatment response
19
Suppurative inflammation on histopathology
PARACELSUS: 1 point. histopathology or biopsy information
20
Ulcer-edge biopsy for the Delphi major criterion
Delphi: required major criterion. histopathology or biopsy information

Reading the two together

Still open. At least one framework remains indeterminate because scoring information is unanswered.

Ulcer-edge histology is unresolved. Delphi cannot be met without its major criterion. Biopsy can also help evaluate mimickers, but this calculator does not recommend whether or when to biopsy; balance the clinical need against pathergy risk.

Where these numbers come from+
Instrument & thresholdReference standard populationSensSpecAUCPPV
PARACELSUS ≥ 10Jockenhöfer 2019 derivation, 60 lower-extremity PG vs 50 venous leg ulcers100%100%n/rn/r
PARACELSUS ≥ 10Moelleken 2026, 1403 ulcers from 14 centres in 7 countries, 180 PG across 85 wound entities100.0%93.2%n/r68.4%
PARACELSUS > 10 (≥ 11)Moelleken 2026, same cohort98.3%96.8%n/r81.9%
PARACELSUS ≥ 10Ji-Xu 2023, ulcerative PG cases vs deliberately selected mimicker controls95.9%4.7%0.55n/r
PARACELSUS ≥ 10Haag 2021, expert-confirmed PG cohort only, no controls89%n/an/rn/r
Delphi, major + 4 of 8 minorMaverakis 2018 derivation, 65 published ulcerative PG vs 48 mimickers, k-fold CV with imputation86%90%n/rn/r
Delphi, major + 4 of 8 minorJi-Xu 2023, cases vs mimickers, complete-case analysis88.0%90.5%0.89n/r
Delphi, major + 4 of 8 minorHaag 2021, expert-confirmed PG cohort only74%n/an/rn/r
Su 2004, for contextJi-Xu 202386.2%69.6%0.74n/r

Performance depends on the comparator population. PARACELSUS specificity was 93.2 to 96.8 percent in the broad mixed-wound cohort studied by Moelleken and 4.7 percent in the selected mimicker controls studied by Ji-Xu. These estimates are not interchangeable and should not be applied as patient-specific probabilities.

Agreement is limited. Ji-Xu reported a Cohen kappa of 0.15 between Delphi and PARACELSUS. Haag found that all three frameworks agreed for 72 percent of an expert-confirmed PG cohort, with a Fleiss kappa of 0.44. A discordant result should prompt review of the exact item definitions and the differential diagnosis.

Histopathology has different roles in the frameworks. Delphi requires an ulcer-edge biopsy showing a neutrophilic infiltrate; PARACELSUS separately awards 1 point for suppurative inflammation. A negative or nonspecific biopsy should be interpreted in clinical context rather than assumed to be a false negative.

References

  1. Maverakis E, Ma C, Shinkai K, et al. Diagnostic criteria of ulcerative pyoderma gangrenosum: a Delphi consensus of international experts. JAMA Dermatol. 2018;154(4):461-466.
  2. Jockenhöfer F, Wollina U, Salva KA, Benson S, Dissemond J. The PARACELSUS score: a novel diagnostic tool for pyoderma gangrenosum. Br J Dermatol. 2019;180(3):615-620.
  3. Haag C, Hansen T, Hajar T, et al. Comparison of three diagnostic frameworks for pyoderma gangrenosum. J Invest Dermatol. 2021;141(1):59-63.
  4. Min MS, Kus K, Wei N, et al. Evaluating the role of histopathology in diagnosing pyoderma gangrenosum using Delphi and PARACELSUS criteria. Br J Dermatol. 2022;186(6):1035-1037.
  5. Ji-Xu A, Liakos W, Merleev A, Brüggen MC, Nelson CA. Assessing the discriminatory ability of diagnostic criteria for ulcerative pyoderma gangrenosum and its mimickers. JAMA Dermatol. 2023;159(3):337-338.
  6. Moelleken M, Ortega-Loayza AG, Busch D, et al. Validation of PARACELSUS score performance for the diagnosis of pyoderma gangrenosum: an international multicenter study with 1403 cases. J Am Acad Dermatol. 2026;94(6):1738-1746.