A new expert consensus outlines diagnostic guidelines for MCD aims to accelerate diagnosis, guide treatment and enable research.
In a significant advancement for dermatology and gastroenterology, a panel of US experts has reached consensus on the first formal diagnostic criteria for metastatic cutaneous Crohn disease.
MCD is a rare skin manifestation of Crohn disease that appears in sites not directly connected to the gastrointestinal tract. It can affect the genitals, oral cavity or other skin regions, typically presenting with knife-like ulcers, genital swelling or lymphedema.
The criteria, developed through a rigorous five-round Delphi process, aim to standardise diagnosis across clinical settings, reduce diagnostic delays and support translational research.
The panel identified both major and minor clinical features for genital and oral MCD, establishing clear thresholds for diagnosis. Notably, biopsy is not required, although specific histological findings can support the diagnosis.
While MCD remains rare, its impact on quality of life – particularly in sensitive areas like the genitals and mouth – can be severe. The consensus criteria are expected to aid earlier intervention, improve clinical decision-making and facilitate inclusion of MCD in Crohn-related research.
The study, published in JAMA Dermatology, also calls for broader data sharing and international validation to refine these criteria and support equitable diagnosis globally.
“Formal MCD diagnostic criteria will expand clinical care and research by enabling future diagnostic code validation, crystallising a more uniform disease entity for the purposes of translational research and allowing the development of more formalised outcome measures aimed at treatment response,” the authors wrote.
Sydney dermatologist Associate Professor Stephen Shumack noted that it was quite a small Delphi group with “no patient representatives, and restricted just to the US with no international participants”.
“I am not sure that these diagnostic criteria will help with clinical practice as MCD is rare, but not that rare, with most Australian dermatologists seeing at least a few cases during their training, and the clinical presentations have been well described previously,” he told Dermatology Republic.
“I am surprised biopsy histopathology consistent with the diagnosis for MCD is a ‘minor criteria’, as patients that we see with the presumptive clinical diagnosis of MCS would normally have a skin biopsy, and the presence of the typical features are helpful to confirm the diagnosis.”
The multidisciplinary panel of dermatologists, dermatopathologists and gastroenterologists employed a modified Delphi method, surveying participants across five rounds to reach consensus on clinical and histologic criteria.
Participants were selected based on their expertise in MCD and related conditions, such as vulvar diseases and inflammatory bowel disease (IBD)-associated dermatoses.
The panel agreed to categorize MCD into three types—genital, oral and other. For genital MCD, diagnosis requires either two major criteria, or one major and one minor criterion or three minor criteria.
Major genital criteria include:
- Knifelike ulcerations
- Genital swelling or oedema
- Lymphedematous changes
Minor genital criteria include:
- Fissuring
- Nonhealing genital ulcers
- Perianal skin tags
For oral MCD, a known history of inflammatory bowel disease plus one minor criterion – such as linear oral ulcers or granulomatous cheilitis – was deemed sufficient for diagnosis.
Although histologic findings such as noncaseating granulomas and lymphoplasmacytic inflammation were considered highly suggestive, the panel agreed that a biopsy was not necessary for diagnosis, reflecting the condition’s clinical heterogeneity.
The authors said establishing diagnostic criteria for MCD was a vital step forward. They said standardised criteria would enable earlier and more accurate diagnosis; promote uniformity in clinical trials; allow for diagnostic code validation in medical records and insurance datasets and facilitate large-scale epidemiologic studies.
The criteria also opened the door to the development of outcome measures for treatment efficacy, currently a major gap in MCD management.
“Diagnostic criteria are a critical first step in better classifying and diagnosing patients, which will, in turn, help with future translational and epidemiologic studies in understanding the pathophysiology of this recalcitrant condition,
“A reference standard set of diagnostic criteria will enable the validation of associated diagnostic code(s), which in turn may enable mining of larger datasets and insurance claims to identify risk factors associated with the development of MCD in individuals with intestinal CD.
“MCD could, in combination with other cutaneous manifestations of inflammatory bowel disease, be included in the clinical trial assessments of patients with intestinal Crohn disease and ensure due attention to cutaneous reactions in patients with intestinal Crohn disease.
“Diagnostic criteria will also promote more uniform translational efforts aimed at understanding the underlying pathophysiology of the condition, which in turn may help elucidate other conditions with similar phenotypic presentations such as intestinal Crohn disease or HS.
“In addition, having diagnostic criteria will hopefully increase disease awareness and reduce diagnostic delays, pain, and progressive skin deformity, especially in sensitive areas of the body such as the genitals, buttocks and mouth.”
The authors conceded the consensus panel had limitations. MCD is a rare condition, and clinical expertise was gathered across related fields (granulomatous diseases, vulvar diseases, autoinflammatory diseases, dermatopathology and gastroenterology), as experts on MCD alone are uncommon, and some exceptional clinical experts may not have been included if they were unknown to other Delphi panellists or their publication on the topic was limited or not recent.
“Nomenclature in the arena of rare conditions is challenging. Because of institutional review board constraints, recruitment was limited to the US only,” they wrote.
“Finally, while patients with MCD were recruited to participate, all five patients recruited felt they lacked the expertise or time required to participate in this type of Delphi panel and ultimately declined participation.
“Improved panel heterogeneity could be considered for future endeavours, and future review of final consensus statements by patients may enable patient participation without requiring the intensive time demands or technical expertise of a Delphi panel.”
Professor Shumack said that while it was an “interesting attempt at listing and classifying diagnostic criteria for MCD, it was “not all that useful in assisting with diagnosis or management of MCD clinical practice”.
“It would be interesting to see if the classification and list of criteria changed with a larger and broader group of experts were involved in a similar DELPHI process on this topic.”
