Pyoderma gangrenosumhttps://en.wikipedia.org/wiki/Pyoderma_gangrenosum
Pyoderma gangrenosum is a rare, inflammatory skin disease where painful pustules or nodules become ulcers that progressively grow. Pyoderma gangrenosum is not infectious. Treatments may include corticosteroids, ciclosporin, or various monoclonal antibodies. Though it can affect people of any age, it mostly affects people in their 40s and 50s.

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  • On the leg of a person with ulcerative colitis.
References Pyoderma Gangrenosum: An Updated Literature Review on Established and Emerging Pharmacological Treatments 35606650 
NIH
Pyoderma gangrenosum is a rare inflammatory skin disease classified within the group of neutrophilic dermatoses and clinically characterized by painful, rapidly evolving cutaneous ulcers with undermined, irregular, erythematous-violaceous edges. Pyoderma gangrenosum pathogenesis is complex and involves a profound dysregulation of components of both innate and adaptive immunity in genetically predisposed individuals, with the follicular unit increasingly recognized as the putative initial target.
 Pyoderma Gangrenosum: Treatment Options 37610614 
NIH
Pyoderma gangrenosum is a rare neutrophilic dermatosis that leads to exceedingly painful ulcerations of the skin. Although the exact pathogenesis is not yet fully understood, various auto-inflammatory phenomena with increased neutrophil granulocyte activity have been demonstrated. Despite the limited understanding of the pathogenesis, it is no longer a diagnosis of exclusion, as it can now be made on the basis of validated scoring systems. However, therapy remains a major multidisciplinary challenge. Various immunosuppressive and immunomodulatory therapies are available for the treatment of affected patients. In addition, concomitant topical pharmacologic therapy, wound management and pain control should always be addressed. Corticosteroids and/or cyclosporine remain the systemic therapeutics of choice for most patients. However, in recent years, there has been an increasing number of studies on the positive effects of biologic therapies such as inhibitors of tumour necrosis factor-α; interleukin-1, interleukin-17, interleukin-23 or complement factor C5a. Biologics have now become the drug of choice in certain scenarios, particularly in patients with underlying inflammatory comorbidities, and are increasingly used at an early stage in the disease rather than in therapy refractory patients.