A case of pyoderma gangrenosum induced by insulin

Pyoderma gangrenosum (PG) is a rare auto-inflammatory, neutrophilic, ulcerative disorder characterised by acutely painful, rapidly spreading, sterile ulcers over the trunk and lower limbs. The pathogenic mechansim of PG is under constant evolution and drugs are emerging to be a an important trigger. In the literature, 52 cases of drug-induced PG have been documented, of which cocaine laced with levamisole has shown most direct association, with a mean Naranjo score of 9. Other drugs probably associated with PG are isotretinoin, sunitinib, and propylthiouracil. We describe a case of a 59-year-old male who had multiple well-defined ulcers with a violaceous, undermined edge limited to the site of subcutaneous injection of insulin. Histopathological examination showed psoriasiform hyperplasia in the epidermis, with abundant infiltration of neutrophils in the dermis, consistent with the clinical diagnosis of PG. As per the modified Naranjo algorithm, the patient's total score was 7, indicating insulin to be the probable causative agent in our case. So, compiling temporal localisation of lesions to the site of administration of insulin and clinical, histopathological, and Naranjo score evidence all prompt the diagnosis of PG. Insulin stimulates the release of matrix-metalloproteinases 9 which acts as endopeptidases and also results in the chemotaxis of neutrophils, causing ulcer formation. This is the first case reporting PG triggered by insulin.