[Pyoderma gangrenosum as an initial manifestation of systemic disease].

In order to describe the clinical features and diagnostic challenges of pyoderma gangrenosum, we present the case of a 39-year-old woman who consulted for ulcerated lesions on the lower limbs and left forearm, initially secondary to dog bites of one week's evolution. Despite surgical debridement and empirical antibiotic therapy, the patient developed new cutaneous lesions, fever, and hemodynamic instability, requiring invasive mechanical ventilation. During hospitalization, newly diagnosed hyperthyroidism and hypogammaglobulinemia due to IgG deficiency -findings consistent with common variable immunodeficiency- were documented. The absence of microbiological isolation, poor response to conventional therapeutic measures, and the emergence of new ulcers at sites of minimal trauma raised the suspicion of pyoderma gangrenosum, which was subsequently supported by clinical criteria and histopathological findings on skin biopsy. Early recognition of this entity is essential to prevent iatrogenic interventions, initiate timely immunomodulatory treatment, and reduce associated morbidity and mortality. This case highlights the importance of considering pyoderma gangrenosum in the differential diagnosis of atypical cutaneous ulcers, particularly in patients with underlying immune dysfunction.