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The prevalence of pyoderma gangrenosum (PG) is unknown. Estimates have suggested that approximately three cases of PG per million of the population occur per year, with most large referral centers seeing one to two cases per year.1 It has been reported in all age groups but mainly affects adults between the ages of 40 and 60 years.2 Most reported series of patients with PG indicate a moderate preponderance of females. PG often occurs in patients who have other diseases (arthritis, inflammatory bowel disease, hematologic dyscrasias, etc.), but is not a manifestation or complication of these diseases and its clinical course is usually unrelated to their severity or activity.3
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The etiology of PG is unknown, and its pathogenesis poorly understood. Based on the presence of a lymphocytic infiltrate at the active advancing border of PG lesions, it has been postulated that lymphocytic antigen activation occurs with cytokine release and neutrophil recruitment. This may take place not only in the skin but also in other tissues such as the lung, intestine, and joints. The predominance of the neutrophilic infiltrate in established lesions of PG have led to its classification as one of the neutrophilic dermatoses.4 Clinical (and to an extent histologic) overlap occurs with the other dermatoses in this category, especially atypical or bullous forms of Sweet syndrome (see Chapter 32). Several of the neutrophilic dermatoses (Sweet syndrome, erythema elevatum diutinum, subcorneal pustular dermatosis, and PG) share an association with immunoglobulin ...