Chapter 33
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Pyoderma Gangrenosum at a Glance
 Pyoderma gangrenosum (PG) is a rare inflammatory disease of unknown etiology characterized by sterile neutrophilic infiltration of the skin. Similar neutrophilic infiltrations may occur in other organs. It is considered to be one of the groups of neutrophilic dermatoses and clinical and histological overlap with some of these may occur.PG is more frequent in female patients and occurs at any age, but usually between 40 and 60 years.The majority of patients with PG have other systemic diseases (such as arthritis, inflammatory bowel disease, hematological dyscrasias, malignant disease, etc.), but PG occurs independently of these disorders.PG may present as ulcerative, bullous, pustular, or vegetative variants. Clinical features of different variants sometimes overlap in individual patients but usually one variant dominates the clinical picture.There is no laboratory test or investigation that establishes the diagnosis of PG with certainty. The histopathological findings are not diagnostic but can be supportive of the diagnosis of PG in the appropriate clinical setting and are essential to rule out alternative diagnoses.Specified criteria (see below) suggest the diagnosis of PG, but other conditions (particularly infection, vascular disease, and malignancy) must be excluded.The mainstays of management are systemic immunosuppressive agents together with appropriate local and topical therapy.Ulcerative PG is a chronic disease. Remission usually requires months of treatment; maintenance therapy is necessary in many and relapses are common. Significant morbidity and mortality are experienced by patients with ulcerative and bullous PG.

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

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 ...

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