Pyoderma Gangrenosum: What to Include in the Differential Diagnosis

Pyoderma gangrenosum (PG) is a chronic, recurrent condition characterized by cutaneous ulceration (Figure). In half of patients, PG is associated with an underlying illness, such as inflammatory bowel disease, RA, SLE, or a lymphoproliferative disorder.⁷

Clinically, lesions of PG are usually located on the lower extremities and occur most often at multiple sites. Lesions develop at sites of trauma but can also develop spontaneously. The initial lesion is a small papule that rapidly becomes a pustule. The center becomes necrotic and spreads outward. The final ulcer is characterized by a purulent base and a ragged, undermined violaceous border. The ulcers are often painful.

Although these lesions have a characteristic presentation, the differential diagnosis of PG is wide-ranging. Infectious processes-including deep fungal, bacterial, mycobacterial, and herpetic infections-must be ruled out. It is prudent to send skin biopsy specimens for both histologic assessment and tissue culture.

Vasculitis is another process that can mimic PG; it can be excluded on the basis of histologic examination. Other conditions in the differential diagnosis include ulcers secondary to arterial or venous insufficiency, factitial ulcers, and ulcers resulting from brown recluse spider bites.

Because PG is frequently associated with underlying systemic disorders, a thorough work-up is warranted in patients presenting with this condition. The work-up should include studies of the GI tract, serologic studies, radiographic examination, complete blood cell count, bone marrow aspirate and biopsy, and serum and urine protein electrophoresis and immunoelectrophoresis.

Treatment includes both local and systemic therapies. Patients with underlying illness may demonstrate improvement of the cutaneous disease once the underlying condition is treated.⁸ Options for systemic therapy include glucocorticoids (oral or pulse intravenous), dapsone, minocycline, azathioprine, 6-mercaptopurine, chlorambucil, cyclosporine,⁹ and pulse intravenous cyclophosphamide.¹⁰ Surgical manipulation of ulcers is best avoided because of the possibility of pathergy, a phenomenon whereby trauma induces new lesions.

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