Clinical: painful ulcers associated with painful lymphadenopathy appear after an incubation period of 4-7 days; as opposed to syphilis, the chancre in chancroid has undermined edges and is covered by a gray-yellow exudate.
Histologic features: 3 distinct zones.
Surface zone: exudate, fibrin, and neutrophils with debris at the base of the ulcer.
Intermediate zone: wide area with prominent vascular proliferation and thromboses with vascular ectasia.
Deep zone: dense infiltrate of plasma cells and lymphocytes.
Diagnosis is presumptive, based upon histologic features +/- identification of the bacteria on special stains (bacteria have a "railroad track" or "school of fish" alignment of short rods).