Cutaneous Amebiasis. Increasingly, cutaneous amebiasis is being recognized as complicating other forms of amebiasis. Surgical drainage from an amebic abscess in the liver or from the pericolic region after an appendectomy, or leakage from a perirectal or perianal abscess, allows implantation of amebae into small surface lesions, particularly around the drainage area. Perianal amebiasis can arise by direct spread from the rectum. Cutaneous ulcers, however they originate, are almost always tender, painful, and malodorous, but usually provoke little inflammation in adjacent tissue. Ulcers in the skin are generally shallow, and the edges are well defined: the floor of the ulcer is covered with a dirty gray slough (Fig. 1.11 A,B). Amebic ulcers of the trunk resemble those of the colon in that they are undermined and caused by extensive lytic necrosis. They contain few neutrophiles and the trophozoites are concentrated in the exudate from the depths of the keratin pits, under the margin of the ulcer, and deep in the lesion along the line between necrotic and viable tissue. Only the trophozoite form of amebiasis is present in the skin, the cyst form never being found in man other than in the intestinal contents.

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Fig. 1.11A,B. Amebic ulcers of the skin in three different patients. (A) Large ulcer of the skin of the anterior abdominal wall which developed after drainage of an amebic abscess in the liver. Amebic skin ulcers are usually shallow, painful and malodorous, the edges are well defined, and the floor of the ulcer is covered with a dirty gray slough. The exudate near the margin of the ulcer may contain E. histolytica trophozoites. (B) Cutaneous ulcer which developed at the site of a midline surgical incision. Note a surgical drainage site nearby (upper left).

Amebiasis of anal skin (Fig. 1.11C,D), genital skin, cervix, and penis causes hyperplasia of squamous epithelium punctuated by small shallow ulcers containing trophozoites. The hyperplastic epithelium raises the surface and gives it a "cauliflower-like" appearance resembling a squamous cell carcinoma; indeed, its gross appearance may cause the unwary clinician to misdiagnose perineal or genital amebiasis as a carcinoma or mycotic infection. Cutaneous infection is unlikely outside endemic areas unless the patient is already known to have severe amebiasis. Where the disease is common, cutaneous ulceration is not infrequent, but despite this the etiology is not always recognized immediately.

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Fig. 1.11C,D. (C) Extensive perianal and perineal bleeding from cutaneous ulcers caused by leakage from a perirectal amebic abscess.(D) Extension of colorectal amebiasis to anal skin in a 39-year-old man from the Democratic Republic of the Congo. When trophozoites invade squamous epithelium, they cause epithelial hyperplasia, as shown here, which can be easily mistaken for squamous cell carcinoma. After trophozoites were identified in the biopsy specimen, the patient was treated with emetine hydrochloride and the lesion quickly healed. (D from D.H. Connor and F.W. Chandler (eds):Pathology of Infectious Diseases, Stamford, Ct, Appelton & Lange, 1997).