Purple-red papules on foot

Diagnosis: Kaposi’s sarcoma

Classic Kaposi’s sarcoma is a rare mesenchymal tumor most often seen in elderly men of Mediterranean or Ashkenazi Jewish origin with an annual incidence in the United States of between 0.02% and 0.06%, with a peak occurring in the 5th to 8th decade of life.¹ (Two-thirds of cases develop after the age of 50.) Population-based studies in the United States have shown a male-to-female ratio of 4:1.¹

First described by the Hungarian dermatologist Moritz Kaposi in 1872, Kaposi’s sarcoma assumed prominence during the emerging HIV epidemic and is now the most common tumor in patients with acquired immune deficiency syndrome (AIDS).²

Recent research has implicated the human herpes virus–8 (HHV–8) as an inductive agent (necessary though not sufficient) in all epidemiologic subsets of the disease.²

There are 4 principal clinical variants of Kaposi’s sarcoma:

1. classic (or chronic),
2. African endemic (includes childhood lymphadenopathic),
3. transplant-associated, and
4. AIDS-related.

What you’ll see

Clinically, classic Kaposi’s sarcoma often first manifests as blue-red, well-demarcated, painless macules confined to the distal lower extremities.³ These slow-growing lesions may enlarge to forms papules and plaques, or progress to nodules and tumors. Unilateral involvement is often observed at the outset of the disease, with potential centripetal spread occurring late-in-course.³

Early lesions are generally soft, spongy, and “angiomatous,” while in the advanced state, lesional skin becomes hard, solid, and brown in color.³ Edema of the surrounding tissue is common. In addition to the skin, classic Kaposi’s sarcoma also involves mucosal sites (especially the oral and gastrointestinal mucosae).

Differential includes melanocytic nevus

A differential diagnosis for classic Kaposi’s sarcoma includes stasis dermatitis (“acroangiodermatitis”), melanocytic nevus, pyogenic granuloma, hemangioma, granuloma annulare, arthropod assault, and dermatofibroma/dermatofibrosarcoma protuberans (DF/DFSP).

Melanocytic nevi, pyogenic granuloma, hemangioma, granuloma annulare, and DF/DFSP ordinarily feature single lesions, while Kaposi’s sarcoma has multiple lesions. An arthropod assault is pruritic, and stasis dermatitis typically has dilated/varicose veins.