Dermatology Clinic CASE #1
Cutaneous Leishmaniasis
Leishmaniasis is a disease caused by intracellular protozoan parasites predominantly found in tropical areas of the world. Leishmania-like species have been discovered in amber dating back more than 100 million years.1 Archeologists discovered evidence of leishmaniasis in samples from Egyptian mummies as well as tablets from ancient Arabic societies.1 William Boog Leishman, a Scottish pathologist, discovered ovoid bodies in smears taken from the spleen of a soldier who died from emaciation and splenomegaly while in Calcutta, India, in 1900.1 Around the same time, Charles Donovan, a physician and professor of physiology, discovered similar ovoid bodies in splenic smears from Indian patients who had fever and splenomegaly.1 These 2 physicians are credited with the discovery of the parasite that causes visceral leishmaniasis.1 Leishmaniasis is categorized into 3 types: cutaneous, mucocutaneous, and visceral. Cutaneous leishmaniasis can be found in many places around the world, specifically in Latin America, Africa, Asia, and southern Europe. An estimated 350 million people are at risk for the disease; the worldwide prevalence is 12 million, with an annual incidence of cutaneous leishmaniasis of 1.5 million cases.2 The condition is particularly prevalent in the Middle East and North African countries, such as Afghanistan, Iran, Iraq, Morocco, Pakistan, Saudi Arabia, Sudan, Syria, and Yemen.3 Transmitted via an insect bite of infected female phlebotomine sand flies, leishmaniasis is caused by intracellular protozoan parasites of the genus Leishmania.4 Specifically, when a sand fly bites a host, it transmits the parasite in the promastigote form through its proboscis.These promastigotes are then phagocytosed by the host macrophages, transformed into amastigotes and multiply, and then spread to different tissues of the body. Sandflies can then have a blood meal on an infected host and become infected with amastigotes, which migrate to the gut of the sand fly to multiply. These amastigotes develop into promastigotes and then migrate to the sand fly’s proboscis to repeat the process when having a blood meal on the next host.4 The amastigotes within the macrophages are termed Leishman-Donovan bodies and can be visualized histologically.2 Initially, a wide variety of inflammatory cells are present at the site of infection. Histologic appearance of chronic lesions is characterized based on the strength of the immune
response of the host. If the immune response is sufficient, then epithelioid granulomata with few parasites are seen. If the immune response is poor, then a diffuse macrophage infiltrate with many parasites is seen.The immune response is T-cell-mediated, but the outcome differs in Th1 lymphocyte vs Th2 lymphocyte responses. Generally, the Th1 lymphocyte response leads to better outcomes.2,5 The cutaneous form of leishmaniasis is caused by approximately 14 different species of protozoa within the genus Leishmania, including L mexicana, L brasiliensis, L donovani, among others.2 Knowing the species of Leishmania that infected a patient can be useful because certain species are associated with prolonged, more severe courses of disease.
The differential diagnosis of leishmaniasis can be broad, primarily due to considerable variation in presentation of the lesions. Risk factors for cutaneous leishmaniasis include living in or visiting endemic regions or urban areas, warmer climate, environmental factors such as proximity of housing to dams and cowsheds, cracks in the walls of houses that encourage sand fly aggregation, and a suppressed immune system such as in individuals with HIV.6 Additionally, travelers and military personnel are at risk.7 Clinically, leishmaniasis appears initially as a small papule. If the lesion enlarges and develops an area of central necrosis, resembling the appearance of a volcano, then the lesion is termed a “wet” lesion.2,7 However, if the initial small papule either remains smooth or becomes hyperkeratotic, then the lesion is called a “dry” lesion.2,7 The outcome associated with a wet or a dry lesion can vary with different species of Leishmania.The edge of the lesion is thickened, and ulceration rarely extends into the subcutaneous tissue. Lesions develop on exposed areas of the skin where the sand fly can get access for a blood meal; however, satellite lesions may also develop due to the local spread of parasites. The size of the lesion is typically <5 cm in diameter but can reach up to 10 cm.2 The differential diagnosis of leishmaniasis can be broad, primarily due to considerable variation in presentation of the lesions. Several conditions that may mimic leishmaniasis include infected insect bites, ulceroglandular tularemia, cutaneous anthrax, cutaneous tuberculosis, and leprosy.2,7 It is also important to include noninfectious conditions such as basal cell carcinoma, squamous cell carcinoma, cutaneous lymphoma, and pyoderma gangrenosum within the differential.2,7
22 THE CLINICAL ADVISOR • JUNE 2020 • www.ClinicalAdvisor.com
