Silver stain highlights infection of the dermis by fungal elements morphologically compatible but not diagnostic for Sporothrix. The culture confirmed the diagnosis.
The epithelium is less involved, but there are numerous fungal elements and neutrophils in the underlying dermis.
Sporothrix schenckii, a fungus found in sphagnum moss, hay, in other plant materials, and in the soil, is the etiological agent. Small cuts or punctures in the skin occuring from thorns, barbs, pine needles, or wires allow access of the fungus. It can also be inhaled and cause pulmonary infection, but it does not spread from person to person. However, handling of infected cats may potentially be infectious.
Initially a small painless bump, usually on the finger, hand or arm, arises, and it often resembles an insect bite. The nodule may develop between 1-12 weeks after exposure. Later additional nodules develop, which open and may resemble boils. Eventually the nodules ulcerate, and are slow to heal. If untreated, the infection spreads along lymphocutaneous routes. Pneumonia rarely occurs from fungal spore inhalation, and it may potentially disseminate to other sites such as the joints and the central nervous system.
Swab culture allows for proper diagnosis. Treatment with saturated potassium iodide solution or itraconazole is preferred for cutaneous disease. Itraconazole is used for lymphocutaneous sporotrichosis, as well as bone and joint infections. Further disseminated disease or CNS involvement is usually treated with Amphotericin.
(1)Pathology of the Skin
*Slide material courtesy of Dr. Lida Crooks, Veterans Affairs Hospital, Albuquerque NM