Sporotrichosis is an uncommon, chronic mycosis caused by Sporothrix schenckii. This ubiquitous plant saprophyte is a dimorphic fungus that grows as a mold at room temperature and as a yeast-like form in tissue. It is distributed worldwide and found most commonly both in warm, highly humid regions and in temperate climates.
PATHOGENESIS AND EPIDEMIOLOGY
Infection is characterized by isolated cutaneous or subcutaneous necrotizing nodules associated with the indolent development of suppurating nodules along the course of the proximal lymphatics. Extracutaneous and pulmonary forms of the disease occur infrequently. The histopathologic findings of primary cutaneous disease combine features of both granulomatous and pyogenic inflammation. Granulomatous lesions consist of aggregations of epithelioid histiocytes with central areas of necrosis and neutrophils or zones of Langhans giant cells associated with fibroblasts and lymphocytes. Occasionally, areas of microabscesses unassociated with granulomatous reaction may be seen. In chronic disease, pseudoepitheliomatous hyperplasia may be extensive and mimic neoplasm. A common histopathologic feature is the asteroid body, a round basophilic, yeast-like structure surrounded by rays of eosinophilic material thought to represent antigen-antibody complexes. The asteroid body may also be seen in other mycoses.
In 95% of cases, the organism is percutaneously inoculated by contaminated thorns, tree bark, splinters, or animal bites or scratches, especially from cats. Handling of contaminated plant material such as hay or moss also can lead to infection. Rare cases of human-to-human transmission have been reported. Sporotrichosis has been reported in many areas of the United States but is most common along the Mississippi River Valley and in the Plains states. Most cases are sporadic, but single-source outbreaks occur. Infection occurs in all age groups; about 10% to 25% of cases occur in children.
The spectrum of clinical findings in sporotrichosis can be divided into lymphocutaneous, fixed cutaneous, mucosal, extracutaneous (localized or multifocal), and pulmonary. Lymphocutaneous sporotrichosis accounts for 75% of infections. Following inoculation, the average incubation period is 3 weeks but ranges from 5 days to 6 months. Lesions usually involve the upper extremities but may occur on the face and trunk. The primary lesion is a firm, mobile, nontender subcutaneous nodule that enlarges and becomes discolored (Fig. 298-1). After 2 weeks, it undergoes necrosis, leaving a painless ulcer. During the next several weeks, additional lesions develop along the proximal lymphatics; intervening lymphatic channels become thickened, with overlying cutaneous erythema (Fig. 298-2). Lesions can persist for months to years. Few heal spontaneously, with scarring of the ulcers. Systemic symptoms are absent or mild.
The ulcer and surrounding erythema of fixed cutaneous sporotrichosis could be confused with a brown recluse spider bite. (Reproduced with permission from Knoop KJ, Stack LB, Storrow AB, et al: The Atlas of Emergency Medicine, 3rd ed. New York: McGraw-Hill; 2010. Photo contributor: Edward J. Otten, MD.)