Sporotrichosis

An infection caused by the saprophytic fungus Sporothrix schenckii, usually initiated at cutaneous sites of trauma that spreads via lymphatics to form nodules that break down into abscesses and ulcers if untreated. S. schenckii is found on rose or barberry bushes and sphagnum moss or other mulches. Horticulturists, gardeners, farm laborers, and timber workers are most often infected.

Symptoms and Signs

Lymphocutaneous infections are most common. They can occur on any body site but characteristically involve one hand and arm, although primary lesions may occur on exposed surfaces of the feet or face. Occasionally, without primary lymphocutaneous lesions, the lungs are involved or hematogenous spread leads to involvement of other sites, especially peripheral joints.

A primary lesion may appear as a small, nontender papule or, occasionally, as a slowly expanding subcutaneous nodule that eventually becomes necrotic and sometimes ulcerates. Typically, a few days or weeks later, a chain of draining lymph nodes begins to enlarge slowly but progressively, forming movable subcutaneous nodules. If untreated, overlying skin reddens and may later necrose, sometimes causing an abscess, ulceration, and bacterial superinfection. Systemic signs and symptoms of infection are notably absent.

Lymphocutaneous lesions seldom, if ever, lead to hematogenous dissemination to other sites. However, rare cases of dissemination do occur, usually causing indolent infections of multiple peripheral joints, sometimes bones, and, less often, genitalia, liver, spleen, kidney, or meninges. Inhalation of spores causes chronic pneumonia, manifested by localized infiltrates or cavities, most often in patients with preexisting chronic lung disease.

Diagnosis, Prognosis, and Treatment

The illness must be differentiated from local infections caused by Mycobacterium tuberculosis, atypical mycobacteria, Nocardia, or other organisms. Culture from the active infection site provides the definitive diagnosis. S. schenckii yeasts can be seen only rarely in fixed tissue specimens, even with special staining. Serologic tests are not widely available. Delay in proper treatment commonly occurs because, during the early, nondisseminated stage, the primary lesion is misdiagnosed as a spider bite, especially in regions known to be infested with spider species that cause necrotic arachnidism.

Lymphocutaneous sporotrichosis is chronic and indolent, but potentially fatal only if bacterial superinfections cause sepsis. Oral itraconazole is the treatment of choice, replacing prolonged administration of saturated solution of potassium iodide, which is less effective and causes troubling toxic effects far more frequently. IV amphotericin B has been successful in clearing most systemic cases, but relapses are frequent. Itraconazole may prove to be more effective, but experience is limited.

Author: Carolyn Willbanks