Page 199 - The Netter Collection of Medical Illustrations - Integumentary System_ Volume 4 ( PDFDrive )

Plate 6-24 Infectious Diseases
SPOROTRICHOSIS

Sporothrix schenckii is an environmental fungus that is
capable of causing human disease after direct inocula-
tion into the skin. Inoculation is the cause of cutaneous
sporotrichosis, which is considered to be a subcutane-
ous mycosis. Unusual cases of inhalation sporotrichosis
have been described in the literature, as have cases
of central nervous system disease. These cases occur
almost exclusively in immunosuppressed hosts. Sporo-
trichosis has classically been associated with inoculation
after the prick from a rose plant. This is well reported;
the fungus can be isolated from rose plants but is also Lymphangitic spread of sporotrichosis
found on many other plants and in soil environments.
Clinical Findings: Gardeners, florists, and outdoor
enthusiasts are at highest risk for infection from S.
schenckii. These activities and occupations increase the
likelihood of contact with the soil fungus. The fungus
lives in the environment, and humans become infected
by direct implantation of the fungus into the skin.
Common methods of inoculation are the prick of a
thorn or an injury contaminated with soil or plant mate-
rial. Within a few days after entry into the skin, a papule
and then a pustule form at the site of inoculation.
Patients may initially be given an antibiotic in the belief
that they have a bacterial infection. Often, it is not until
the pustule ulcerates and develops into a larger plaque
that the diagnosis is suspected or considered. Once this
has occurred, the fungus enters the local lymphatics and
proceeds to migrate proximally. As the fungus travels
through the lymphatic system, it periodically causes
draining sinus tracts to the surface, which appear as
papules or nodules. This characteristic lymphangitic
spread, also called sporotrichoid spread, is seen in most
cases of cutaneous sporotrichosis.
Although a few other infections can manifest with
lymphangitic spread, its presence along with a history Sporothrix schenckii on Sabouraud plate
of trauma suggests an infection with sporotrichosis. If
lymphangitic spread is present, a skin biopsy and fungal,
bacterial, and atypical mycobacterium cultures should
be performed. Less commonly, solitary plaques of spo-
rotrichosis occur without any evidence of sporotrichoid
spread. The disease manifests as solitary, nonhealing, Begins as small nodule and
slowly enlarging plaques with various amounts of ulcer- spreads to hand, wrist, and forearm
ation and drainage. (even systemically). This and other
Pathogenesis: S. schenckii is a dimorphic soil fungus mycotic infections are diagnosed
found throughout the environment. S. schenckii causes with biopsy and culture.
human infection by direct implantation of the mold
form of the fungus into the skin. Once the fungus has
entered the human body, it transforms into its yeast
form in response to the stable temperature. Most infec-
tions stay localized in the skin. In rare cases of severe
immunosuppression, S. schenckii becomes disseminated;
this occurs most frequently in association with human
immunodeficiency virus infection.
Histology: Findings from skin biopsy specimens of
sporotrichosis are not diagnostic in many cases. The
presence of a granulomatous infiltrate is often the main
histological feature. The periodic acid–Schiff (PAS) Structural growth pattern of Sporothrix schenckii
stain and Gomori’s methenamine silver (GMS) stain are
two excellent stains that highlight the fungus and allow
the pathologist to more readily appreciate the few cigar-
shaped fungal elements that are present within the dense S. schenckii can be grown at 37°C, although it grows antifungal medications. Itraconazole has been the most
inflammation. Multiple fungal organisms are rarely much more slowly at that temperature. widely studied and used antifungal and is the preferred
seen; they are observed most frequently in patients with Treatment: Saturated solution of potassium iodide agent. All the azole antifungal agents inhibit the fungal
an underlying immunodeficiency. (SSKI) has been used for decades to treat cutaneous cytochrome P450 enzyme 14-α-sterol-demethylase
S. schenckii is best cultured on Sabouraud’s media infections with S. schenckii. This medication has (CYP51A1). This inhibition prevents the fungus from
at room temperature. In these conditions, a white to an unknown mechanism of action in treating fungal producing ergosterol, a vital cell membrane compo-
brown colony of mold forms readily. As time elapses, infections, but it is believed to interrupt protein synthe- nent. Patients with pulmonary or central nervous
the fungus forms a brown pigment that turns the entire sis of the fungus and to boost local host immune func- system involvement or disseminated disease should be
colony brown to black. Because of its dimorphic nature, tion. The treatment of choice is one of the azole treated with amphotericin B.

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