Question
Sporotrichosis.
Answer
Sporotrichosis is a chronic, subacute fungal infection caused by Sporothrix schenckii, a dimorphic fungus (mould in the environment/at room temperature, yeast form at body temperature in tissue) found in soil, decaying vegetation, and on plant material (thorns, rose bushes, sphagnum moss) — hence its classical epidemiological association with gardeners, farmers, and florists (“rose gardener’s disease”).
Transmission: traumatic inoculation of the organism into the skin, typically via a thorn prick, splinter, or other minor penetrating injury involving contaminated plant material.
Clinical form — lymphocutaneous sporotrichosis (the most common presentation): a painless nodule develops at the inoculation site (typically on a limb), which ulcerates; the infection then spreads proximally along lymphatic channels, producing a characteristic chain of secondary nodules along the course of lymphatic drainage, each of which can similarly ulcerate — this ascending, nodular lymphangitic spread pattern is highly characteristic and often clinically diagnostic.
Other clinical forms: fixed cutaneous sporotrichosis (localized, without lymphatic spread, more common in individuals with partial immunity); disseminated/systemic sporotrichosis (rare, in immunocompromised hosts, can involve bone, joints, lungs, or CNS).
Laboratory diagnosis: culture is the gold standard — grows as a mould at room temperature (25°C) on Sabouraud dextrose agar, and converts to a yeast form at 37°C, demonstrating the organism’s thermal dimorphism; direct microscopy of tissue is often unhelpful, since organisms are typically scanty in tissue (a recognized diagnostic challenge — biopsy may show only non-specific granulomatous inflammation); histopathology may occasionally reveal characteristic asteroid bodies (a yeast cell surrounded by a radiating eosinophilic (Splendore-Hoeppli) reaction).
Treatment: itraconazole is the treatment of choice for lymphocutaneous and cutaneous disease; saturated solution of potassium iodide (SSKI) is an older, effective, and inexpensive alternative; amphotericin B is reserved for severe/disseminated disease.