INTRODUCTION

Cutaneous sporotrichosis is an infection caused by the dimorphic fungus Sporothrix schenckii, which typically presents as pustules or erythematous papules in an ascending lymphatic (sporotrichoid) distribution. It classically occurs after puncture wound inoculation of foreign organic matter such as rose thorns. Herein, we present the case of a woman with sporotrichosis attributed to a cat scratch injury.

CASE PRESENTATION

An otherwise healthy 57-year-old woman presented to dermatology for a painful, poorly healing nodule of 7 months' duration in her left axilla. This initially appeared several weeks after sustaining multiple cat scratches at the site, which occurred while traveling in Asia. She completed 10 days of oral amoxicillin prescribed by her primary care physician, but new nodules continued appearing.

Physical examination revealed an afebrile well-appearing woman with a tender violaceous smooth linear plaque with central red crust and adjacent violaceous edematous papules confined to the left axilla (Figure 1). Two punch biopsies were sent for histology and tissue culture to evaluate for Bartonella henselae infection, and the patient was given oral cephalexin empirically.

FIGURE 1.:

Violaceous smooth linear plaque with central red crust and adjacent violaceous edematous papules.

Biopsy was notable for orthokeratosis overlying an unremarkable epidermis. There was underlying dermal fibrosis with hemorrhage of vertically oriented blood vessels and perivascular inflammation including plasma cells. Warthin–Starry and periodic acid–Schiff stains were negative. Tissue culture showed growth of S. schenckii, resulting in a diagnosis of cutaneous sporotrichosis.

She was prescribed oral itraconazole 100 mg twice daily. Upon follow-up 3 months later, she reported cessation of new lesions and improvement of the localized pain. She was instructed to continue itraconazole for 3 additional months as a precaution to prevent relapse.

DISCUSSION

Sporotrichosis is a subcutaneous mycosis acquired via puncture wound inoculation by thorns contaminated with S. schenckii (Sizar & Talati, 2022). Patients working outdoors are prone to contracting sporotrichosis through various foliage, particularly orchids and roses. Human infection from cats is also possible; sporotrichosis incidence in Brazil (where it is most often caused by S. brasiliensis) has recently increased 100-fold because of transmission from this vector (Elewski et al., 2018).

Sporotrichosis typically manifests as a single papule at the site of inoculation, and its progression depends on the host immune response. In naive hosts, attachment of regional lymphatics ensues, resulting in subcutaneous nodules and ulcers along the path of lymphatic drainage (Sizar & Talati, 2022). In patients previously exposed to Sporothrix, lymphatic spread does not occur, but a granulomatous plaque develops at the inoculation site (Elewski et al., 2018). Our patient's lesions were confined to the proximal arm without distal involvement, which is somewhat unusual. The subtle ascending lymphatic spread suggests this was her first exposure.

Histology of sporotrichosis typically shows granulomatous and suppurative inflammation in the dermis and subcutis (Elewski et al., 2018). Splendore–Hoeppli material or asteroid bodies can also be seen if yeast organisms are present, but this is not pathognomonic for sporotrichosis. S. schenckii may be evident as cigar-shaped yeast buds, highlighted by periodic acid–Schiff or silver stains. However, Sporothrix organisms are usually not seen on histopathology (or potassium hydroxide scrapings); thus, a culture is required to definitively diagnose sporotrichosis (Elewski et al., 2018; Sizar & Talati, 2022).

The differential diagnosis includes other localized eruptions with lymphangitic spread: Bartonella henselae, atypical mycobacteria, tuberculosis, nocardiosis, phaeohyphomycosis, leishmaniasis, anthrax, and tularemia (Elewski et al., 2018; Hasei et al., 2013; Sizar & Talati, 2022).

Topical treatment of sporotrichosis is not effective; first-line of treatment is itraconazole for 3–6 months (Sizar & Talati, 2022). Oral treatment with a saturated solution of potassium iodide has also been proven successful (Elewski et al., 2018). We report this case to promote timely recognition of sporotrichosis despite its sometimes variable presentation.

Acknowledgments

We are indebted to the patient, who graciously gave permission to publish this case and photograph.

REFERENCES Elewski B. E., Hughey L. C., Hunt K. M., Hay R. J. (2018). Fungal diseases. In J. L. Bolognia, J. V. Schaffer, L. Cerroni (Eds.), Dermatology (4th ed.).  Elsevier. Hasei M., Takeda K., Anzawa K., Nishibu A., Tanabe H., Mochizuki T. (2013). Case of phaeohyphomycosis producing sporotrichoid lesions. The Journal of Dermatology, 40(8), 638–640. https://doi.org/10.1111/1346-8138.12193 Sizar O., Talati R. (2022). Sporotrichosis. StatPearls Publishing. https://www.ncbi.nlm.nih.gov/books/NBK532255/