What is the diagnosis and treatment for a patient with a chronic pustular rash, initially presenting as a round scaly rash with a fungal appearance, and multiple localized pustular eruptions, who works with cows and may be at risk for zoonotic infections?

Diagnosis and Management of Chronic Pustular Rash in a Cattle Worker

Most Likely Diagnosis: Sporotrichosis

Given the occupational exposure to cattle, initial fungal-appearing round scaly lesion that evolved into chronic pustular eruptions, the most likely diagnosis is sporotrichosis—a zoonotic fungal infection transmitted through traumatic inoculation from contaminated organic material or direct animal contact. 1

Key Diagnostic Features Supporting Sporotrichosis

• Occupational risk: Cattle workers have direct exposure to Sporothrix schenckii, which exists in decaying vegetation, soil, and can be transmitted through scratches from infected animals 1
• Clinical evolution: The progression from a round scaly lesion (mimicking dermatophytosis) to multiple localized pustular eruptions is characteristic of sporotrichosis 1
• Chronic nature: Sporotrichosis presents as a subacute-to-chronic infection, distinguishing it from acute bacterial processes 1

Immediate Diagnostic Workup Required

Obtain tissue for culture and histopathology immediately, as culture is the most sensitive diagnostic method for sporotrichosis. 1

• Culture: Aspirate or biopsy material from lesions should be inoculated on Sabouraud dextrose agar and incubated at room temperature 1
• Histopathology: Look for ovoid yeast cells (3-5 μm diameter, oval to cigar-shaped) with possible eosinophilic projections (asteroid bodies), though histopathology is often negative due to low organism burden 1
• Important caveat: Cultures may be negative despite active infection, so clinical suspicion should guide treatment decisions 1

Alternative Diagnoses to Consider

Zoophilic Dermatophytosis

• Trichophyton verrucosum causes ringworm in cattle and can produce highly inflammatory lesions in humans with occupational exposure 2, 3
• Trichophyton mentagrophytes (zoophilic strains) from farm animals can cause pustular dermatophytosis 2, 3
• Key distinguishing feature: True dermatophytosis typically remains scaly rather than evolving into multiple pustular eruptions 4, 5

Bacterial Superinfection of Dermatophytosis

• Zoophilic dermatophytes often cause highly inflammatory reactions that can become secondarily infected 2, 3
• However, the chronic nature and multiple localized pustular pattern favors a primary fungal process like sporotrichosis 1

Definitive Treatment Recommendations

For cutaneous and lymphocutaneous sporotrichosis, initiate itraconazole 200 mg orally daily for 3-6 months (continuing 2-4 weeks after all lesions resolve). 1

Treatment Algorithm:

First-line therapy:

• Itraconazole 200 mg daily demonstrates 80-100% response rates for cutaneous sporotrichosis 1
• Treatment duration: 3-6 months total, or 2-4 weeks after complete lesion resolution 1

Alternative therapy if itraconazole fails or is contraindicated:

• Trimethoprim-sulfamethoxazole for 18-24 months (though significantly inferior to itraconazole with only 51.3% success rate versus 86.4% for itraconazole) 1

For severe or disseminated disease:

• Amphotericin B induction therapy for 2-4 weeks, followed by itraconazole 200-400 mg daily 1

Critical Management Considerations

If Dermatophytosis is Confirmed Instead:

Treat with itraconazole 200 mg daily for 6-12 weeks for inflammatory zoophilic dermatophytosis. 1

• Essential infection control: Identify and treat the infected cattle source to prevent reinfection 3, 6
• Environmental decontamination: Disinfect the animal's environment, as zoophilic dermatophyte spores can persist for years 4, 3
• Screen contacts: Examine other farm workers and family members for infection 3

Common Pitfalls to Avoid:

• Do not dismiss sporotrichosis based on negative histopathology alone—culture is more sensitive 1
• Do not use topical antifungals alone for sporotrichosis or extensive zoophilic dermatophytosis—systemic therapy is required 1
• Do not overlook the animal source: Failure to identify and treat infected cattle will result in reinfection 3, 6
• Do not confuse with drug-induced pustular eruptions: The occupational context and initial fungal appearance make this unlikely 1

Expected Clinical Response

• Sporotrichosis: Clinical improvement should be evident within 4-8 weeks of initiating itraconazole, with complete resolution by 3-6 months 1
• Monitor for treatment failure: If no improvement occurs within 8 weeks, consider culture resistance testing or alternative diagnosis 1