Which is more likely to cause mucous membrane involvement, histoplasmosis or blastomycosis?

Blastomycosis Is More Likely to Cause Mucous Membrane Involvement Than Histoplasmosis

Blastomycosis has a higher propensity for causing mucous membrane involvement compared to histoplasmosis, particularly in its extrapulmonary manifestations. This distinction is important for clinicians to recognize when evaluating patients with suspected fungal infections.

Epidemiology and Clinical Presentation

Blastomycosis and histoplasmosis are both endemic fungal infections caused by dimorphic fungi:

• Blastomycosis (caused by Blastomyces dermatitidis):

  • Endemic to southeastern and south central states bordering the Mississippi and Ohio Rivers, midwestern states and Canadian provinces bordering the Great Lakes 1
  • Extrapulmonary disease occurs in 25-40% of patients with chronic blastomycosis 1
  • Skin is the most common extrapulmonary site, followed by bone, genitourinary system, and CNS 2

• Histoplasmosis (caused by Histoplasma capsulatum):

  • Similar endemic regions but with different patterns of dissemination
  • Less commonly involves mucous membranes in immunocompetent hosts

Evidence for Mucous Membrane Involvement

Blastomycosis:

• Extrapulmonary manifestations of blastomycosis frequently involve mucous membranes, particularly in the oropharynx, larynx, and genitourinary tract
• The skin and mucous membranes are primary sites of extrapulmonary disease in blastomycosis 1
• Blastomycosis has a particular tropism for skin and mucous membranes that is not seen to the same extent with histoplasmosis 2

Histoplasmosis:

• While histoplasmosis can disseminate, it less commonly involves mucous membranes compared to blastomycosis
• Histoplasmosis tends to involve the reticuloendothelial system (liver, spleen, lymph nodes) more than mucous membranes when it disseminates 2

Diagnostic Considerations

When evaluating patients with suspected mucous membrane involvement:

1. Consider blastomycosis first in patients with:

   • Oral or oropharyngeal lesions
   • Laryngeal lesions
   • Genital or urinary tract involvement
   • Cutaneous lesions with adjacent mucous membrane involvement

2. Diagnostic approach:

   • Direct visualization of organisms in cytologic and histologic specimens (sensitivity 50-90%) 1
   • Culture from respiratory specimens (sensitivity up to 86% across multiple specimens) 1
   • Blastomyces antigen testing in urine (sensitivity 92.9%, but cross-reactivity with histoplasmosis) 1
   • Serum antibody testing using EIA (sensitivity 87.8%) 1

Clinical Implications

The higher propensity of blastomycosis to involve mucous membranes has important implications:

1. When evaluating patients with mucous membrane lesions in endemic areas, blastomycosis should be higher on the differential diagnosis than histoplasmosis

2. Treatment considerations:

   • For non-life-threatening blastomycosis with mucous membrane involvement, itraconazole 200 mg twice daily for 6-12 months is the recommended therapy 1
   • For severe disease, lipid formulation amphotericin B (3-5 mg/kg/day) or amphotericin B deoxycholate (0.7-1 mg/kg/day) for 1-2 weeks followed by itraconazole is recommended 1

3. Monitoring:

   • Regular assessment of mucous membrane lesions for response to therapy
   • Follow-up cultures and antigen testing to confirm clearance of infection

Understanding the different propensities of these fungi for mucous membrane involvement can help guide diagnostic workup and management decisions in patients presenting with suspicious lesions in endemic regions.