Medical Archive

Etiology

Histoplasmosis H.capsulatum
“Thick-walled spherules packed with endospores”

Epidemiology

Endemic to Ohio & Mississippi River valleys

Pathogenesis and pathology

1. Inhalation of bat/bird droppings
2. Converts to yeast form
3. Phagocytosed by alveolar macrophages – but macrophages cannot initially eliminate.
4. Replicate within macrophage and spread through the draining lymphatic system, RES
5. 2-4 weeks later…
   • Most healthy people (80%)
     • Cell-mediated immune response ? infection within granulomas
   • Minority
     • Develop self-limited pneumonia
   • Over time… 
     • The granulomas fibrose and calcify ? visualized on radiographic imaging
     • e.g., lungs, hilar and mediastinal LN, spleen.

Clinical manifestations

• Asymptomatic(80%)
• Pulmonary
  • Similar to Tb, mediastinal/hilar lymphadenopathy.
  • Arthralgias and erythema nodosum.
  • Infiltration of lymphocytes and monocytes
• Disseminated
  • Fever, fatigue, skin lesions, ulcerated lesions on the tongue.
  • Lymphadenopathy, pancytopenia, hepatosplenomegaly
  • As the organism targets histiocytes and the RES

Diagnosis

• Histoplasma antigen testing
  • Urine or blood
• Serology
  • Culture takes 3-4 weeks!

DTH. Found within macrophage.

Treatment

Disseminated histoplasmosis

• IV amphotericin B (fungicidal)
  • 1-2 weeks
• After 1-2 weeks of clinical improvement, most patients are switched to oral itraconazole (fungistatic)
  • ?1 year of maintenance therapy.