- Staphylococcus aureus
- Streptococcal species
- Gram-negative bacteria (especially post-surgical)
- Oral flora, including anaerobes (if evolved from esophageal perforation or deep space cervical infections)
- Candida species (rare)
- Histoplasma capsulatum (most common)
- Mycobacterium tuberculosis
- Coccidioides immitis
- Wucheria bancrofti
- This may also be due to noninfectious etiologies.
- Rheumatoid arthritis
- IgG-4 disease
- ANCA-related vasculitis
- Drug therapy (methysergide)
- Idiopathic: if etiology is undetermined.
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