A. Infection

1. Viral: Cocksackie, Echovirus
2. Bacterial
3. Tuberculosis (especially in HIV+ patients)
4. Fungal - immunocompromised hosts

B. Malignancy

1. Lung
2. Breast
3. Lymphoma
4. Mesothelioma

C. Collagen Vascular Disease

1. Systemic Lupus Erythematosus
2. Rheumatoid Arthritis
3. Systemic Sclerosis