| Infections (active or postinfectious) |
| Viral (VZV, HIV, EBV, CMV, JCV, HBV, HCV) |
| Bacterial (Mycobacterium tuberculosis, Mycoplasma pneumonia, Streptococcus pneumoniae) |
| Fungal (Aspergillus spp, Candida albicans, Actinomyces spp) |
| Systemic rheumatic diseases |
| Systemic lupus erythematosus (SLE) |
| ANCA-associated vasculitis |
| Scleroderma |
| Dermatomyositis |
| Behçet disease |
| Systemic inflammatory diseases |
| Inflammatory bowel diseases |
| Hemophagocytic lymphohistiocytosis |
| Kawasaki disease |
| Other systemic conditions or exposures |
| Graft-versus-host disease (GVHD) |
| Radiation-induced |
| Drugs (cocaine, amphetamines) |
| Malignancies |
