- Primary bone marrow problem→ polycythemia vera
- Secondary process→ testosterone supplementation, renal/liver/splenic cancer, inappropriate use of epo, chronic hypxemia, osa
- Hepatic vein or other venous clot in unusual location or otherwise unexplained
- Mesenteric ischemia
- Other arterial insufficiency from sludging
- Itching exacerbated by hot shower
- Sometimes bleeding