AESOP syndrome is a rare paraneoplastic syndrome associated with an underlying plasma cell disorder. AESOP comprises adenopathy and an extensive skin patch overlying a plasmacytoma. The plasmacytoma may be solitary, or it may be associated with POEMS syndrome (polyneuropathy, organomegaly, endocrinopathy, monoclonal protein, skin changes) or Castleman disease. There have been no reported cases of associated myeloma. A single case of AESOP occurring in the setting of a Ewing sarcoma-like small blue cell malignant neoplasm has been reported.

AESOP is extremely rare. It has been diagnosed primarily in men of Northern European descent in their fourth to eighth decade of life. The characteristic skin finding is a large red to violaceous blanchable patch or thin plaque that expands slowly over months to years without associated pain or pruritus. Among reported cases, the patch or plaque measured 7-20 cm and rate of growth averaged 5-10 cm per year. The patch always overlies bone, typically the ribs or sternum, though it has been seen over the clavicle, scapula, and skull.

Patients typically have unilateral or bilateral enlarged, firm, and mobile regional lymph nodes in the axillary, supraclavicular, or cervical areas. Mediastinal lymphadenopathy may be revealed once imaging studies are performed. A palpable bony mass is often not apparent at presentation but becomes evident over time and may be associated with bone pain.

The skin findings of AESOP are thought to be caused by diffusion of local angiogenic and growth-promoting cytokines from the underlying malignancy to the skin. This triggers an increase in the vascularity of the dermis.