Multiple myeloma (extraosseous manifestations)

Extraosseous myeloma refers to any manifestation of multiple myeloma where there is plasma cell proliferation outside the skeleton. 

It is characterized by the ability of a clone and/or subclone to thrive and grow independent of the bone marrow microenvironment ¹².

Epidemiology

The overall incidence is thought to be ~10% (range 5-16%) of those diagnosed with myeloma ^3,7,8. It is considered to be more common in younger patients and in those with non-secretory myeloma and IgD myeloma ³.

Diagnosis

In most cases, especially patients with a coexisting malignancy, tissue diagnosis is often considered essential.

Pathology

This can potentially affect any organ system and the reported disease spectrum includes:

• reticuloendothelial system

  • lymph nodes (considered to be most common site ¹)

• central nervous system (CNS) involvement independent of bone is thought to occur in less than 1% of multiple myeloma ¹

  • leptomeningeal involvement: considered the commonest form of CNS involvement

• thorax

  • lung

    • pulmonary nodules

    • interstitial infiltrates

  • pleura

    • can manifest as a pleural effusion or pleural thickening

• abdomen

  • liver

    • thought to be most common solid organ involved in the abdomen ⁷

    • involvement of the liver can occur as diffuse sinusoidal infiltration or as distinct nodules

  • mesenteric: omental masses

  • pancreas

  • renal involvement

    • perirenal space: a relatively common occurrence in the abdomen ¹⁰

      • perirenal nodules: can mimic melanoma metastases ³

      • perirenal soft tissue thickening

    • intrarenal lesions

• other sites

  • subcutaneous tissues

  • skin

  • breast

  • testis ⁷

  • orbit ^5,6

Radiographic features 

Imaging features are non-specific and widely variable depending on the site. The condition can mimic other pathologies. When there is known background multiple myeloma, the development of focal soft tissue masses should be considered highly suspicious for extraosseous myeloma. In particular, the development of extraosseous soft tissue masses in a myeloma patient after stem cell transplantation should raise suspicion for extraosseous myeloma. It is important to know if there is more than one lesion.

Treatment and prognosis

The presence of extraosseous myeloma generally implies a poorer prognosis ³. More content required for treatment.

Differential diagnosis

Extraosseous myeloma can mimic a vast number of entities dependent on location. If there is only one lesion and the lesion reveals myelomatous / plasma cells on a biopsy, consider extramedullary plasmacytoma.