September 2009
Written by Peter M. Banks, M.D., Director of Hematopathology, Carolinas Medical Center, Charlotte, North Carolina.

Submitting Clinician
Bryan D. Blitstein, M.D., Charlotte Surgical Group, Charlotte, NC.

Diagnosis
Localized low grade lymphoplasmacytic lymphoma of extranodal soft tissues, with amyloid production, so-called "amyloidoma".

Clinical History
This 86 year old woman had long noticed a slowly expanding area of subcutaneous brawny density, leading to excision of a 3 cm poorly demarcated mass.

Microscopy
Conventionally stained slides show a subcutaneous process composed of a lymphoid infiltrate with associated sclerosis and some amorphous hypocellular matrix material (see Figure 1).

At higher magnification the cellular infiltrates can be seen to be a mixture of small lymphocytes and plasmacytoid cells, the latter associated with abundant globules of immunoglobulin (green arrows in Figure 2).

Ancillary Studies
Congo Red staining reveals orange patches of coloration in the amorphous matrix material, which, with crossed polarizing lenses, demonstrates bright green birefringence (see Figure 3).

In-situ hybridization stains for immunoglobulin light chain RNA shows striking selective expression of lambda throughout the cellular infiltrate (see Figure 4).
Immunohistochemical staining shows strong predominant expression of CD20 with effectively no staining for CD138 (see Figure 5).
Additional special study findings included coexpression of CD43 by the lymphoid infiltrate and a uniformly very low labeling with Ki-67.

Discussion
Amyloid is an insoluble protein polymer which may derive from diverse human polypeptide components (1).  In most cases the disease process is relatively disseminated, producing  disease manifestations according to critical organ involvement, e.g., heart, urinary bladder, kidneys, liver, etc.  However,  there are rare cases of localized, tumefactive amyloid deposition which have been given the name “amyloidoma”.  These may occur in diverse sites  on the basis of differing underlying processes, such as the pulmonary amyloidoma  associated with autoimmune disease described in  the December 2004 Case-of-the-month.

In this case there was only a modest giant cell reaction to the amyloid deposits, however, sometimes it is so pronounced as to obscure the underlying nature of the process (2).

Amyloidomas arising in soft tissues are rare and may be of either AA or AL type.  Those of AA type appear to be particularly favorable clinically (3).  Those cases of AL type may reflect a localized plasma cellular or lymphomatous process. In this case the absence of CD138 expression, in contrast to the strong CD20 staining, indicates a lymphoma.

References

1. Vrana JA, Gamez JD, Madden BJ, Theis JD, Bergen HR 3rd, Dogan A.
   Classification of amyloidosis by laser microdissection and mass spectrometry based proteomic analysis in clinical biopsy specimens.  Blood. 2009 Oct 1. [Epub ahead of print]
2. Mukhopadhyay S, Damron TA, Valente AL.
   Recurrent amyloidoma of soft tissue with exuberant giant cell reaction.  Arch Pathol Lab Med  2003; 127: 1609-1611.
3. Krishnan J, Chu WS, Elrod JP, Frizzera G.
   Tumoral presentation of amyloidosis (amyloidomas) in soft tissues. A report of 14 cases.  Am J Clin Pathol  1993; 100: 135-144.

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