Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (382 page)

   
Bone marrow biopsy and aspirate
are usually normal. They are necessary to rule out PCM.

   
Biopsy of SPB or EP
: Monoclonal plasma cells are seen. Some plasma cells can have plasmablastic or anaplastic morphology. EP cases might pose a diagnostic challenge, as they might be difficult to distinguish from lymphoplasmacytic lymphomas.

   
CBC
is usually normal.

   
Serum protein electrophoresis and immunofixation
may reveal a monoclonal protein (κ or λ) and identify a specific heavy chain (EP patients commonly have IgA).

   
Urine protein electrophoresis and immunofixation
may reveal M protein (BJ protein).

   
Serum free light chain ratio
is useful for predicting prognosis.

   
Renal function tests
may be abnormal in the presence of monoclonal light chain proteinuria.

   
Immunophenotype
is similar to that of PCM.

   
Cytogenetics
: Genetic abnormalities are similar to those described for PCM but are demonstrated infrequently.

Suggested Reading

Swerdlow SH, Campo E, Harris NL, et al.
WHO Classification of Tumours of Haematopoietic and Lymphoid Tissues
, 4th ed. Lyon, France: International Agency for Research on Cancer; 2008:208–209.

IMMUNOGLOBULIN LIGHT CHAIN AMYLOIDOSIS (ILCA)

   Definition

Amyloidosis is a heterogeneous group of diseases characterized by the deposition of amyloid fibrils in soft tissues. The fibrils are either intact or fragments of Ig light chains in the form of insoluble antiparallel β-pleated sheet configuration. More than 28 types of amyloid have been identified, all of which stain positively with Congo red. A previously used nomenclature consisted of three types of amyloidosis: primary, secondary, and hereditary. A new system uses an abbreviation of the native amyloid protein. For the practical purpose of this textbook, I will focus on ILCA (AL), previously referred as primary amyloidosis (PA). Genetic mutations often with an amino acid substitution can result in an amyloidogenic protein. Secondary amyloidosis (AA amyloidosis) can be seen with prolonged inflammatory conditions and infections, including transmission by prions, and in familial periodic fever. Another form of amyloidosis is seen in Alzheimer disease where the amyloid fibrils are present exclusively in the central nervous system.

   PA occurs in the setting of plasma cell dyscrasias—MGUS and PCM or lymphoplasmacytic lymphoma. Currently, it is also classified as amyloidosis-AL (associated with light chain) type, which should be differentiated from secondary amyloidosis or amyloidosis-AA type. Light chain deposition disease (LCDD) is a different entity characterized by deposition of light chains without formation of amyloid β sheets.

   Who Should Be Suspected?