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Plasma Cell Disorders
Orna Kristal, DVM, DACVIM (Oncology)

Kfar Saba, Israel

Etiology/Pathophysiology that precipitate in temperatures below 37 °C, so they are
usually lost in the clot when the blood is allowed to clot
Plasma cell neoplasms develop from clonal proliferation at room temperature.
of terminally differentiated immunoglobulin‐producing B Multiple myeloma negatively affects many organ
lymphocytes. They typically produce a homogenous systems as a result of tumor infiltration, high levels
monoclonal immunoglobulin which is why they are of circulating or deposited M component, production of
thought to originate from a single cell. However, not all cytokines by tumor cells or bone marrow microenviron­
neoplasms are secretory and some may be biclonal or ment and the effects on the immune system.
even polyclonal. Reported plasma cell disorders (PCD) in Abnormal immunoglobulins can lead to hyperviscos­
dogs and cats include multiple myeloma (MM), cutaneous ity syndrome (HVS) when high protein levels are reached.
and noncutaneous extramedullary plasmacytoma (EMP), The incidence of HVS is highest with IgM (WM) which
IgM (Waldenström) macroglobulinemia (WM), solitary is a pentamer and has a high molecular weight, followed
osseous plasmacytoma (SOP), and plasma cell leukemia. by IgA‐secreting myelomas which are dimers that can
The etiology of PCD in dogs and cats is largely unknown. polymerize. IgG‐associated HVS occurs less frequently.
No retroviral association was found in cats. Chronic Increased serum viscosity leads to “sludging” of blood in
immune stimulation in rodent models and chronic infec­ the vasculature that results in hypoxia and bleeding
tions in people have been associated with MM. Exposure diathesis leading to organ damage. HVS occurs in about
to ionizing radiation is a well‐known risk factor and agri­ 30% of dogs with MM and most commonly affects the
cultural chemicals, benzene, and petroleum products central nervous system (CNS), eyes, cardiovascular sys­
have been considered potential risk factors in humans. tem, and coagulation system.
Multiple myeloma usually originates from multiple Bleeding disorders are common in dogs with MM and
bone marrow sites in dogs. In cats, multicentric noncuta­ the mechanism is likely multifactorial. Coating of plate­
neous EMP with or without bone marrow involvement lets with paraproteins leads to decreased adhesiveness,
may present as MM. The neoplastic plasma cells in MM failure to release platelet factor III, and thrombocy­
typically secrete abnormal amounts of a single whole or topathia. Paraproteins can also interfere with clotting
partial (light or heavy chain) immunoglobulin called the factors and lead to abnormal fibrin polymerization.
M component, or paraprotein. In dogs, the M component Thrombocytopenia due to bone marrow infiltration
is usually IgA or IgG with similar frequency. In cats, the (myelophthisis) or immune‐mediated disease may also
IgG class is four times more common than IgA. IgM over­ contribute to bleeding. Approximately 33% of dogs and
production is uncommon in both species and is more 25% of cats with MM have clinical evidence of bleeding.
often associated with WM, a form of lymphoplasma­ Nonregenerative normocytic normochromic anemia
cytic lymphoma. The abnormal light chains are excreted is the most common hematologic abnormality in MM
in the urine and are called Bence Jones proteins. patients, present in about 66% of dogs and cats. Etiologies
Uncommon presentations in both species include may include myelophthisis, decreased erythrocyte life
biclonal gammopathies, nonsecretory MM, monoclonal span due to coating with paraprotein, blood loss, pro­
gammopathies without hyperglobulinemia and duction of inhibitory cytokines by myeloma cells and
cryoglobulinemia. Cryoglobulins are immunoglobulins decreased erythropoietin production due to renal

Clinical Small Animal Internal Medicine Volume II, First Edition. Edited by David S. Bruyette.
© 2020 John Wiley & Sons, Inc. Published 2020 by John Wiley & Sons, Inc.
Companion website: www.wiley.com/go/bruyette/clinical