Multiple myeloma is a systemic disease involving neoplastic proliferation of plasma cells. The bone marrow is the most common primary site, but other organs such as the gastrointestinal tract, liver, and spleen are also frequently involved. The secretory nature of the plasma cells can lead to many paraneoplastic conditions: hypercalcemia, hyperviscosity syndrome, and renal failure are the most common.
Hyperglobulinemia is the cause of the hyperviscosity syndrome. The size, shape, concentration, and degree of protein-protein interactions of the immunoglobulins affect the serum viscosity. Because of their size, IgM and IgA, are much more likely than IgG to cause the hyperviscosity.
The manifestations of hyperviscosity syndrome are varied, including: bleeding disorders, neurologic signs (coma, depression, dementia), congestive heart failure, and renal failure. Vision impairment may also be an initial presenting symptom.
Ocular lesions of hyperviscosity are related to its vascular manifestations: dilating retinal vessels, retinal hemorrhage and/or detachment, and optic disc swelling. Any of these may result in pupillary dilation and partial or complete vision impairment.
The pathophysiology of the retinopathy involves anemia, hemorrhagic diathesis, hypertension, tissue hypoxia, and vascular stasis. Anemia may be the result of bone marrow suppression or volume expansion induced by the high globulin concentration in the vascular space. The high concentrations of immunoglobulins may cause thrombocytopenia or platelet dysfunction resulting in hemorrhagic diathesis. Abnormalities in the clotting cascade and fibrin clot formation have also been seen with multiple myeloma.
Multiple myeloma and hyperviscosity syndrome are conditions which are responsive to treatment. If hyperviscosity is not severe, oral chemotherapy is the mainstay of therapy often giving survival times of 18 months or more with excellent quality of life. The two drugs most commonly utilized are melphalan and prednisone, although vincristine, cytoxan, and doxorubicin (Adriamycin) are used in refractory cases. If hyperviscosity is present, plasmapharesis is the immediate treatment of choice. This form of therapy rapidly reduces blood viscosity and allows the less rapidly acting chemotherapy to work. Aggressive diagnostics and treatment are often required to successfully treat animals with hyperviscosity syndrome. However, once the hyperviscosity is under control, the patient can then be managed with routine chemotherapy.
Acute blindness in a dog or cat with retinal lesions consistent with any or all of the abnormalities described above should prompt the search for systemic diseases including multiple myeloma. Unlike many neoplastic conditions, the treatment of multiple myeloma is generally affordable and of significant value in reducing patient morbidity.
Ocular Signs Associated with Multiple Myeloma
- Vision impairment/pupillary dilation
- Retinal detachment
- Retinal hemorrhages
- Papilledema/optic neuritis
Systemic Conditions Associated with Multiple Myeloma
- Systemic toxemia/septicemia
- Lyme disease
- Systemic hypertension
- Other disseminated neoplasia
This article was guest authored by Dr. Gerald Post, a board certified veterinary oncologist.