Feline hyperviscosity syndrome

© August, JR (2006) Consultations in Feline Internal Medicine, Vol 5.  Elsevier Saunders

Hyperviscosity syndrome (HVS) refers to a collection of clinical signs resulting from increased serum or whole blood viscosity. Serum viscosity is determined by the concentration, size and shape of serum proteins. In human beings, hyperviscosity is observed most often in Waldenstrom's macroglobulinemia with IgM, followed by IgA myeloma, as is least common in IgG myeloma. The most common cause of monoclonal hyperglobulinemia in cats is multiple myeloma. HVS also has been reported to occur secondary to lymphoma and an extramedullary plasmacytoma in cats. In contrast to human beings, IgG is the immunoglobulin responsible most often for multiple myeloma and HVS in cats.

Clinical signs

HVS usually manifests with circulatory problems secondary to sludging of blood leading to inadequate perfusion. Common organ systems affected by HVS include CNS, renal, cardiovascular and ophthalmic. Coagulation abnormalities also are common, and signs associated with coagulopathies often are secondary to platelet dysfunction including mucosal haemorrhage, melena, and ecchymoses. In one report of two cats with multiple myeloma and HVS, clinical signs included pale mucous membranes, dehydration, retinal haemorrhages, dilated and tortuous retinal vessels, seizures, head tilt, nystagmus, systolic murmur and a gallop rhythm.

Diagnosis

The diagnosis of HVS should be suspected in any cat with hyperglobulinemia and clinical signs related to the organ systems listed above. Patients with hyperglobulinemia should have a minimum database performed including a complete blood cell count, biochemistry and urinalysis. A serum electrophoresis is recommended to confirm the presence of a monoclonal gammopathy. The urine also should be screened for Bence-Jones proteins with a heat precipitation test. The serum viscosity can be determined using an Ostwald viscosimeter. Normal values for cats have been reported in two separate studies to be less than 2.5 and less than 1.7. A bone marrow aspirate also should be considered if a monoclonal gammopathy is present to aid in diagnosing multiple myeloma or lymphoma.

Treatment

The management of HVS involves treatment of the underlying disease and reduction of the serum viscosity. Chemotherapy is indicated to reduce the tumour volume in multiple myeloma and lymphoma. Plasmapheresis can be used to reduce the protein concentration but is not widely available in veterinary medicine. In the absence of the specialised equipment required for plasmapheresis, whole blood can be removed from the patient and separated into plasma and cells. The plasma subsequently is discarded and the cells are suspended in an equal volume of 0.9 per cent NaCl and administered intravenously to the patient. If dehydration or renal impairment is present, appropriate fluid diuresis may be beneficial. Patients with HVS also should be screened carefully for infection secondary to immunosuppression and treated appropriately with bactericidal antibiotics.