Veterinary Guide to Hyperviscosity Syndrome in Dogs 2025 ⚕️🐾

By Dr. Duncan Houston BVSc

🩺 What Is Hyperviscosity Syndrome?

Hyperviscosity syndrome (HVS) in dogs is a condition where the blood becomes abnormally "thick"—usually due to excessive plasma proteins, often from monoclonal gammopathies like multiple myeloma—or, less commonly, high red cell mass. This results in sludging through small vessels, impaired circulation, coagulopathy, and multi-system effects.

🧬 Causes & Underlying Conditions

Monoclonal gammopathies: plasma cell tumors (e.g., multiple myeloma), Waldenström-type syndromes, IgM/IgA excess.
Lymphoid cancers: lymphoma, leukemia with high WBC counts.
Polycythemia: elevated red cell mass rarely.
Chronic inflammation: autoimmune disorders or infections causing hyperglobulinemia.

👀 Clinical Signs: The Triad & More

The classic triad in HVS includes:

Neurologic symptoms: ataxia, disorientation, seizures.
Visual disturbances: retinal hemorrhage, detachment, dilated vessels.
Mucosal bleeding: nosebleeds, gum bleeding, coagulopathy.

Other symptoms include:

Anorexia, depression, lethargy, vomiting, diarrhea.
Polyuria/polydipsia and respiratory signs due to volume overload.
Tachycardia, congestive heart failure signs.

🔍 Diagnosis: Multi-Faceted Approach

Full blood panel: CBC, chemistry, urinalysis—look for total protein, globulins.
Protein electrophoresis: identifies monoclonal spikes.
Imaging and biopsy: confirms multiple myeloma or lymphoid tumors.
Ophthalmic exam: to assess retinal lesions.
Neurologic evaluation: to evaluate mental status and seizures.

🛠️ Treatment: Support & Targeted Therapy

▶️ Emergency Stabilization

IV fluids: restore circulation and reduce viscosity.
Oxygen therapy is needed for hypoxia.
Blood products: if coagulopathy is severe.

▶️ Plasmapheresis

For severe cases with neurologic or bleeding signs, plasmapheresis rapidly removes excess proteins. In one case, double-filtration treatments every week markedly reduced total protein and clinical signs in a dog with myeloma.

▶️ Specific Disease Therapy

Multiple myeloma: melphalan + prednisone, often with bisphosphonates for bone pain, achieving remissions in ~92% of dogs.
Lymphoma/leukemia: chemotherapy tailored to the disease.
Waldenström or IgM: immunochemotherapy; plasmapheresis may be repeated as needed.
Inflammatory causes: immunosuppressives or antibiotics as indicated.

📊 Monitoring & Prognosis

Lab checks: protein levels, CBC, chemistry during chemo cycles.
Eye & neurologic exams: monitor progression or improvement.
Medical imaging: to assess tumor/bone response.

Prognosis depends heavily on the underlying disease. Dogs with myeloma may have a median survival of 12–18 months; plasmapheresis offers short-term symptom relief, but disease-targeted therapy is key.

🏡 Owner Tips for Home Care

Provide a calm, low-stress environment; monitor neurologic and bleeding signs.
Track appetite, drinking, urination, coughing, and nasal discharge.
Ensure safety: non-slip flooring and close supervision.
Follow fluid, medication, and appointment schedules closely.
Prepare for potential repeat plasmapheresis sessions.

📱 Ask A Vet Ecosystem Support

Telehealth monitoring: track clinical signs and response to therapy remotely.
Strategic guidance on home phlebotomy scheduling and early signs to watch.

🎓 Case Highlight

A 12-year-old mixed-breed with confirmed multiple myeloma underwent serial plasmapheresis on days 0, 7, and 22, which significantly reduced protein levels and resolved neurologic signs, temporarily providing dramatic clinical improvement.

🔚 Final Takeaways

Hyperviscosity is a syndrome, not a diagnosis—treat the underlying disease.
Emergency care includes fluids, oxygen, and plasmapheresis as needed.
Long-term outcomes depend on cancer or inflammatory control.
Regular monitoring ensures early intervention for relapses or complications.
Ask A Vet is here to support every step—from diagnosis to home care and monitoring 🐶❤️.

Dr Duncan Houston BVSc, Ask A Vet founder. Download the Ask A Vet app for instant expert support—making thick blood easy to manage with confidence! 🐾