Signalment:
9 year MC Lab X Weight = 35kg

History, Presenting Complaint:
2-3 week history of polyuria and polydipsia
Indoor dog 1 other healthy dog.
Current vaccines, no other signs of illness (no V/D/C/S)….
Good appetite, normal activity

Physical Examination:
All systems were assessed and were within normal limits.

Problem List:
Polyuria and polydipsia

Rule Out List:

• Renal failure
• Endocrine disorders (hyperadrenocorticism, hypoadrenocorticism, diabetes mellitus)
• Pyelonephritis
• Hepatic disease
• Electrolyte abnormalities (hypercalcemia, hypokalemia)
• Renal medullary solute washout
• Medication (prednisone, diuretics)
• Diabetes insipidus (nephrogenic and central)
• Primary renal glucosuria
• Neoplastic disorders

Diagnostics:
A complete blood count (CBC), biochemical profile, urinalysis, and urine culture were obtained.
The CBC was within normal limits. Biochemical profile was within normal limits with the exception of an elevated BUN of 43 (normal 7-27), and an elevated globulin of 5.0 (normal 2.8-4.5). Urinalysis confirmed polydipsia with a specific gravity of 1.005 in an otherwise benign sediment. Urine culture was negative.
Thoracic and abdominal radiographs were performed. Results were within normal limits.

An ACTH stimulation test was performed to rule out hyperadrenocorticism Results were within normal limits.
Pre Cortisol 3.1 ug/dl
Post Cortisol 12.9 ug/dl

Bile acids were performed to rule out an underlying hepatopathy. Results were within normal limits.
Pre 1.5 Umol/L
Post 4.0 Umol/L

Updated problem list:
(1) Polyuria and polydipsia
(2) Elevated BUN
(3) Hyperglobulinemia

(1) Polyuria and polydipsia
Renal failure
Pyelonephritis (less likely with negative urine culture)
Hepatic disease (less likely with normal bile acids)
Renal medullary solute washout
Diabetes insipidus (nephrogenic and central)
Neoplastic disorders

(2) Elevated BUN:
Renal disease
GI bleeding

(3) Hyperglobulinemia

Polyclonal Gammopathy:
Chronic infectious disease (bacteria, fungal, protozoal, rickettsial, and viral)
Neoplasia
Autoimmune disorders

Monoclonal Gammopathy:
Neoplasia (multiple myeloma, lymphosarcoma)
Inflammation/infection (Ehrlichiosis)
Idiopathic (Waldenstrom macroglobulinemia)

Diagnostics:
An abdominal ultrasound, tick titers, and a protein electrophoresis were performed.

Abdominal ultrasound was within normal limits with the exception of a mildly enlarged, uniform spleen. Several aspirates were obtained and submitted for cytology.

Tick titers for Ehrlichia Canis, Lyme disease, and Rocky Mountain spotted fever were negative.

Protein electrophoresis was consistent with a monoclonal gammopathy

Splenic cytology confirmed a plasma cell tumor.

A urine sample was submitted for Bence Jones proteins, and was positive.

A bone marrow aspirate was performed and was within normal limits.

A diagnosis of multiple myeloma was made.

Multiple myeloma is a malignant neoplasm of hematopoietic tissue derived from a monoclonal population of plasma cells in bone marrow.
Two of four defining features must be present for diagnosis--monoclonal gammopathy, bone marrow invasion by plasma cells, Bence Jones proteinuria, and lytic bone lesions. This patient had a monoclonal gammopathy, plasma cell infiltrate of the spleen, and was positive for Bence Jones proteins.

Historical and clinical signs depend on location and extent of disease. Lameness/bone pain, blindness, epistaxis, dementia, and general lethargy are the most common findings. This patient presented with only polyuria and polydipsia, likely secondary to nephrotoxicity, either secondary to protein deposition of amyloid or direct effect of the protein on renal tubules.

Chemotherapy is palliative, but long remissions are possible.
This patient was started on a protocol of melphalan and prednisone.
CBC and platelet counts were followed weekly for 4 weeks, and then monthly thereafter.