Page 1307 - Clinical Small Animal Internal Medicine

135 Plasma Cell Disorders 1245

differentiated and can be difficult to differentiate from therapy may be more suitable in cats with MM than
VetBooks.ir other round cell tumors. Immunohistochemistry (IHC) melphalan and responses have been documented.
Chlorambucil has been recommended for the treat­
is sometimes utilized in these cases to detect light and
heavy chains. The majority of EMPs stain for lambda
light‐chains, similar to the physiologic distribution of ment of WM at a dose of 0.2 mg/kg PO once daily,
although treatment with melphalan and prednisone may
light chains in normal canine and feline plasma cells. be effective as well.
Staining for multiple myeloma oncogene 1/interferon Rescue therapy after disease relapse may be attempted
regulatory factor 4 (MUM1/IRF4) is highly sensitive for with other alkylating agents including cyclophospha­
EMPs but 21% of B cell lymphomas stain positive as well. mide, chlorambucil, or CCNU. The VAD protocol which
It is therefore recommended to use it in combination includes vincristine, doxorubicin, and dexamethasone
with other round cell markers together with morphol­ has been extrapolated from humans, while others have
ogy of the cells. SOP, GI EMP, and multiple cutaneous used CHOP‐based lymphoma protocols. There are only
EMPs in dogs can metastasize, or develop into MM. anecdotal data regarding these rescue protocols, but it
Therefore, it is important to fully stage them at diagno­ appears that while response rate is quite high, most
sis. Staging includes SPE (even if total globulin level is responses are of short duration.
normal), bone marrow aspiration, survey skeletal radio­ Symptomatic animals presenting with severe compli­
graphs, and abdominal ultrasound. cations of MM require supportive care simultaneously
with diagnosis and initiation of antitumor therapy.
Animals with severe signs of HVS (altered mentation,
Therapy hemorrhage, retinal detachment, or CHF) can be treated
with plasmapharesis. Renal dysfunction, especially with
Chemotherapy with melphalan and prednisone is the concurrent hypercalcemia, is treated with IV fluid diure­
treatment of choice for MM in dogs. Although cure is sis until symptoms improve. Severe hypercalcemia can
unlikely, response to treatment is achieved in most dogs be treated with calcitonin in addition to fluid diuresis or
often for relatively long periods of time. Melphalan is with IV bisphosphonates if diagnosis is delayed.
prescribed at a dose of 0.1 mg/kg PO once daily for 10 Prednisone is highly effective in treating hypercalcemia
days, then 0.05 mg/kg PO once daily continuously. An but it should not be started prior to making a definitive
alternate pulse protocol with melphalan at 7 mg/m 2 diagnosis as it may obscure results. Hypercalcemia usu­
(rounded to the nearest whole 2 mg tablet) given once ally resolves quickly after starting chemotherapy. Dogs
daily for 5 days every 21 days is also used. Prednisone is with extensive lytic lesions should have exercise restric­
given at a dose of 0.5 mg/kg PO once daily for 10 days, tion and analgesia.
then 0.5 mg/kg PO on alternate days indefinitely or Bisphosphonates (BP) inhibit osteoclast activity and in
discontinued after 60 days. These protocols are usually human. They have been shown to reduce bone pain, the
well tolerated and the main toxicity of melphalan is mye­ incidence of pathologic fractures and prolong time to
losuppression, most commonly thrombocytopenia. first event. The more potent amino‐bisphosphonates
It is generally accepted that a reduction in serum levels such as pamidronate or zoledronate also appear to have
of the M component by at least 50% is a reasonable antitumor activity and zoledronate has shown a survival
therapeutic goal. In addition, clinical signs and clinical advantage over placebo and other BP in patients with
pathology abnormalities should also improve, usually symptomatic MM. Pamidronate or zoledronate probably
within 2–4 weeks. Radiographic improvement of skeletal have a role in the treatment of animals with osteolytic
lytic lesions may take several months, and may only be MM, but they have not yet been critically evaluated.
partial. Routine monitoring of response to treatment and Large lesions can be treated with radiation therapy
toxicity is usually done with a complete blood count (RT). In addition, fractures in weight‐bearing bones or
(CBC), total globulin level, and Bence Jones protein vertebrae require surgical stabilization alone or com­
(if originally present) every two weeks. A CBC should be bined with RT. Healing can occur, although it can be very
checked at least once on day 7 of the pulse protocol. slow and only if local tumor control is achieved. Patients
Once a good response is achieved and no cytopenias presenting with a fever, other evidence of infection, or
have been identified, follow‐up can be done less often. severe neutropenia should be treated with broad‐spec­
Melphalan and prednisone have also been used in cats trum antibiotics. Samples for culture and sensitivity
but melphalan is more myelosuppressive than in dogs, prior to antibiotic therapy should be collected if infec­
and may cause prolonged neutropenias. Ideally, melpha­ tion is suspected.
lan should be compounded for cats to allow accurate The treatment of choice for EMPs is usually surgical
dosing and avoid hazardous exposure of humans. Use of resection. The cutaneous and mucosal EMPs are usually
chlorambucil, cyclophosphamide, CCNU, or multidrug benign and complete surgical excision carries an