Page 1945 - Cote clinical veterinary advisor dogs and cats 4th

Thymoma 973

2
• Vincristine 0.02 mg/kg (or 0.5 mg/m • Avoid drugs that inhibit platelet function • Anecdotal reports suggest melatonin 3 mg
[pp. 607 and 609]) IV once weekly (author (e.g., NSAIDs). (<10 kg) or 6 mg (>10 kg) PO q 12h as
VetBooks.ir • Mycophenolate mofetil 10 mg/kg PO q 12h Possible Complications • Additional immunosuppressants (aza- Diseases and Disorders
adjunct therapy.
preference)
thioprine, cyclosporine, leflunomide) and/or
• Avoid cyclophosphamide in these patients;
(author preference)
hemorrhagic cystitis may be fatal.
• Red blood cell (RBC) transfusions (fresh
whole blood, packed cells) as needed • Glucocorticoid-induced side effects are splenectomy may be beneficial in refractory
cases. Consultation with an internal medicine
(p. 1169) common with long-term administration specialist is recommended.
• Platelet transfusions are usually impractical (polyuria, polydipsia, polyphagia; weight gain, • Many animals are euthanized due to adverse
because platelets are rapidly destroyed. panting, behavioral change, coat thinning, effects of glucocorticoids. Strategies to
○ Life-threatening, uncontrolled hemor- calcinosis cutis, and/or muscle weakness). decrease glucocorticoid-induced adverse
rhage may require platelet-rich plasma • Mycophenolate mofetil may cause diarrhea. effects include avoidance of obesity, use of
9
(6-12 mL/kg IV; >5 × 10 platelets/kg IV), an additional immunosuppressive agent to
frozen platelet concentrate, or lyophilized Recommended Monitoring lower glucocorticoid dosage, and routine
platelets (StablePlate RX). Platelet counts every other day until > 50,000/ monitoring for infections of the skin and
mcL, then weekly until normal urinary tract.
Chronic Treatment
• Discontinue vincristine after platelet count PROGNOSIS & OUTCOME Prevention
is > 50,000/mcL or if no response. • Future vaccinations should be limited to
• Taper prednisone/prednisolone and myco- • Prognosis is initially guarded, with fatal those considered essential.
phenolate after platelet count has normalized. bleeding into the brain or spinal cord • Stressful circumstances should be avoided
○ Decrease doses by 25%-50% every month possible. during severe thrombocytopenia to reduce
(in general) while monitoring platelet • Response often takes 3-10 days. the risk of self-trauma.
count. • After the platelet count normalizes, the
○ The minimum duration of therapy is prognosis is fair to good; survival rate is Technician Tips
typically 4-6 months. 84% for dogs treated at referral hospitals. Venipuncture should be performed with the
○ If the platelet count falls during the drug • Many pets are tapered completely from least possible trauma and pressure maintained
tapering, increase to the previous dose, immunosuppressive medications, although over the vein for a full 60 seconds. Venipuncture
and attempt to taper more slowly. relapse remains possible (10%-40% recur- from the jugular veins should be avoided.
○ Attempt to taper completely off predni- rence rate for dogs).
sone; treatment with mycophenolate alone Client Education
is used in patients requiring long-term PEARLS & CONSIDERATIONS • Frequent monitoring is necessary to
immunosuppression. prevent side effects of immunosuppressive
○ It may be preferable to allow mild Comments medications.
thrombocytopenia to persist to decrease • The presence of severe thrombocytopenia • Obesity must be prevented; body weight
medications to tolerable levels. (<25,000/mcL) in an otherwise healthy- should be carefully monitored.
appearing animal is most likely due to IMT.
Behavior/Exercise • If bleeding is present when the platelet count SUGGESTED READING
Activity and excitement should be minimized is > 25,000/mcL, an additional problem such O’Marra SK, et al: Treatment and predictors of
to avoid self-trauma until a safe platelet count as clotting factor deficiency, thrombocyto- outcome in dogs with immune-mediated thrombo-
(>25,000/mcL) is achieved. pathia, or vasculitis must be present. cytopenia. J Am Vet Med Assoc 238:346-352, 2011.
• Combination immunosuppressive therapy
Drug Interactions with mycophenolate mofetil is often more AUTHOR: Michael Stone, DVM, DACVIM
• Extravasation of vincristine causes severe skin effective and has fewer adverse effects than EDITOR: Jonathan E. Fogle DVM, PhD, DACVIM
necrosis; use an indwelling IV catheter. prednisone/prednisolone alone.

Thymoma Client Education
Sheet

BASIC INFORMATION GENETICS, BREED PREDISPOSITION • Megaesophagus (p. 642)
Dog: large-breed dogs (Labrador retriever, • Cardiac arrhythmias: rare
Definition German shepherd) may be more commonly • Cranial vena cava syndrome (p. 221): rare
A benign or malignant primary tumor in the affected. Clinical Presentation
cranial mediastinum that originates from the
thymic epithelium. The presenting complaints ASSOCIATED DISORDERS DISEASE FORMS/SUBTYPES
for animals with thymoma are signs caused by • Paraneoplastic syndromes associated with Epithelial cell–dominant, lymphocyte-dominant,
the space-occupying nature of the mediastinal thymoma and mixed forms exist and can make diagnosis
mass or paraneoplastic syndromes such as myas- ○ Myasthenia gravis (11%-50% of dogs with by fine-needle aspiration difficult.
thenia gravis, megaesophagus, or hypercalcemia. thymoma [p. 668])
○ Hypercalcemia (p. 491) HISTORY, CHIEF COMPLAINT
Epidemiology • Immune-mediated syndromes (less common) • Respiratory signs: very common chief
SPECIES, AGE, SEX ○ Polymyositis, dermatitis (e.g., feline complaints (tachypnea, dyspnea, coughing);
• Dog: average age is 8-10 years. thymoma-associated exfoliative dermati- signs may be surprisingly mild given size of
• Cat: average age is 9-12 years. tis), and myocarditis thymoma.

www.ExpertConsult.com