Clinical Case Challenge

Cranial Mediastinal Mass in an Old Dog

History: An 11 year-old, spayed female Labrador retriever presents for polyuria and polydipsia.  The owners report mild lethargy but the dog is otherwise doing well.  Physical examination reveals body condition 4/9 but is otherwise within normal limits for a dog of this age. A complete blood count is within normal limits.  The chemistry profile reveals total calcium 15.4 mg/dl (NR,  9.4-11.8), ionized calcium 1.7 mmol/L (NR, 1.12-1.40), creatinine  2.1 mg/dl (NR, 0.6-2.0), BUN 39 mg/dl (NR, 8-30).  Urinalysis reveals dilute urine with a specific gravity of 1.008.   Thoracic radiographs are taken (Figure 1) and an ultrasound-guided fine needle aspiration is performed..

Figure 1: Lateral thoracic radiograph demonstrating cranial mediastinal mass.

What are the differential diagnoses for this lesion?

Figure 2: Cytology of cranial mediastinal mass. Green arrows point to mast cells.

What is your diagnosis?  How would you treat this dog? Continue reading

Current Concepts

Lymphoma in Dogs & Cats

Every veterinary student knows that lymphoma is the most common hematopoietic neoplasm in dogs and cats.  However, we are now recognizing that lymphoma isn’t a single clinical entity.  Rather, it is a collection of neoplastic disorders triggered by a myriad of genetic mutations and epigenetic factors that culminate in uncontrolled proliferation of lymphocytes.  Multi-institutional collaborative efforts are underway to illuminate the molecular fingerprints of canine and feline lymphomas that will allow for better understanding of the biology of lymphoma as well as improving treatment strategies and outcomes.  These benefits are likely to extend across species – even to humans as the field of comparative oncology grows.

Presentation of canine lymphoma

Figure 1. Lymphoma in dogs typically presents as generalized peripheral lymphadenopathy. Mandibular swelling due to lymph node enlargement, as shown here, often is a sign that leads clients to seek evaluation.

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Innovation

High-Dose Cyclophosphamide Holds Promise for Dogs with Lymphoma

For decades, the cornerstone of treatment for dogs with lymphoma has been chemotherapy employing five drugs: cyclophosphamide, doxorubicin, vincristine, L-asparaginase and prednisone.  Efforts to optimize these protocols by adjusting the doses and scheduling of drugs have not yielded significant improvement in remission rates or survival times.  In addition, the realization that discontinuous short chemotherapy protocols are as effective as traditional long protocols that include a lengthy maintenance phase has provided the opportunity to search for novel therapies to combat lymphoma before overt chemotherapy resistance develops.

Alternative modalities that have been studied include radiation therapy, chemotherapy agents traditionally reserved for rescue therapy, monoclonal antibodies, dose-intensified chemotherapy and bone marrow transplantation.  These approaches have yielded variable results, and some promising findings are under continued investigation. Continue reading