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Friday, December 5, 2008
Solution for case 5
Tentative diagnosis: Transmissible Venereal Tumor (TVT).
Differentials: Canine Herpesvirus, Lymphoma, or preputial blockage.
Further diagnostic tests: Fine needle aspirate to look at the cells of the lesion. 
After the aspirate was stained with Wright’s stain, large round cells with central nucleoli were seen. TVT is related to other round cell tumors such as a lymphoma or a mast cell tumor.  The round cell tumors appear microscopically as single cells, usually described as “discrete” because they are separate from each other.
Other diagnostic tests: Impression smear or biopsy of the lesion for histopathology
Transmissible Venereal Tumor is contracted through physical contact between animals.  They are found mostly on genitals, but also reported on nose, mouth, and anus.  The tumor presents as a cauliflower-like, pedunculated mass that is nodular in appearance, can often be ulcerated, inflamed and bleed easily.  Sometimes misdiagnosed as hematuria due to bloody discharge, which is why it is important to look closely at genitals and take appropriate samples.  TVT can initially grow quickly, but metastasis is uncommon (5%).    A complication of this tumor is urinary retention.  The urethra can be blocked and cause urine to retained in the body, which could lead to an acidosis.
On the top of our differential diagnosis list is Transmissible Venereal Tumor, but after that it was possible for this lesion to be Canine Herpesvirus, Lymphoma, or preputial blockage. 
Canine Herpesvirus could be ruled out because this is typically a disease of puppies less than 2-3 weeks old.  This virus is released in penile or vaginal secretions and could present as a raised sore on the penis, but this is very rare.  If it were, the most important thing to do immediately is to keep the pup warm as a low body temperature allows the virus to spread throughout the body. 
Lymphoma can be seen in extragenital lesions, but it could be ruled out after doing a fine needle aspirate of the lesion and due to the clinical signs.  A lymphoma or lymphosarcoma would show with enlarged lymph nodes and if a CBC would show a leukocytosis, along with the necrosis of the tumor inducing a neutrophilia.  Clinical signs would have been much more severe, affecting the spleen, liver or CNS.
Preputial blockage is a problem with intact males.  This is an accumulation of urine, secretions and debris in the prepuce which leads to infection and necrosis.  This could be ruled out because the lesion was on the penis and even if this infections spread to the penis, then necrosis would look black instead of fleshy and cauliflower-like. 
Treatment:
Vincristine sulfate was given weekly, while alternating the left and right cephalic veins.  After about 6 injections the lesions have been greatly reduced and once the tumor was resolved, one more injection was given. 
Vincristine is a mitotic inhibitor originally derived from the Vinca rosea plant.  It has an antineoplastic effect by disrupting and disassembling the microtubules in the cells.  It was given intravenously with a catheter in the left cephalic vein.  It was important that Vincristine is not administered perivascularly because it causes tissue sloughing.  It would cause such severe vesication and ulceration it could be so deep that tendons and bone would be exposed.  The other side effects of Vincristine are neurological. 
Doxorubicin is another chemotherapy drug used in the treatment of TVT.  This is an antineoplastic antibiotic, which destroys DNA.  Along with the similar side effect of myelosuppression, this drug can also cause perivascular sloughing as well as phlebitis and urticaria around injection site.   But the vesication caused by vincristine will eventually heal with proper bandaging while the damage done with Doxorubicin is beyond repair. Doxorubicin is cardio-toxic too.  
Surgery is not recommended for transmissible venereal tumors mostly due to the anatomic locations of the tumors.  It would be difficult to excise the lesions and ensure that the entire mass was removed.  Likelihood of recurrence is also more after surgery.

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posted by Dr Banga's Websites @ 12:00 AM  
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