AMBULATORY PRACTICE


hypodermic needle may be placed percutaneously to identify the level of an identified rent.4 Openings to the urethral glands and bulbourethral glands are located proximal to the ischial arch. The pelvic urethra should be examined for signs of urethritis. The colliculus seminalis should be examined for dis- charge from the seminal vesicle or presence of any cystic structures.5 The seminal vesicles can be en- tered with the use of a sterile stylette and examined for purulent or hemorrhagic exudate. Transrectal massage of the seminal vesicles may elicit elimina- tion of accumulated fluid and may improve diagno- sis. Bacteriological samples may be obtained from the seminal vesicles or urethra. The bladder should be examined for cystitis or uroliths.


3. Differential Diagnoses and Treatment Options


Penile Neoplasia Squamous cell carcinoma (SCC) represents the ma- jority of diagnosed penile neoplasms. Hemosper- mia may occur as the result of ulceration of the glans or irritation of neoplastic tissues during erection. In a recent retrospective study of 3351 equine cuta- neous neoplasms, 18.9% were SCC, as were 57.8% of penile or preputial tumors. In another study, 74 of 114 (65%) of equine penile or preputial tumors were SCC. The mean age of affected horses ranged from 16.4 to 19.8 years.6,7 SCC is commonly identified in horses with unpigmented genitalia but can occur in any breed or color.7,8 Appaloosa and American Paint horses are significantly more affected than other breeds.7 Stallions appear to be less fre- quently affected than geldings, which may be a re- flection of the respective population sizes.9 The pathogenesis of penile SCC has been hypoth-


esized to result from infection with equine papillo- mavirus-2 (EcPV-2), which induces neoplastic changes in penile or preputial epithelium or existing papillomas.10,11 In 16 penile SCC, 15 were positive for EcPV-2 DNA as was a metastatic lymph node.12 Interestingly, 10% of healthy males were positive for EcPV-2 DNA in penile tissues, suggesting that some horses may be asymptomatic carriers.12 Other fac- tors relative to SCC formation include irritation of the skin by smegma or by ultraviolet sunlight expo- sure. The lesions are slow-growing, locally inva- sive, and metastasize late in disease to the inguinal lymph nodes. SCC which invade the cavernosus tissues of the penis may metastasize hematog- enously. Lesions are often not identified in non- breeding stallions until gross abnormalities are present, resulting in pain during collection, urina- tion, or masturbation; hemorrhage; or a foul odor. Early lesions may be raised, discolored, or ulcerated; later lesions may become granulomatous or “cauli- flower-like” in appearance. Large lesions may in- terfere with normal extension and retraction of the penis as well as urination. Treatment options for penile SCC depend on the size and character of the lesion as well as the pres-


42 2013  Vol. 59  AAEP PROCEEDINGS


ence of metastasis. Small lesions may be treated with chemotherapy, cryotherapy, or laser excision. Chemotherapy options include topical 5-fluorouracil (5-FU), intralesional cisplatin, or oral cyclooxygen- ase inhibitors. Five-fluorouracil, a fluorinated py- rimidine, is an anti-metabolite that blocks the methylation of deoxyuridic acid into thymidylic acid in the formation of DNA.13 Because thymidylic acid is high in SCC, 5-FU is thought to induce thy- midylate deficiency in the neoplastic cells, which leads to apoptosis; normal non-cancerous cells are not affected.13 A study of eight horses with penile or preputial SCC monitored the response to topical 5-FU after surgical debulking or as solitary treat- ment for small lesions.13 The treatment was applied immediately after surgery or the following day, after hemostasis had occurred, and additional treatments were performed at 14-day intervals until regression of the SCC. Thereafter, horses were evaluated and treated every 6 months to prevent remission. The mean number of treatments to achieve remission was five (range, two to seven), and all horses were still in remission 5 to 52 months later. Cisplatin, cis-diamminedichloroplatinum (II) or


CDDP, is a platinum-containing chemotherapy agent that binds and cross-links DNA to induce ap- optosis. It has been administered intratumorally to reduce the toxic systemic effects observed in some patients and to maximize tissue concentrations of this chemotherapeutic agent. Cisplatin in sesame oil emulsion was used to treat 151 SCC in 144 horses, either as solitary treatment or 10 to 14 days after surgery.14 Eighteen of these SCC were of male genital origin. Four treatments were admin- istered at 2-week intervals. The cure rate after one course of treatment was 88%.14 The use of cyclooxygenase (COX) inhibitors as che- motherapy agents has been researched in recent years. It has been demonstrated that COX is over- expressed in equine SCC and plays a role in cell growth and differentiation.15 Inhibition of COX-2 induces apopotosis in neoplastic cells by blocking prostaglandin E2 synthesis and therefore angiogen- esis and invasiveness.16 Elce et al16 demonstrated the expression of COX-1 and COX-2 proteins in tis- sue samples of four preputial and five penile SCC in horses. COX-2 expression was significantly in- creased in neoplastic versus non-neoplastic prepu- tial tissues (P  0.04).16 This study also suggested that COX expression in horses was not limited to SCC but also occurred in normal tissues, a finding unique to horses. Another study demonstrated ex- pression of COX-2 in 32 of 37 (86.5%) equine SCC, seven of which were preputial or penile in origin.17 The use of piroxicam was extrapolated from use in other species, such as rats, dogs, and humans, to treat SCC.16 Oral piroxicam was used to treat re- currence of non-genital SCC in a 16-year-old Morgan gelding.18 The SCC had initially been treated with intralesional cisplatin; 3 months after initiation of piroxicam therapy, the lesion and enlarged regional


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