January 2003 Research Round Up

First published in Veterinary Times March 2003

January’s journals contained three papers of interest to oncologists. Paoloni et al¹ studied the ultrasonographic and clinico-pathological findings in intestinal adenocarcinoma in dogs. They found that anorexia, vomiting, diarrhoea and weight loss were common clinical signs. Ultrasonographically, the tumours showed complete loss of wall layering (unlike the pseudolayering seen with gastric carcinoma). Other common ultrasonographic signs included poor echogenicity, an irregular lumen and fluid accumulation proximal to the lesion site. The median survival time was 233 days post surgical resection. A striking difference was noted in the survival of the sexes, with females appearing to have a much poorer prognosis than males.

            Simko et al² describe a retrospective study of canine apocrine sweat gland adenocarcinomas. These are relatively uncommon, accounting for 0.7% to 2.2% of skin tumours in dogs. 66% showed local invasion, but while one case of distant metastasis was observed, most of the cases that died of causes thought to be unrelated to the tumours were not subjected to post-mortem examination and so the authors were not able to predict the frequency with which metastasis occurs in this disease.

            Radiotherapy is a common treatment modality for nasal tumours. Correa et al³ evaluated the efficacy of cobalt-60 radiotherapy as a means of treating the uncommon tumour, nonkeratinizing squamous cell carcinoma of the nasal cavity. The median survival time was 165 days, and the authors conclude that this tumour is aggressive and compared to historical controls (radiotherapy of all nasal carcinomas) responds poorly to radiotherapy.

            Tibial plateau leveling osteotomy is an increasingly popular method of surgically treating cranial cruciate ligament rupture in dogs. However, there are few reports describing the procedure, its outcome and complications. Pacchiana et al⁴ review the treatment of 397 dogs by this technique. 28% of dogs suffered complications, and in 5% further surgery was necessary. Major complications (which accounted for 37% of complications) included infection, broken implants, patellar tendon desmitis and fractures of the tibia, fibula and patella. However, the authors noted that the incidence of major complications was similar to other methods of cranial cruciate ligament stabilisation.

            Two recent papers concerning infectious disease are of interest. Hackett and Lappin⁵ discuss the prevalence of enteric pathogens in a Colorado population. Faecal samples from dogs with acute diarrhoea of small or large intestinal origin were analysed, as were samples from age-matched, client-owned healthy dogs. Infectious agents potentially associated with gastrointestinal disease were isolated in 26% of the samples. 16.2% of samples were infected with potentially zoonotic agents, including some of the samples from healthy dogs. This has significance for dogs in the homes of immuno-compromised owners.

            Maggs et al⁶ discuss the use of L-Lysine in the treatment of feline herpes virus  infection in latently infected cats. The cats were infected with the virus, and 5 months later were rehoused and given 400mg of L-lysine daily. After 15 days, all the cats were given methyl prednisolone to induce viral re-activation. Cats receiving L-lysine had significantly fewer viral shedding episodes following rehousing than the control group, but not following corticosteroid administration. No adverse clinical effects were noted with this treatment.

            Two recent papers will interest endocrinologists. Gordon et al⁷ report a case of hyperthyroidism in a cat aged only 8 months. It responded to treatment involving unilateral thyroidectomy followed by radioactive iodine therapy, but developed clinical hypothyroidism. Good et al⁸ investigated the corneal sensitivity of dogs with diabetes mellitus. Using an aesthesiometer, they measured the corneal touch threshold. Diabetic dogs had significantly reduced corneal sensitivity, which was unrelated to duration of diabetes or status of glycaemic control. The significance of this finding is that, since the corneal nerves are important for regulating corneal protection by mediating tear production, corneal nerve dysfunction can lead to recurrent or non-healing ulcers in diabetic dogs.

            Diagnosis of poisoning by vitamin K antagonists such as warfarin can sometimes be difficult in the absence of the appropriate history of toxin consumption. Proteins induced by vitamin K antagonism (PIVKA) have been used as a test for anticoagulant rodenticide poisoning. Mount et al⁹ investigated the use of this test in 325 cases, by comparing the results with one-stage prothrombin time (OSPT) and activated partial thromboplastin time (APTT) in dogs with various clotting disorders. They found that, depending on the criteria used, a 98% specificity and 90% sensitivity for diagnosis of anticoagulant poisoning could be achieved. Severe liver disease can give false positive results and testing early in the course of the poisoning or after vitamin K administration can give false negatives.

            Phenoxybenzamine, a non-selective alpha-antagonist, has long been the drug of choice for relief of functional urethral obstruction in dogs and cats. However, in human medicine, this has been superseded by the use of selective alpha-1 antagonists such as prazosin. Fischer et al¹⁰  performed urethral pressure profiles in non-sedated male beagle dogs to assess to effects of phenoxybenzamine and prazosin. They found that maximal urethral pressure and maximal urethral closure pressure decreased significantly following prazosin injection, but this result was less consistent with phenoxybenzamine. However, there were significant drops in arterial blood pressure with prazosin but not with phenoxybenzamine.

            Also related to the urinary system, Albasan et al¹¹ have studied the effects of storage time and temperature on the pH, specific gravity and crystal formation in urine samples of dogs and cats. Samples were analysed either within 60 minutes of collection, or after storage at room or refrigeration temperatures for 6 to 24 hours. They found that storing for longer or at a lower temperature caused a significant increase in the number calcium oxalate crystals that formed. Specific gravity and pH were not significantly affected. The authors therefore recommend that urine samples are analysed within 60 minutes of collection.

            Finally, proof that dental chews are good for cats. Ingham et al¹² found that the daily addition of dental chews to a cat’s diet reduced plaque and calculus accumulation and reduced the severity of gingivitis.

1. Paoloni et al, Vet Rad & Ult 2003; 43, 562

2. Simko et al, Can Vet J 2003; 44,  38

3. Correa et al, JAAHA 2003; 39,  86

4. Pacchiana et al, JAVMA 2003; 222, 184

5. Hackett & Lappin, JAAHA 2003; 39, 52

6. Maggs et al, AJVR 2003; 64, 37

7. Gordon et al, JAAHA 2003; 39, 67

8. Good et al, AJVR 2003; 64, 7

9. Mount et al, JAVMA 2003; 222, 194

10. Fischer et al, Can JVR 2003; 67, 30

11. Albasan et al, JAVMA 2003; 222, 76

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