Sarcoids are the most common skin tumours of the horse. They occur as several different forms: verrucous, occult, fibroblastic, nodular, mixed and malevolent. The fibroblastic form presents particular problems in diagnosis in that it has a fleshy, ulcerated appearance which may be indistinguishable from exuberant granulation tissue (proud flesh). Sarcoids are even more difficult to identify when they occur at the site of an open wound and are mixed with granulation tissue. A biopsy (removing a small piece of tissue for examination under the microscope) which is used for the diagnosis of other skin conditions is often best avoided if a diagnosis of sarcoid is suspected because of the risk of making the condition worse. Furthermore, small biopsies may not include enough tissue features to reach a diagnosis.
Differentiating between ulcerated sarcoids and exuberant granulation tissue may soon be easier thanks to a technique developed in Belgium.
There is increasing evidence that the bovine papilloma virus (BPV) is responsible for sarcoids in horses. Dr Ann Martens and co-workers at the University of Ghent in Belgium, have reported recently on a technique for detecting BPV-DNA using swabs or superficial scrapings from suspected sarcoids.
Sarcoids from the different clinical types were included in the study on the basis of clinical diagnosis. A biopsy was not taken unless the sarcoid was removed (because of the risk of exacerbating the condition.) However, if a sarcoid was treated surgically, the diagnosis was confirmed microscopically.
A superficial swab and scraping were taken from each sarcoid. If there was no ulceration the swab was moistened with phosphate buffered saline, to encourage cells to adhere to the swab. Scrapings were collected from various parts of the sarcoid surface. Care was taken to avoid scraping hard enough to cause bleeding. After collection the samples were stored in a deep freeze until examined. Swabs and scrapings were also taken from normal skin, melanomas, open wounds and other skin abnormalities for comparison.
The samples were examined for the presence of BPV-DNA using a polymerase chain reaction technique, a very sensitive method of detecting genetic material. Overall, BPV-DNA was found in 88% of the successful swabs and 91% of the successful scrapings from sarcoids. It was detected in 100% of samples from sarcoids with superficial ulceration, but in only 50% of occult sarcoids. It was not isolated from any of the non-sarcoid lesions.
The technique failed to detect DNA in 12% of swabs and 7% of scrapings. Dr Martens suggests that further studies are required to see if other techniques of DNA isolation would give better results.
She points out the advantages of this technique. The sampling procedure is easy. There is only a minor risk of exacerbating the condition when scraping the surface or rubbing with a swab. She advises that " special attention must be paid to obtaining sufficient superficial cellular material without damaging the intact epidermal surface."
This technique offers no advantages over clinical appearance for diagnosis of most types of sarcoids. But it proved very useful in ulcerated lesions for the differentiation of sarcoid from granulation tissue. It opens the possibility of detecting sarcoid involvement in wounds or sarcoid recurrence after removal.
For more details see: A Martens, A de Moor, R Ducatelle. PCR detection of Bovine Papilloma Virus DNA in superficial swabs and scrapings from equine sarcoids.The Veterinary Journal (2001) 161, 280-286.