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Case Report: Digital Cutaneous Viral Papilloma in a Scottish Terrier

A six-year-old, male, neutered Scottish terrier  presented with a two week history of acute onset, progressive, left thoracic limb lameness.  There had been no response to either rest or NSAIDs. The dog subsequently started licking the medial aspect of the left manus but on examination, no lesions were found.  Additionally, there had been resentment to neck manipulation just prior to referral.

Examination 

On presentation, the dog was bright and comfortable. He was ambulatory with a 5/10 lameness of the left thoracic limb.  General physical examination revealed an enlarged, left, prescapular lymph node.  Cervical spinal pain was evident on both left and right lateral flexion of the neck. Neurological examination was normal.  Orthopaedic examination revealed discomfort on palpation of both digits 3 and 4 of the left manus, but no gross lesions were detected.

Further Investigations

Routine blood-testing showed mild increases in haematocrit, ALT and TBIL, but was otherwise unremarkable.

fig.1 - dorsal STIR slice of manus at level of proximal margin of digital pads; there is increased signal strength within the soft tissues between digits 3 & 4.

On the basis of the above, it was thought possible that the pedal discomfort might be due to nerve root signature secondary to a C6-T2 lesion; MR-scans of the cervico-thoracic spine, left brachial plexus and brain were performed, which were all found to be unremarkable.   Given the clinical finding of resentment to palpation of the digits, the left manus was subsequently scanned.  An area of increased signal intensity on T2W and STIR sequences (fig. 1) was found , extending from the pads of digits 3and 4, along the interdigital soft tissues and tracking proximally along the abaxial side of the third digit. The foot was clipped to facilitate closer examination of the skin but again, no sign of inflammation, penetrating wounds or other lesions was apparent. A cisternal CSF tap was performed and the prescapular lymph node was aspirated for cytology and bacteriology.  The dog was placed on broad spectrum antimicrobials (amoxiclav) pending results.

The dog made an uneventful recovery from anaesthesia and was hospitalised for repeat assessment the following day.  At this time, the 5/10 left thoracic limb lameness was still present, but the neck pain had resolved. The foot was still painful on examination especially in the distal interdigital area between digits 3 and 4. The dog was discharged with a continuing course of antimicrobials and NSAID analgesia, pending results of the CSF and lymph node aspirate.

Results

fig.2 - Haematoxylin & eosin x400 - shows keratinocytes (hexagonal cells on right) expanded by a grey/blue fibrillary cytoplasm . There is peripheralisation of the nuclear chromatin caused by intranuclear inclusion material (pale pink) evidencing a viral cause.

CSF analysis was found to be unremarkable.  Lymph node cytology was consistent with reactive change possibly due to inflammation in the distal limb.

The dog was re-examined approximately one week later: the referring vet had noticed a small circular lesion which had appeared on the palmar aspect of the distal interdigital skin between digits 3 and 4. Although this area was not part of the pad per se, it was contiguous with both pads of P3 and P4 and was of the same consistency.  The area had been probed to investigate the possibility of the presence of a sinus tract but there was no evidence of extension into the soft tissues of the foot. The lesion comprised a circular, hard area of hyperkeratosis which appeared macroscopically to resemble a corn.  The surrounding area was thickened and painful when palpated.

The interdigital lesion was excised en bloc and submitted for histopathology. Closure was routine and a light dressing was applied to enclose the manus.

Subsequent to surgery, the lameness initially improved but recurred a few days later. This was ascribed to minor wound dehiscence, which was managed conservatively and the dog has since made a full recovery, with no further recurrence of the lesion or lameness.

Histopathology revealed a papilloma with mild secondary furunculosis.  Excision appeared to be complete and a viral aetiology was confirmed by the multifocal presence  of large amphophilic intranuclear inclusion bodies (fig. 2).

Discussion

Viral papillomas are usually multiple and frequently affect the oral cavities of young dogs.  They have also been described in adult, immuno-suppressed individuals (e.g. those undergoing chemotherapy).1,2  Lesions commonly appear 4-8 weeks after viral inoculation, initially, as small pale smooth elevated areas that subsequently develop into the classic cauliflower-like lesion.  These spontaneously regress after a further 4-8 weeks in most cases. Papillomatosis is normally considered a benign disease although there have been reports of transformation to malignant squamous cell carcinoma.  In addition, there is some evidence to demonstrate the presence of the virus in de novo squamous cell carcinomas, although in this situation, there remains the possibility that a primary lesion may have been missed clinically.3

Cutaneous papillomatosis is less common and although also viral in origin, it affects a broader age range and regression is often prolonged.  Lesions may occur anywhere on the body, but the digits do not appear to be a predilection site; they have however been described as causing lameness in an adult Siberian husky, successfully treated by digital amputation4.

A rare form of cutaneous papillomatosis has also been described in greyhounds, in which the lesion occurs in the interdigital area of the pads as in this case.In contrast, keratomas arising within the digital pads of greyhounds are termed ‘corns’.   They are most commonly found within pads 3 and 4 of the manus.   A proposed aetiology is the excessive forces generated within the tissues during racing, but there is also some evidence to suggest that foreign body penetration may cause these lesions to form.  Electron microscopy of corns has however, failed to find any evidence of a viral aetiology.6

Treatment of viral papillomas is often unnecessary due to spontaneous regression; but in cases where clinical signs have persisted, sharp excision, cryo- or laser surgery have all proved successful.  Interferon has also been tried with some success, as have live vaccines although these have the potential to cause squamous cell carcinomas at their injection sites.  Azithromycin is an azalide subclass macrolide antibiotic used for the treatment of papillomatosis in humans.  It has been trialed in dogs with reported success.  The mechanism of action in treating this disease is however, still unclear.2

Although surgical excision in this case was successful, had the papilloma recurred,  the use of azithromycin might be considered as an alternative to repeat surgery.

At the time of writing, there has been no evidence of recurrence.  Should lesions re-form, further investigation of possible underlying immunosuppression would be warranted.

References

1  Macy DW (2007): Tumor- causing viruses of dogs in Small Animal Clinical Oncology Withrow SJ and Vail DM, editors: , Missouri, , WB Saunders.

2 Yagci BB, Ural K, Ocal N and Haydar Edeoglu AE (2008): Azithromycin therapy of papillomatosis in dogs: a prospective, randomized, double-blinded, placebo-controlled clinical trial. Veterinary Dermatology  19(4) 194-8

3  Zuagg N, Nespeca G, Hauser B, Ackermann M and Favrot C (2005): Detection of novel papillomaviruses in canine mucosal, cutaneous and in situ squamous cell carcinomas. Vet Dermatology 16(5): 290-8

4  Plattner BL and Hostetter JM (2009): Cutaneous viral papilloma with local extension and subungual cyst formation in a dog. J Vet Diagn  Invest  21(4) 551-4

5  Davis PE, Huxtable CRR, Sabcine M (1976): Dermal papillomas in the racing greyhound. Australasian Journal of Dermatology 17 13-16.

6 Guillard MJ, Segboer I and Shearer DH (2010): Corns in dogs; Signalment, possible aetiology and response to surgical treatment. JSAP 51(3):162-168