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Compendium September 2012 (Vol 34, No 9)

Clinical Snapshot: A Corn in a Whippet

by Anne Fawcett, BA (Hons), BSc(Vet) (Hons), BVSc (Hons), CMAVA, Angela Phillips, BVSc, MVS, MACVSc

    Case Presentation

    A 6-year-old, neutered whippet presented for chronic, intermittent lameness of the left thoracic limb. The lameness was pronounced when the dog walked on hard surfaces such as concrete and was markedly reduced when the dog walked on soft ground (e.g., grass, sand). The dog had previously been treated with an NSAID (carprofen, 2 mg/kg PO q24h) for 14 days with no improvement.

    On physical examination, there was a focal, circular region of hyperkeratosis on the digital pad of the third digit of the left thoracic limb (FIGURE A). All other digital pads on all paws were normal. Digital pressure on the lesion elicited pain. No pain was elicited elsewhere upon palpation or manipulation of the bones or joints in the affected limb. There was marked dorsal elevation of the nail of the affected digit.

    Figure A.

    1.    What is the most likely diagnosis?

    2.    What is the likely etiology?

    3.    What is the recommended treatment?

    Answers and Explanations

    1.    A corn or paw pad keratoma. In dogs, corns are circumscribed hyperkeratotic regions of the digital pad with central, conical keratin cores that are sensitive to pressure.1 Most are located at the center of the digital pads that bear the most weight, but they are occasionally found on metacarpal and metatarsal pads.1 The differential diagnosis for pad lesions includes papillomas,2 epidermal cysts,1 and paw pad foreign bodies1; however, the location and appearance of these lesions are typically clinically distinguishable from those of corns. Definitive diagnosis is via histopathology. Lameness is typically worse when affected dogs walk on hard surfaces because the hard core of the corn is forced into surrounding tissue.1

    2.    Current evidence suggests that a mechanical etiology is most likely. In one study,1 anatomic deformities of the foot were detected in 40% of cases, with damage to the deep digital flexor tendon in half of these. Where complete rupture had occurred, there was marked dorsal elevation of the nail,1 as in this case. The study author speculated that damage to the deep digital flexor tendon leads to elevation of the nail and subsequent caudal weight bearing on the digital pad. Previous surgery, trauma, and foreign body penetration were also associated with corns in this study.1 In the presented case, histopathologic evaluation of the lesion revealed no evidence of inflammation or foreign material (e.g., plant material, grit) that might indicate a penetrating wound. Plain radiographs of the digits revealed no evidence of radiopaque foreign bodies.

    3.    Surgical excision of corns that are associated with pain (evidenced by lameness and/or pain with digital pressure on the lesion) is recommended, despite a recurrence rate exceeding 50%.1 Recurrence is twice as likely for dogs with concurrent foot deformities than those without.1 Repeat excisions may be an acceptable means of management in select cases.1 In refractory cases, distal digital ostectomy may be requiredto definitively resolve lameness.1 Other treatments, including laser surgery to excise the corn, curettage, and subdermal implanation of silicone block gel particles, have yielded unsatisfactory results1; however, anecdotal evidence suggests that curettage can provide relief for many months and should be considered as an alternative to surgery.

    ***

    In this case, a diagnosis of a digital corn was made on the basis of the clinical appearance and anatomic location of the lesion and histopathology results. Corns are known to cause severe, chronic lameness in racing greyhounds and other, related breeds.1 Surgical excision was performed to spare the digit and because it is potentially curative. The corn was removed, with fine margins, using a 6-mm biopsy punch while the dog was under general anesthesia (FIGURE B). The pad was sutured using simple interrupted sutures (3/0 Biosyn [Monofilament Glycomer 631, Synature]; FIGURE C). The foot was placed in a well-padded dressing that was changed at weekly intervals for 3 weeks until the sutures were removed.

    Figure B.

    Figure C.

    The owners were advised of the risk of recurrence and instructed to walk the dog on soft surfaces and to cover the paw in a soft, protective bootie to limit trauma to the digit. One month after surgery, the dog’s lameness was markedly decreased. The owners declined a digital ostectomy and elected to tolerate mild lameness.

    References

    1.    Guilliard MJ, Segboer I, Shearer DH. Corns in dogs; signalment, possible aetiology and response to surgical treatment. J Small Animal Pract 2010;51:162-168.

    2.    Balara JM, McCarthy RJ, Kuipel M, et al. Clinical, histologic, and immunohistochemical characterization of wart-like lesions on the paw pads of dogs: 24 cases (2000-2007). J Am Vet Med Assoc 2009;12:1555-1558.

    References »

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