Eosinophilic Collagenolytic Granuloma is most familiar as an ulcerative-to-nodular lesion of the feline lip or palate, but a histologically identical lesion affects the footpads. The history that I receive is of non-healing ulcerative and proliferative lesions affecting one or more pads, often on several feet. Over 1/3 of cases occur in cats less than one year of age, and virtually all affected cats are less than 5 years of age. About 1/3 of the cases have concurrent lip, tongue, or palatine ulceration typical of eosinophilic granuloma.

Digital Soft Tissue Sarcoma (Fibrosarcoma, Giant Cell Tumor of Soft Tissue) is the most common digital neoplasm in cats. It affects older cats (mean of 10.1 years) and presents as a proliferative osteolytic lesion affecting a single digit. I have received no follow-up information about metastatic potential, but these look like high-grade anaplastic sarcomas. If their behavior follows the pattern of other such sarcomas, they should be locally destructive, have a high risk of local recurrence, but negligible metastatic potential.

Bronchial Adenocarcinoma Metastatic to Digit seems like an improbable and rare diagnosis, but in fact this is a relatively frequent syndrome reported worldwide. The usual clinical presentation is of multiple painful / swollen footpads on multiple feet in an old cat (mean age of 14 years) that otherwise seems healthy. There is virtually never clinical evidence of the primary bronchial tumor at the time the cat first presents for lameness. Although this tumor eventually undergoes widespread metastasis to many organs, the footpads are apparently a preferred target. As seen in core or larger excisional biopsies, the footpad contains numerous invasive acinar / tubular structures that have ciliated columnar epithelium. The proliferating tumor stimulates abundant fibrosis, and creates a footpad that is swollen and hard. The prognosis is terrible because widespread random metastasis is inevitable.

Squamous Cell Carcinoma is a very frequent osteolytic tumor of the canine digit, but the veterinary literature contains no reported cases in cats. Within the last four years, I have diagnosed 9 such tumors. Unlike the relatively benign behavior of these tumors in dogs, the feline tumors appear to be quite aggressive. Of the 8 cases for which I have reasonable follow-up, 5 developed metastatic disease within the year following the initial amputation. Three of these 5 were euthanized within a few weeks of the initial diagnosis because of confirmed nodal metastasis. Only one of the 8 cases has apparently been cured by the digital amputation. The postoperative interval in the two remaining cats is not yet long enough to provide me with any reliable information.

Pemphigus Foliaceus occurs as a crusting, pustular skin disease that most commonly affects the face and, particularly, the ear pinnae. In my experience, it is the most common neutrophilic skin disease of cats (bacterial pyoderma is inexplicably rare in cats). In the four year period that I surveyed, there were 75 cats diagnosed with pemphigus foliaceus, and 6 of these were submitted because of crusting and ulcerative lesions specifically affecting the nailbed of several digits. The histologic diagnosis usually is quite straightforward, with large flat neutrophilic crusts and pustules containing the individualized acantholytic epithelial cells that are floating within this sea of nonlytic neutrophils. Virtually all of the cases that I have seen are from cats that have undergone chronic, unsuccessful treatment for suspected bacterial or fungal disease.

Plasma Cell Pododermatitis is an enigmatic and uncommon disease with a distinctive and repeatable clinical presentation: multiple pads on multiple feet (almost always including the main metacarpal / metatarsal pads) become soft, "putty-like", and develop a violet discoloration. They seem painful, but most of the cases do not present with outright ulceration. The histologic diagnosis is easy because these cases exhibit remarkably little variation from the classical theme of massive diffuse plasmacytic infiltration below the intact epithelium. The pathogenesis of this lesion (like so many feline skin diseases) remains completely unknown.