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Differential diagnoses for draining tract lesions in dogs and cats (Proceedings)

May 01, 2011

Draining tracts or fistulous tracts are tract lesions that connect with a central area or focus of inflammation to the skin's surface. Draining tracts are most commonly associated with nodules which are large (greater than 0.5 cm), firm, raised usually circular lesions that extend down into the dermis. These nodular lesions occur because of neoplasia or inflammation. This makes the differential diagnoses list extensive. As a result, draining tract lesions can be frustrating and a diagnostic challenge for many veterinarians. Therefore, it is important to be familiar with the differential diagnoses, diagnostic tests available and necessary to treat draining tracts and treatment options for these cases. The prognosis will vary depending on the reason that the dog is developing these lesions. An accurate diagnosis is therefore imperative for the pet's health.

Clinical signs

No specific age, sex or breed predispositions exist for dog developing draining tract lesions. Draining tract lesions can be solitary lesion or can be associated with multiple lesions. These lesions can be anywhere on the body but the most common lesion locations are on the feet and trunk. As stated previously, the draining tract lesions are most commonly associated with nodules. The draining tract lesion occurs when the nodule ruptures. The draining tract has scant to copious amounts of exudates coming out of this skin lesion. This exudates can be serous, serosanguinous, or purulent. Granules may also be present. Dogs and cats may lick the draining tract area the area from discomfort. This excessive licking results in partial to complete alopecia being present around the draining tract lesion. If the draining tract lesion is located on the foot or feet then lameness may occur. The presence of depression or inappetence may be present when systemic disease is present.

Differential diagnoses

As previously stated, draining tract lesions can be due to a wide variety of underlying etiologies. The four most common causes are infectious, parasites, neoplasia and noninfectious/non-neoplastic causes. Bacteria and fungus are cause infection in the skin and draining tract lesions. These lesions can be due to any bacteria but some of the more common bacteria that cause draining tract lesions are Actinomycosis, Nocardiosis, Mycobacteriosis, Botrymomycosis, Actinobacillosis and L-form infections. Examples of some of the more common fungal infections that can cause draining tract lesions include: Blastomycosis, Histoplasmosis, Crytpococcosis, Coccidiomycosis, Aspergillosis (usually nasal area), Pythiosis, Sporotrichosis, Phaehyphomyocosis, Kerion (dermatophytosis). Parasites of the skin that can cause draining tract lesions are demodicosis, cutaneous, Dirofilariasis and Leishmaniasis. Some of the more common neoplasms that can cause draining tract lesions are mast cell tumor, melanomas, SCC, cutaneous histiocytosis, systemic histiocytosis, malignant histocytosis, and cutaneous lymphoma. Examples of non-infectious/non-neoplastic causes for draining tract lesions include: foreign bodies, eosinophilic granulomas, sterile nodular panniculitis, sterile granulomas, nodular sebaceous adenitis, calcinosis cutis, and juvenile cellulitis.