dvm360.com: Interdigital Furunculosis - Medical and Surgical Options

Interdigital furunculosis (IF) and folliculitis, sometimes called interdigital cysts, can occur for multiple reasons. Lesions include interdigital erythema, edema, nodules, hemorrhagic bullae, hemorrhagic draining tracts, ulcers, and scarring. The most common reason for IF is allergy. The skin of the paws, especially the interdigital skin, becomes inflamed with an allergy flare, leading to barrier dysfunction and pedal pruritus. Pruritus is manifested as licking, which can cause trauma to the hair follicles, causing folliculitis. Pieces of hair shaft (keratin) will become pushed into deeper tissues, causing a foreign body reaction. Due to continued inflammation and licking, secondary infection becomes a problem, which causes more inflammation. A cycle of inflammation/infection ensues, which can lead to antibiotic resistance, scar tissue, and cellulitis. In allergic dogs, multiple paws and interdigital spaces will be affected and there often will be other signs of allergic skin disease (eg, more general pruritus, and recurrent skin infections). Affected animals are often short-coated, allergy-prone dogs like pit bull terriers, Great Danes, English and French bulldogs, Labrador retrievers, Chinese shar-pei, and bull terriers.

In nonallergic dogs, the mechanism of IF is mechanical. Furunculosis will often develop only between digits 4 and 5 on the front paws. Affected animals are often larger-breed, heavy dogs like mastiffs, English bulldogs, and Labrador retrievers. Dogs with webbed paws, deep palmar interdigital pockets, obesity, and conformation abnormalities are more prone to this type of IF. The increased weight of these heavier dogs will cause friction between this interdigital space, resulting in follicular plugging and comedo formation on the palmar surface of the paw. Dogs with conformation changes secondary to arthritis and resulting in valgus deviation of digit 5 are also prone to interdigital friction and comedo formation. Smaller dogs prone to arthritis-related IF are Shetland sheepdogs and Cavalier King Charles spaniels.