The parasitic mite Demodex can infect the haired skin of the feet and result in pododermatitis. Demodex mites are present in very low numbers in the skin of all dogs, but in some patients, either due to a genetic susceptibility, or due to a process that lowers the immune system, these mites can populate the skin in very large numbers causing disease (Fig 1.).
Figure 1: A case of pododermatitis due to Demodex mites (feet have been clipped for cleaning).
Foreign bodies like grass seeds are a very common cause of pododermatitis in dogs. Foreign bodies tend to penetrate the skin of the feet when dogs are out walking/running and then trigger inflammation when they become trapped within the feet.
Allergic diseases in dogs and cats are very common, and result in inflammation in the skin. This inflammation is very commonly seen affecting the feet, and results in redness, excessive licking and chewing at the affected sites.
Certain hormonal diseases can also be involved in the development of pododermatitis as the local skin immune system is reduced and the ability to fend off infections is compromised.
A very common feature of pododermatitis, particularly in dogs, is a deep infection of the feet. This is usually due to bacteria, but can be due to rare fungal organisms, and often results in multiple painful, swollen and discharging lumps (Figure 2).
Figure 2: Bleeding lumps between the toes due to deep bacterial infection
A frustrating cause of pododermatitis is termed conformational pododermatitis. This usually occurs in heavy set dogs with excessively splayed feet. This results in weight bearing on hairy parts of the feet adjacent to the footpads and triggers inflammation of the hair follicles. Over time, this inflammation damages the hair follicles and results in chronic inflammation within the feet.