Site of ulcer
Consideration of ulcer site is very important in assessing severity of infection. The skin barrier around the forefoot is relatively thin compared to the hind foot and the forefoot can be further compromised if digital deformity or dysfunction is present, due to increased pressure over digital bony prominences.
If forefoot sites ulcerate, exposure to deeper underlying fascia and bone is more common, increasing the risk of osteomyelitis if infection is untreated. Usually, the need for repeated courses of antibiotics provides a clue that we are dealing with a deeper-seated infection, which will require antibiotics that are appropriate for the treatment of osteomeylitis. Ulcer assessment may require radiological imaging if osteomyelitis is suspected.
Another issue regarding the site of ulceration is the potential contribution from fungal infections. Both tinea pedis and onychomycosis may be present on the foot. Although these problems may be asymptomatic, they should be treated in higher risk patients with diabetes.
Tinea pedis can lead to soft skin irritation, inflammation and fissuring which becomes a portal for secondary bacterial infection. Skin scrapings for microscopy and microbiological culture can be used to confirm tinea pedis and topical treatment, for example terbinafine cream, should be considered.
Untreated fungal nail infection can cause problems because onycholysis and subungual hyperkeratosis increases pressure on the nail bed and compromises the integrity of the nail unit, particularly with concomitant peripheral arterial disease (see below)
Onychomycosis with nail dystrophy
