There are a number of keratotic and painful lesions that form on the weightbearing and pressure areas of the foot. You’ll often find that many of these conditions won’t respond to simple debridement and padding, and ultimately prove to be difficult to treat. In general, hyperkeratosis indicates an increased keratinocyte activity resulting from stimulation of the epidermis by intermittent or increased pressure.
Abnormalities in keratinization may represent thickenings, which are commonly referred to as corns, calluses, helomas, hyperkeratoses or tylomas. However, be aware that several unrelated keratotic-like lesions have appearances similar to corns and calluses. These conditions include arsenical keratosis, eccrine poroma, keratodermas, plantar verrucae and porokeratosis plantaris discreta.
With calluses or tylomas, you’re looking at hyperkeratoses that are diffuse and generalized. You’ll generally find these on the weightbearing surface of the sole of the foot and they’re usually asymptomatic. You would see this diffuse hyperkeratotic tissue more often in patients who regularly go barefoot and those who have a form of posterior equinus.
If the hyperkeratoses are more distinct and isolated, you’re likely looking at corns or helomas, especially on the toes. The more discrete types of hyperkeratosis are frequently painful and you’ll often find these on the ball of the foot. When you evaluate these lesions closely, you may detect a central conical core of keratin at the point of greatest pressure.
Discrete isolated lesions may also be similar to cutaneous horns but unlike skin horns, careful debridement of hyperkeratotic lesions will lift the superficial keratin plug off completely, leaving visible skin lines underneath.
You may see other distinct areas of pressure hyperkeratosis formation under individual metatarsal heads. Keep in mind that these lesions are frequently resistant to regular conservative care of debridement and protective padding. These lesions are referred to as intractable plantar keratoses (IPKs).
An Overview Of Lesion Types
As I noted above, there are other lesions that may be visibly similar to corns and calluses. In order to differentiate between these different lesions and obtain the best treatment results for your patients, be aware of the following conditions.
• Arsenical keratoses. These discrete hyperkeratotic lesions, which you may see on the soles of the feet and palms of the hands, are secondary to arsenic exposure. Keep in mind these lesions may mimic discrete intractable plantar keratoses, seed corns (heloma milliare) or plantar verrucae. This condition is typically found on the weightbearing foot and is usually very difficult to treat.
• Eccrine poromas. Slow-growing, painless, superficial, smooth-surfaced and partially flattened, these lesions may resemble pyogenic granulomas, dermatofibromas or foreign-body granulomas. Eccrine poromas may appear rubbery to firm and can reach 3 cm in diameter. You’ll usually see eccrine poromas in female patients in their 40s. Typically, these lesions are on the heel or ball of the foot.
• Keratodermas. Localized forms of keratodermas may be similar to diffuse, generalized or isolated forms of hyperkeratosis. Most types of keratodermas are inherited as autosomal dominant traits and may also be associated with systemic manifestations.
Diffuse hyperkeratosis of the plantar skin may become so thick it tends to form cracks or fissures, and may become very painful for the patient to walk on. The punctate form of palmoplantar keratoderma looks very similar to arsenical keratoses with the exception being a central translucent center that is common in each lesion.
• Porokeratosis plantaris discreta. These distinct punctuate lesions are small (1 to 3 mm in diameter), have a white or yellow-white color and are particularly tender with side-to-side pressure. With these lesions, you’ll usually see them on the weightbearing aspect of the ball of the foot, but they may be found on non-weightbearing areas.