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.
The porokeratosis is probably the result of direct pressure on the plantar surface of the skin but is not usually associated with an underlying bony condition. There is still some debate as to whether the underlying ducts of sweat glands are involved.
• Plantar verrucae. These benign epidermal neoplasms are caused by a variety of different human papillomaviruses (HPV) viruses. Papillomaviruses are species-specific double-stranded DNA viruses and approximately 46 different ones have been implicated in the formation of human warts. Plantar warts may appear as punctate single lesions, large mosaic warts or multiple seed warts on the weightbearing areas of the foot. It is easy to mistake them for solitary hyperkeratotic lesions or heloma milliare.
In general, plantar warts have vascular elements within the lesion and show pinpoint capillary bleeding when you debride them. When you find warts on the direct pressure bearing surfaces of the balls of the feet, they may be painful and interfere with normal gait. Warts tend to show complete loss of the normal skin lines, whereas other keratotic lesions usually show radiating skin lines through the lesion.
Is Enucleation Enough For Keratotic Lesions?
There are basically two types of manual reduction of external hyperkeratotic tissues: debridement and enucleation. We use debridement for more superficial lesions, such as localized or generalized callus, hyperkeratoses and verrucae.
Enucleation is the technique you can use to remove the deep central core of lesions, such as nucleated corns, intractable plantar keratoses, porokeratosis plantaris discreta or seed corns (heloma milliare). In most cases, it is essential to debride the overlying callus prior to enucleation.
The goal of this process is to remove as much of the deep keratin plug within the center of the lesion in order to reduce pressure and discomfort. If you remove too much of the keratinous buildup, the skin may feel very tender, especially upon weightbearing. When you remove insufficient keratinous material, your patient may continue to have pain immediately after treatment.
In using enucleation, you may be able to reduce the pain level and make these lesions more tolerable for patients. However, in my opinion, most keratotic lesions do not resolve with this form of conservative therapy.
Pertinent Pearls On Injection Therapy
It may be worthwhile to treat certain keratotic lesions or conditions, such as the intractable plantar keratosis, porokeratosis, fibroma or keratodermas, with intradermal or intralesional injections.
The most common agents used for injection therapy, along with the local anesthetic, include corticosteroids and sclerosing agents. It may be necessary to employ a local infiltrative nerve block with a local anesthetic agent prior to giving an intralesional injection in the lower extremity. Since injections into the plantar aspect of the foot may be extremely painful, you may give a posterior tibial nerve block prior to any other injection on the sole area of the foot.
In many cases, you may mix the local anesthetic agent with the medication and then inject the combination of the agents into or directly below the painful lesion. Using skin coolants, such as ethyl chloride, will greatly decrease the patient’s perception of pain from the needle penetrating through the skin.
Additionally, you may actually inject some plantar foot lesions from a dorsal approach if you can use a long needle that passes between the metatarsals at the level of the lesion. In many cases, the patients report this is somewhat less painful than injecting directly into the plantar lesion from below.
Should You Consider Corticosteroid Injections?
Intralesional corticosteroid injections are not recommended for viral lesions such as warts but are commonly used for other lesions that are steroid responsive. Unfortunately, most keratotic lesions do not respond well to this form of injection therapy. Nonetheless, several preparations of corticosteroids suitable for intralesional injection are available.
In general, for superficial or small lesions, you may inject them with small amounts of the soluble steroids (sodium phosphate group). When you’re dealing with deeper, thicker or larger lesions, you may use the insoluble acetate or diacetate group of corticosteroids.
You’ll find that non-keratotic lesions, such as the bursa, mucoid cyst and ganglionic cyst, are frequently responsive to cortisone. Usually, you can do direct injections (intralesional) with small amounts of corticosteroids.
Depending upon the size of the lesion, you may place 1/8 to 1/4 mL of betamethasone or dexamethasone sodium phosphate centrally within the lesion. (Be aware that direct placement will enlarge the cyst and make it much more prominent.) You may mix this injection with equal volumes of a local anesthetic agent. You may perform repeat injections in two to six weeks, as needed, as long as the patient doesn’t experience any secondary complications of steroid injections.
When it comes to painful or inflamed intractable plantar keratosis, heloma durum, porokeratosis or other keratodermas, you may use cortisone injections intradermally or subcutaneously. These injections may consist of 0.2 to 0.5 mL of undiluted dexamethasone sodium phosphate. You can dilute these injections with equal amounts of local anesthetic agent. However, it is much more effective when you perform direct injections without mixing.
In most cases, the inflammation will improve but the lesion will not resolve. You may repeat this technique once or twice as needed and usually can combine it with some other conservative treatment (such as orthotic foot devices or shoe modifications) to accommodate the painful area.
Plantar fibromatosis, hypertrophic scars and keloid scars are other painful lesions that are responsive to cortisone. You can directly inject the cortisone into the central portion of the lesion with 1/8 to 1/2 mL of triamcinolone acetonide, 10 mg per mL suspension.
Be Aware Of Cortisone Injection Complications
Complications of cortisone injections are well documented and you may see them in susceptible patients. These complications may be the result of multiple injections or improper use of the products. The most common complications are subcutaneous atrophy, perilymphatic atrophy, hypopigmentation, hyperpigmentation, tendon atrophy and telangiectasia.
The atrophy of subcutaneous tissue is directly related to the strength of the steroid solution (mg per mL) used, the skin condition you’re treating, the quantity of steroid injected and the location of the lesion on the body. Local atrophy is usually temporary and is more likely to develop if you make the steroid injection at deeper levels, in or near the fat tissue or when you use higher concentrations of triamcinolone.
Do not inject intralesional steroids into areas that are already thin or atrophic or in areas of current or previous ulcerations. Also avoid using intralesional steroids in areas with cutaneous infections because they may exacerbate the infection.
When performing local steroid injections, be aware that perilymphatic atrophy may occur, especially when you’re treating dark-skinned patients. This phenomenon involves linear atrophy, usually with cutaneous hypopigmentation, that forms along the lymphatic vessels after you inject a steroid solution into an adjacent soft tissue lesion.
Sclerosing Agents: The Inside Scoop On Treatment Results
The most common type of sclerosing agent used to inject plantar foot lesions is a combination of dehydrated absolute ethyl alcohol and local anesthetic agent. You can prepare a 4% sclerosing alcohol solution by mixing 2 mL of dehydrated ethyl alcohol (absolute alcohol for injection) with 48 mL of 0.5% bupivacaine with epinephrine 1:200,000. This preparation is a 4% sclerosing solution of absolute alcohol by volume. The epinephrine presumably helps to keep the sclerosing agent in a small area and does not allow rapid absorption into the adjacent tissues.
Once you have mixed these solutions, it is extremely important that you cover the original label with a new one (which states this is now a sclerosing solution) in order to prevent accidental injection.
If your patient has plantar bursa with or without overlying callus formation and other cystic lesions, you may do an intralesional injection with 1/8 to 1/4 mL of 4% alcohol sclerosing solution. You may repeat this up to three times at weekly intervals. The sac or cyst tends to shrink in the following weeks, with a dramatic decrease in symptoms and callus formation which may last as long as one year.
For plantar fibromas, you would inject 0.5 mL to 1.0 mL of 4% alcohol sclerosing solution directly into the central portion of the mass. Subsequent injections may be infiltrated throughout the mass. You would follow the injection with a five- to 10-minute ultrasound treatment. Repeat this weekly for up to seven visits. Expect to see additional softening and shrinking of the fibroma for several months after the final injections.
Porokeratosis plantaris discreta and other punctate or deeply nucleated plantar lesions respond extremely well to 4% alcohol sclerosing injections. Using a 1mL tuberculin syringe and a 5/8-inch, 25-gauge needle, you can inject a total of 0.25 mL to 1.0 mL (depending upon the size of the lesion) of 4% sclerosing solution at a 45-degree angle to the lesion. Repeat this injection procedure at weekly intervals for up to seven injections. Larger punctate lesions will also respond to a similar injection process of weekly intervals.
Usually, you’ll see dramatic change by the third injection. If the lesion has responded, no further treatment is necessary. However, if you have performed three injections and have gotten poor or no response, terminate the program and recommend alternative treatments.
The weekly intervals seem to be relatively important and longer intervals between injections may delay the end results. Again, once the local anesthesia wears off, there may be considerable burning or pain at the injection site that may last for several hours. You can reduce this discomfort by applying cool foot soaks or ice to the area. Analgesics, especially aspirin, may also help reduce the pain.
The remarkable thing about this treatment is not only do the lesions become asymptomatic in nature, presumably due to the chemical neurolysis that occurs following the alcohol injections, but the lesions frequently go away. Over the past 25 years, I have seen very few recurrences of lesions once they have responded to the injection process.
What About Complications With The Sclerosing Alcohol Injection?
There are very few reported cases of complications with 4% alcohol injections. Some of the risks include an increase in nerve pain shortly after the first or second injections, which is presumably due to nerve irritation secondary to neurolysis. This resolves quickly in almost all patients and does not appear to be a long-term risk.
You may also notice an erythematous response following the alcohol injection in which the skin around the injection site appears red and small streaks may appear in a pattern somewhat similar to what you would see in cellulitis. This is probably a perilymphatic reaction to the alcohol and is self-limiting. Finally, there is a chance the alcohol treatment program will not work for one reason or another. In this case, you may perform alternative treatments like surgery.
There are numerous painful keratotic and punctate skin lesions on the feet, many of which you can treat with changes in shoe styles, local tissue debridement, padding and strapping and accommodative shoe inserts. In some of these cases, though, the painful lesions may continue to be a problem and the addition of injection therapy may greatly improve or resolve these conditions.
Dr. Dockery is a Fellow of the American Society of Podiatric Dermatology. He is the Founder and Director of Scientific Affairs of the Northwest Podiatric Foundation for Education & Research, USA in Seattle, and has a private practice at Mill Creek Foot & Ankle Clinic in Seattle.
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