Psoriasis on the foot: how to recognise and treat it

Psoriasis is a growth disorder of the keratinocytes, which are the cells that make up the epidermis. The haphazard growth of the cells results in the formation of reddened and flaky skin in some areas.

Clinical overview

There are three characteristics of psoriasis

• erythema
• overgrowth (plaques)
• desquamation

Psoriasis on the feet

Psoriasis on the feet does not usually cause plaques to form as in the rest of the body. This is because the skin is constricted within shoes which makes the skin more moist and makes any scaling that does happen less obvious.
Psoriasis on the foot manifests itself in a polymorphous manner and looks quite different from the rest of the body, which can make it more difficult to diagnose. Despite all this, the usual psoriasis symptoms of erythema, plaque and scaling are still present.
There are five categories of foot psoriasis:

• Plantar psoriasis
• Pompholyx (dyshidrotic eczema)
• Nail psoriasis (psoriatic onychopathy)
• Dorsal psoriasis of the foot
• Psoriatic arthritis of the foot

Plantar psoriasis

Plantar psoriasis is very common and, in cases of palmoplantar psoriasis, will be combined with the palmar form of the condition.
The appearance of plantar psoriasis varies considerably depending on whether it is inflammatory, hyperkeratotic or desquamated.
Its appearance can also vary due to factors such as the person being overweight, the type of footwear used and past psoriasis treatment, particularly that of cortisone. However, in most cases, plantar psoriasis is well demarcated, erythematous and causes scaly patches to form.
The photo shows a predominantly erythematous form of plantar psoriasis. Hyperkeratosis is present only at the heel and is caused by pressure or friction against the skin. While desquamation is minimal due to the particularly moist condition of the plantar skin, there is clear demarcation between the plantar area with psoriasis and the healthy dorsal skin.

Hyperkeratotic psoriasis

Hyperkeratotic plantar psoriasis causes the formation of hyperkeratosis plaques on the sole. In areas where particular pressure is applied such as on the heel, this form of psoriasis can also cause fissuring and desquamation, but will appear more mildly in non-weight bearing points.

Plaque psoriasis

Plaque psoriasis is less common. It can be recognised by patchy plaques on the skin which are caused by the uneven scaling of the stratum corneum due to abnormal keratinocyte growth underneath this layer of skin.
In some cases, and in the photo below, all three clinical indicators (erythema, hyperkeratosis, and scaling) are equally present on the same foot. As the photo below shows, hyperkeratosis doesn’t necessarily affect the whole sole of the foot. In this case, it spares the arch but diffuses across the rest of the plantar area. In other cases, the opposite occurs. As the photo below shows, psoriasis affects only the arch of the foot, leaving the rest relatively untouched. Localized, clearly-defined hyperkeratosis that has not been caused by friction or pressure should also be diagnosed and treated as a case of psoriasis.

Palmar plantar pustulosis (PPP)

Palmar plantar pustulosis (PPP) is one of the most common presenting forms of plantar psoriasis and often causes small vesicles to form below the stratum corneum.
The vesicles are collections of serum and mainly neutrophilic leukocyte cells within the epidermis.
Over time, the vesicles surface and open onto the stratum corneum, causing redness scaling and a small, crater-like indentation to form where the vesicle has opened.
PPP often causes severe itching and burning, at least until the vesicles open.
In some cases and in the photos below, PPP can appear with large bullous lesions, caused by the confluence of multiple vesicles.
PPP may also cause cloudy, creamy pustules with pus-like contents. These pustules are sterile and should not be confused for other plantar inflections, such as abscesses.

Dorsal psoriasis

Psoriasis may exclusively affect the dorsal region of the foot. Instead of hyperkeratosis and desquamation, the most obvious sign of psoriasis on the dorsal is that of erythema which is in part due to the role footwear plays.
The fact that psoriasis can affect either the dorsal or plantar portion of the foot demonstrates the fact that the foot is composed of two very distinct regions.
While skin of the feet may appear to be the same, in the face of the same pathological conditions, the two regions have very different, independent reactions from the other.

Nail psoriasis (psoriatic onychopathy)

One of the most common forms of psoriasis in the feet is that which affects the nails. Also known as psoriatic onychopathy, nail psoriasis causes the laminae, often of the first toe, to change color and shape. The nails may become opaque, yellowish or light brown, while the lamina may detach from the nail bed. In addition, scales that are particularly difficult to remove may form in between the detached lamina and the nailbed. In acute forms of nail psoriasis, the nail completely detaches and falls off. For reasons that remain unclear, many people with nail psoriasis receive a misdiagnosis of nail mycosis. This means that they receive treatments for mycosis which include lacquers, antifungal creams and sometimes oral medication which, of course, do not lead to any improvement in cases of nail psoriasis and can actually worsen the condition.

Treatment

As with other forms of psoriasis, foot psoriasis should not be treated with cortisone. While cortisone will initially reduce symptoms of psoriasis and may lead to its complete remission, this, however, is solely an ephemeral result. As soon as cortisone application is reduced or suspended, there is usually a “rebound” effect where the psoriasis will reappear, often more acutely than before. If the patient continues using cortisone without interruption, there is still a risk of the skin becoming very damaged.
DermaClub recommends using natural reducing agents such as sulfur, salicylic acid, and ichthyol sulfonate.
For plantar psoriasis, use 2S Cream in the evening and PEG Ointment the following morning. For every application, apply a small amount of each product and massage well. For best results, it is also necessary to stop washing or wetting the feet because every washing is an irritating moment for Psoriasis. To keep the feet sanitised without washing them, dry cleaning with a potassium permanganate solution is used as explained in the specific article.
For PPP, substitute 2S Cream for Dermictiol Cream in the evenings and continue with PEG Ointment in the morning. For every application, apply a small amount of each product and massage well. During treatment, avoid getting the foot wet.
In cases of nail psoriasis, 2S Cream can be applied on the nail itself, or between the nail and the nailbed. Again, throughout treatment, avoid getting the foot wet. As in most cases of psoriasis, areas of the feet and nails affected with the condition will benefit from responsible sun exposure.

As in most cases of psoriasis, areas of the feet and nails affected with the condition will benefit from responsible sun exposure.