Skin disorders affecting the feet

Skin disorders on the feet can affect the glabrous skin on the dorsal aspects, or the thick skin on the plantar aspects, thereof, or both. Some can affect one foot, and others both of them. These diseases can be inflammatory, genetically inherited, infectious and neoplastic in origin. It is important to identify them and to start treatment early. If not treated, some may lead to severe pain on walking, the inability to wear shoes, and amputation with serious disability.


Introduction
Skin disorders on the feet can affect the glabrous skin on the dorsal aspects, or the thick skin on the plantar aspects, thereof, or both.Some can affect one foot, and others both of them.These diseases can be inflammatory, genetically inherited, infectious and neoplastic in origin.It is important to identify them and to start treatment early.If not treated, some may lead to severe pain on walking, the inability to wear shoes, and amputation with serious disability.

Inflammatory diseases
Inflammatory skin diseases which affect different areas of the body can affect the feet as well.Some of these diseases are briefly discussed.

Chronic eczema
Chronic eczema is one of the most common inflammatory skin diseases, and can affect the feet as well (Figure 1).Hand and foot eczema is just one example.It occurs in patients who tend to sweat a lot on their palms and soles.Tinea pedis must be excluded in these patients.The page number in the footer is not for bibliographic referencing www.tandfonline.com/ojfp35

Reiter's syndrome
Reiter's syndrome is characterised by nonsuppurative polyarthritis, urethritis, cervicitis or enteric infections, particularly in young men carrying human leukocyte antigen B27. 1 Infections such as Chlamydia, Ureaplasma, Shigella and Salmonella spp.are triggering factors.Reiter's syndrome is characterised by a classic triad of arthritis, conjunctivitis and urethritis.Skin manifestations are common.Typically, keratoderma blenorrhagicum (Figure 3) appear on the soles.This usually appears 1-2 months after the onset of arthritis and conjunctivitis, but may accompany or rarely precede the initial manifestations. 1Reiter's syndrome can also occur as a manifestation of immune reconstitution inflammatory syndrome in human immunodeficiency virus (HIV)-infected individuals, and may follow a severe clinical course. 2

Palmoplantar keratoderma
Palmoplantar keratoderma is a group of diseases which mainly affect the thick skin of the soles, but the palms can also be involved.It may be genetically inherited or acquired. 3any hereditary keratodermas have been found to be caused by abnormalities in the structural protein of the epidermal keratinocytes.Hereditary palmoplantar keratoderma can be diffuse, mutilating, punctate or focal, and is characterised by abnormal thickening and hardening of the thick skin of the palms and soles (Figure 4).
Acquired palmoplantar keratodermas may be due to inflammatory dermatoses, like eczema and psoriasis.There have been reports of it occurring as a cutaneous adverse effect of some drugs.According to a recent report, it is likely that palmoplantar keratoderma with pachyonychia is induced by imatinib mesylate.This drug is a tyrosine kinase inhibitor used to treat chronic myeloid leukaemia and gastrointestinal stromal tumours. 4Imatinib mesylate interacts with the downstream molecules of the epidermal growth factor receptor pathways, leading to cutaneous epithelial proliferation. 4 Pachyonychia congenita is a genetically inherited disease characterised by localised areas of hyperkeratosis on the palms and soles, with grossly thickened, wedge-shaped nails. 5 is a progressive disease.Plantar hyperkeratosis causes pain when walking (Figure 5).Treatment with retinoids and keratinolytics may reduce the hyperkeratosis. 5

Ainhum
Ainhum is a word from the Yoruba dialect meaning "to saw".It is a specific type of a painful constriction of the base of a digit, most commonly the fifth toe, with eventual spontaneous digital amputation.It begins with the formation of a fibrous band on the medial aspect of the toe, which progresses to encircle it.This results in arterial narrowing, bone resorption, swelling of the digit, and eventual autoamputation. 6It is thought to be due to an abnormal blood supply to the foot in some patients as an attenuated posterior tibial artery, and an absent plantar arch   and its branches, have been shown on arteriography in different patients. 7Surgical amputation may be required to avoid ongoing pain.

Tinea pedis
Tinea pedis is commonly called athlete's foot.This is infection of the feet or toes with a dermatophyte fungus.Throughout the world, the vast majority of cases are caused by three anthropophillic species, Trychophyton rubrum, T. mentagrophytes and Epidermophyton floccosum. 8aring tight shoes and the resultant maceration of the toe cleft skin predisposes to this condition; initially a web space infection in most cases (Figure 6).Lesions can spread to the plantar aspects and the dorsa of the feet.Itching is a common complaint in warm weather, mimicking foot eczema.
Treatment with topical antifungal agents, like clotrimazole or terbinafine, is effective.Oral terbinafine may be necessary in severe or recurrent infections.

Onychomycosis
Onychomycosis refers to fungal infection of the nail plate.It may affect the toe-or fingernails.The involvement of the proximal and lateral nail folds is called chronic paronychia.Pulse therapy with itraconazole 200 mg orally, twice a day, for seven days a month, is recommended for onychomycosis and chronic paronychia.Mild cases can be treated with topical amorolfine nail lacquer.

Plantar warts
Plantar warts are caused by various serotypes of human papillomavirus (HPV).There may be a single or multiple lesions (Figure 7).It starts as a small shiny papule, and grows to form a sharply defined rounded lesion with a rough hyperkeratotic surface, surrounded by a thickened horny ring. 9te the pinpoint bleeding in the plantar warts If pared with a scapel, the protective horny ring becomes more obvious.Like all warts, they bleed easily if pared too deep.Many small plantar warts may be grouped together to form a mosaic wart.They can be painful on walking and disabling in some patients.Cryotherapy and topical salicylic acid are first-line therapies.Second-line therapies include intralesional bleomycin, imiquimod and 5-fluorouracil. 10cently, there was a case report of recalcitrant plantar warts associated with statin use.Rapid clearance of the warts followed a patient-initiated decision to discontinue the statin medication. 10It is suggested that statins inhibit cholesterol synthesis in keratinocytes, which may lead to impairment in the barrier function and enable HPV to proliferate within the skin. 11

Eumycetoma (Madura foot) and actinomycetoma
Eumycetoma is a chronic, granulomatous infection of the skin, subcutaneous tissue, fascia and bone, caused by true fungi. 12mmonly reported causative fungi include Madurella mycetomatis, M. grisea and Cephalosporium recifei.Organisms are present in the soil and decaying plant matter.Infection is acquired by traumatic inoculation into the skin or subcutaneous tissue.Recently, a case of eumycetoma caused by Paecilomyces lilacinus was reported. 12Clinically, there is unilateral swelling of the foot.Black granules are drained by the sinuses (Figure 8).

Many cases of eumycetoma eventually result in amputation,
especially if there is bone involvement, which often results in pathological fractures and the failure of medical treatment.
Eumycetoma must be differentiated from actinomycetoma, in which yellowish granules are drained by the sinuses (Figure 9).This is caused by Gram-positive filamentous bacteria.The page number in the footer is not for bibliographic referencing www.tandfonline.com/ojfp37 Actinomycetoma usually responds well to treatment, in comparison with eumycetoma.

Pitted keratolysis
Pitted keratolysis is a superficial infection of the soles caused by a species of Corynebacteria, producing circular erosions thereon (Figure 10).It is common in athletes and individuals who regularly use occlusive footwear.Patients experience hyperhidrosis, foot odour and sometimes itching or burning while walking. 13he odour is due to the production of sulphur compounds by the bacteria.Typical lesions are multifocal, cerebriform, and maceration and crateriform pitting, with superficial erosions. 13he pitting is accentuated when the affected skin is water soaked.Pitted keratolysis predominantly affects the pressurebearing areas of the plantar surface of the feet, and is rarely seen on the non-pressure-bearing areas. 14eatment includes topical erythromycin, topical clindamycin, fucidic acid or mupirocin.Hyperhidrosis should be treated with aluminium tetrahydrochloride solution.Regular changing of footwear and socks is essential.

Cutaneous larva migrans
Cutaneous larva migrans, also called "creeping eruption" or "sandworm", is a clinical term for a distinctive cutaneous eruption characterised by creeping or migrating lesions due to the presence of a moving parasite in the skin. 15Causative parasites include Ancylostoma brasiliensis and A. caninum.These are dog or cat hookworms which can penetrate human skin.Infection is acquired by walking barefoot on infected soil, such as the beach. 16It is commonly seen in warm climates such as the south-eastern parts of the USA, South America, Africa, and other tropical areas. 17inically, the larvae cause a non-specific dermatitis at the site of penetration.The larvae may lie quiet for weeks or months, or immediately begin creeping, producing wandering, bizarre, serpentine patterns (Figure 11).Sometimes the lesions are less typical.They can be patchy excoriations secondary to scratching.They sometimes resemble scabies, bacterial skin infections and fungal infections. 16Treatment with albendazole 400 mg orally per day, for three days, is effective.Other treatment modalities include cryotherapy, as well as smearing a thick layer of petroleum jelly on the lesion.This suffocates the parasite and kills it.

Malignant melanoma
The subject of melanomas is clearly beyond the scope of this article.Melanomas are malignant tumours arising from melanocytes. 18e highest incidence rates in the world are found in Caucasians living in Queensland, Australia and New Zealand, with an annual incidence of approximately 40 cases per 100 000 population.The acral lentigenous type typically occurs on the hands or feet, especially on the palms or soles.It is the most common type   Any pigmented lesion suspected of being a melanoma must be referred to a dermatologist as early diagnosis and treatment may improve the prognosis.

Kaposi's sarcoma
Kaposi's sarcoma is another neoplastic disease which is often seen on the limbs, although it can occur anywhere in the body.There are four clinical types, i.e. classic Kaposi's sarcoma, Africanendemic Kaposi's sarcoma, Kaposi's sarcoma associated with other forms of immunosuppression other than HIV, and finally the HIV-associated type.The HIV-associated type is the most common and most aggressive in South Africa.Early lesions may appear as bluish macules and plaques.Late lesions present with massive lymphoedema and multiple nodules (Figure 13).

SouthFigure 1 : 2 :
Figure 1: Chronic eczema on the feet Figure 2: Contact dermatitis due to leather shoes

Figure 6 :
Figure 6: Tinea pedis, with maceration in the web spaces

Figure 8 :
Figure 8: Eumycetoma of the left foot, with black granules being drained by the sinuses

Figure 9 :
Figure 9: Actinomycetoma of the right foot, with yellowish granules being drained by the sinuses