A geochemical skin disease

Podoconiosis, also known as non filarial elephantiasis, is a disease of the lymphatic vessels of the lower extremities that is caused by chronic exposure to irritant soils. It is the second most common cause of tropical lymphedema after lymphatic filariasis, and it is characterized by prominent swelling of the lower extremities, which leads to disfigurement and disability.

In endemic areas, podoconiosis is a considerable public health problem with severe social, psychological and economic implications. Despite being widespread and the lifelong disability it causes in affected individuals, research into the disease has been scarce and the pathogenesis is partly unclear. A better understanding of the pathogenesis might lead to new prevention and treatment opportunities.

What causes Podoconiosis

Podoconiosis is a form of lymphoedema that occurs in tropical highland areas in genetically susceptible individuals who are exposed to irritant volcanic soils. Though, Podoconiosis is limited to people living and working barefoot who have been exposed from early childhood, over many years, to irritant volcanic soils, such as subsistence farmers, gold miners, weavers and potters, the risk extends to any profession or activity in which there is prolonged contact with irritant soils. The disease causes bilateral asymmetrical swelling of the lower legs.

Podoconiosis affects people who live and work barefoot and cannot afford shoes, such as subsistence farmers. It causes physical impairments, stigmatization and inability to work, imposing a social and economic burden in already marginalized communities, and yet the disease can easily be prevented by encouraging the use of appropriate footwear.

The cause of podoconiosis is likely a combination of genetic susceptibility and long-term exposure to irritant soil.

Photo: volcanic red clay soil.

Where is Podoconiosis found

Podoconiosis is mostly found among the world’s poorest, remote and underprivileged populations in tropical and subtropical areas, particularly in African countries. Globally, podoconiosis affects an estimated 4 million people in 32 endemic countries, many of which are in the highlands of tropical sub-Saharan Africa, but also in parts of Central and South America and South East Asia.

In Africa, podoconiosis has been reported in Angola, Burundi, Cameroon, Cape Verde, Chad, the Democratic ­Republic of Congo, Equatorial Guinea, Ethiopia, Kenya, Madagascar, Mozambique, Niger, Nigeria, Rwanda, Sao Tome and Principe, Sudan, Tanzania and Uganda; in Latin America, in Brazil, Colombia, Costa Rica, Ecuador, El Salvador, French Guiana, Guatemala, Honduras, Mexico, Peru and Suriname; and in Asia, in India, Sri Lanka and Indonesia.

The countries with the highest reported regional prevalence are Ethiopia, Cameroon and Uganda. In Ethiopia, an estimated 1.5 million adults are affected and a further 35 million people are at risk. Equally, in Rwanda, despite a relatively low prevalence, podoconiosis is widely distributed throughout the country.

Image: geographical distribution of Podoconiosis.

What are the symptoms of Podoconiosis

Podoconiosis is characterized by a prodromal phase before elephantiasis sets in. The majority of people develop signs and symptoms of the disease in the second or third decade, but prevalence increases up to the sixth decade. Early symptoms commonly include itching of the skin of the forefoot and a burning sensation in the foot and lower leg.

Early, symptoms are widening of the forefoot with slight swelling and separation of toes, plantar oedema with slight lymphatic oozing onto the skin attracting the characteristic presence of flies, increased skin markings, hyperkeratosis, the development of a mossy foot (papillomatous skin) and “block” toes (toes resemble sausages, lacking their usual curvature).

As the disease progresses over the years, the chronic irreversible stage sets in. The symptoms can vary from a predominantly soft, squashy and lymphedematous type (referred to as “water-bag”) to the thickened, leathery, fibrotic type often accompanied by multiple hard skin nodules and is referred to as elephantiasis. Many patients show a combination of these two variants.

Nerve impairment, loss of sensation in the feet, neuropathic ulcers, involvement of the hands, and a number of characteristic skin changes will also be noticed in some cases of podoconiosis.

Photo: lymphedema associated with genetic susceptibility and barefoot exposure to particulates in volcanic soil.

How can Podoconiosis be prevented

Podoconiosis can be prevented primarily by avoiding or minimizing exposure to irritant soils by wearing shoes or boots and by covering floor surfaces inside traditional huts.

Secondarily, daily foot-washing with soap, water and antiseptic, use of a simple emollient, bandaging in selected patients, elevation of the leg, controlled exercises, and use of socks and shoes will also prevent disease.

How is Podoconiosis diagnosed

Podoconiosis is a clinical diagnosis, relying on recognition of typical clinical features in the correct geographical context. Diagnosis is mainly based on location, history, clinical findings and absence of microfilaria or antigen on immunological card tests. Podoconiosis occurs in populations living at high altitudes about 1000 metres above sea level.

Disease starts in the foot and progresses up the leg to the knee but rarely involves the groin; conversely, lymphatic filariasis is found at lower altitudes and changes often are noticed first in the groin.

Finger-prick blood samples can be used to test for circulating filarial antigen using immunochromatographic card tests; an additional blood sample can be taken for filarial antibody testing. However, both tests may become negative in patients with chronic manifestations of lymphatic filariasis.

How is Podoconiosis treated

Once the disease has developed, rigorous foot hygiene including daily washing with soap and water, application of an emollient, and nightly elevation of the affected extremity has been shown to reduce frequency of acute attacks. Nodules will not resolve with these conservative measures, although surgical removal of the nodules can be performed.

More radical surgery is no longer recommended since patients unable to scrupulously avoid contact with soil experience recurrent swelling which is more painful than the original disease because of scarring. Social rehabilitation is vital, and includes training treated patients in skills that enable them to generate income without contact with irritant soil.

Edited by: Himanshu Arvind Kapadia

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