Volume 39 Number 3

Introduction

Podoconiosis is a form of non-filarial (infectious disease) lymphoedema and is a debilitating chronic swelling of the foot and lower leg. Podoconiosis occurs with long-term exposure to irritant red volcanic clay soil in the highland regions of Africa, Central America and India¹. It is caused by the passage of microparticles of volcanic silica and aluminum silicates through the skin of those walking barefoot in areas with a high content of volcanic soil². Podoconiosis is a non-communicable (no person-to-person spread) tropical disease with high potential for eradication, but it remains a neglected condition.

Globally, it is estimated that there are four million people affected with podoconiosis³. The highest reported prevalence values are in Africa, including 8.08% in Cameroon, 7.45% in Ethiopia, 4.52% in Uganda, 3.87% in Kenya, and 2.51% in Tanzania⁴. In India, the prevalence was estimated to be 0.21%, primarily from Manipur, Mizoram and Rajasthan States⁴. The prevalence is higher in adults compared to children or adolescents, and is likely due to a longer duration of exposure to volcanic soil⁴.

Several risk factors have been implicated in the development of podoconiosis such as a family history of the disease, absence of footwear, poor foot hygiene and low frequency of wearing shoes⁵. Other factors, such as being from a medium income household and having primary education, lower the risk of developing podoconiosis⁵. Studies have shown, however, that even in those with risk factors, podoconiosis develops in only a subgroup of people. One study conducted in Ethiopia found familial clustering, with a high heritability of 63%⁶. A genome-wide scan of 194 cases and 203 controls, alongside family-based testing, demonstrated association between variants in HLA Class II loci with podoconiosis, suggesting that the condition may be a T cell-mediated inflammatory disease⁶.

Social stigma of patients with podoconiosis is widespread. It is, at times, erroneously believed to run in families – which may occur due to the same exposures and not due to person-to-person spread – leading to isolation of those afflicted⁷. However, the diagnosis of podoconiosis is linked with a lower quality of life. Additionally, similar to other chronic illnesses, a recent study identified depression prevalence to be 12.6% amongst individuals living with podoconiosis⁸. Factors associated with this include social stigmatisation, living in an urban area, being illiterate, and being single⁹. Economic losses are also enormous since it mainly affects adults. This leads to reduced productivity and absenteeism, and contributes to the disease–poverty–disease cycle¹⁰. The estimated productivity losses per patient amount to 45% of working days per year, causing a significant economic impact¹¹.

Clinical features

Podoconiosis presents as bilateral asymmetrical lower limb swelling below the knee lasting more than a month, plus any one of the following symptoms – skin itching or burning, foot oedema, lymph ooze (due to build-up and overflow of lymph fluid from the vessels), prominent skin markings, rigid toes and/or mossy papillomata¹² (Figures 1 & 2). Podoconiosis has a curable pre-elephantiasic phase but causes lifelong disability once the elephantiasis phase is established. Progression to chronic disease (incurable state) occurs over years and has five stages (Table 1). Podoconiosis demonstrates changes of chronic lymphoedema with extensive sclerosis (hardening of tissue), loss of elastic fibres, verrucous acanthosis (hyperpigmented and hyperkeratotic plaques), and reactive changes of eccrine structures (destruction of sweat and sebaceous glands)^13,14,15,16.

Figure 1 Podoconiosis with foot and lower limb deformity.

Figure 2: Podoconiosis with gross nodular involvement.

Pathophysiology

Traditionally, it has been identified that silicate particles absorbed via the skin induce an inflammatory process of the lower leg lymphatics. However, more recent work has identified that minerals enriched in incompatible elements such as calcium, potassium, magnesium and sodium are strongly implicated in the development of the disease¹⁴. Persons with dry skin have a greater risk – due to skin cracking or splitting – of particle absorption, lymphoedema and infection¹⁵. Silicate particles entering through skin are then thought to be taken up by macrophages in the lower limb lymphatics, causing subendothelial oedema, lymph inflammation and, eventually, destruction of the lymphatic lumen. In addition, immune cells are activated which contribute to ongoing inflammation. Eventually, these changes lead to clinical lymphoedema. The chronic inflammation transforms the swollen soft tissues to hard and thickened skin over time, contributing to the irreversibility of the condition.

Approach to treatment

Research has shown that the provision of a simple, inexpensive package of lymphoedema self-care has considerable impact on both clinical progression and self-reported quality of life of affected individuals². Several qualitative research studies show that culturally-informed education programmes that increase the perceived controllability of stigmatised hereditary health conditions like podoconiosis have promise for increasing preventative behaviours and reducing interpersonal stigma¹⁷. Additionally, several factors have been described as barriers to preventive behaviour, including uncomfortable footwear for farm activities and sports, affordability of shoe wear, shortage of soap for washing, as well as cultural influences promoting gender inequality which result in women being least able to access shoes¹⁸. As a result, it is essential to link podoconiosis-affected families with local governmental or non-governmental organisations providing socioeconomic support for households so families are able to better engage in behaviours that will reduce the risk of podoconiosis¹⁸. Finally, in order to address the high burden of mental distress among people with podoconiosis, it is essential to integrate psychosocial care into the current morbidity management of podoconiosis¹⁹.

Differential diagnosis

Accurate diagnosis of podoconiosis is essential for appropriate patient management and treatment. The diagnosis is established clinically as there is no gold standard diagnostic tool. It is a diagnosis of clinical exclusion based on history, physical exam, and certain antigen-antibody specific tests to exclude diseases included in the differential diagnosis such as filarial (infectious) lymphoedema and congenital lymphoedema. The differentiating features of filarial lymphoedema, congenital lymphoedema and podoconiosis are detailed below (Table 2).

Conclusion

Podoconiosis is a chronic swelling of the foot and lower leg caused by long-term exposure to irritant red volcanic clay soil in the highland regions of Africa, Central America and India. Those affected by podoconiosis have significant morbidity, loss of productivity, and frequently experience stigma and isolation. As there are simple measures for prevention, the elimination of podoconiosis is feasible. Global and local advocacy efforts for shoe provision and education are therefore urgently needed.

Conflict of Interest

The authors declare no conflicts of interest.

Funding

The authors received no funding for this study.

Author(s)

Merna Adly
MD candidate
Cumming School of Medicine, University of Calgary, Calgary, AB, Canada

Kwadwo Mponponsuo
MD
Department of Medicine, University of Calgary, Calgary, AB, Canada

Ranjani Somayaji*
BScPT, MD, MPH, FRCPC
Departments of Medicine; Microbiology, Immunology & Infectious Disease; Community Health Sciences, University of Calgary, Calgary, AB, Canada
Email rsomayaj@ucalgary.ca

* Corresponding author

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