Palmoplantar keratoderma (PPK) is a large group of conditions with the consistent core feature – hyperkeratosis of the palms and soles of the feet. Despite being a broad group of conditions, it is generally uncommon, although most practising podiatrists will have a patient or two in their caseload with the condition in one form or another.
PPK, for the most part, represents a group of sporadic (non-hereditary) causes. Aetiologies for these include:
· Drug-related
· Malnutrition
· Infections
· Dermatological disease
· Paraneoplastic
· Keratoderma climactericum
· Idiopathic
A small number of cases are attributable to specific genes and consequently are hereditary with varying patterns of inheritance. Typically, these are differentiated from sporadic cases by their early onset and positive family history (1). Around 45 genes to date have implicated in these hereditary cases. Predominantly these mutations affect the quality and amount of keratin produced although many sub-types affect other aspects of cellular apposition and structure or cell signalling such as water channels, desmosomes, gap junctions and intermediate filaments of the skin which can manifest clinically in similar ways to keratin mutations. Clinically many types of hereditary PPK exist and are documented by the Genetic and Rare Diseases Information Center (https://rarediseases.info.nih.gov/) with an array of differing symptoms affecting many systems.
For many patients, their quality of life is severely affected, and pain is often a significant feature of the disease. Pain can arise from the mechanical aspects of the disease – corns, callus, blistering and fissuring or be related to altered sensory pain pathways as a result of keratinocyte signalling malfunction or disease-associated neuropathy (2).
In the podiatry clinic, the mainstay of treatment for many of these patients is regular debridement and reduction of painful lesions accompanied by the use of topical moisturisers to soften hardened areas of skin. In the British Journal of Dermatology a recently published report has undertaken an exhaustive review of published literature, to give some insight into the current state of knowledge regarding the treatment of PPK. The review looked at all papers published since 2008 which covered any aspect of treating a patient (or patients) diagnosed with any form of PPK. They used multiple databases to ensure they captured a wide range of literature sources.
Ultimately, this returned just 42 papers. The majority were of a low level of evidence – case-control studies, case reports and case series. The authors then went on to review topical and oral treatments. Topically, the majority of work focussed on mechanical debridement, use of moisturising techniques or keratolytics (to dissolve excess skin). Despite mechanical debridement being frequently mentioned as a form of treatment, it remains formally untested in the literature. Likewise, the moisturizing regimes including the use of regular emollients, urea-based products, sodium lactate and propylene glycol used in conjunction with salicylic acid remain reported and observed but not fully tested. The use of orthotics and insoles also is briefly mentioned in conjunction with footwear but without significant detail.
Systemic treatments have developed in the last few decades with a greater range of drugs available for use. Oral retinoids such as isotretinoin and acitretin) have been used for many years with some success but risk side-effects (teratogenicity, drying of mucous membranes, elevated cholesterol and headache). A newer retinoid, originally developed for hand eczema, alitretinoin, has shown in a few cases to be more tolerable with a lower risk of side effects. The effectiveness of the drugs primarily depends on the particular type of PPK being treated. Where sweating is a problem, the use of measures such as iontophoresis has been found to be helpful, along with botulinum toxin.
Overall, the paper provides a good overview of the current state of knowledge for the management of this condition. Unfortunately, the state of knowledge is very limited and for the most part, there is no evidence of effectiveness other than the case reports identifying the use of various treatments in a few patients without proper comparisons.
References
1. Has C, Technau-Hafsi K. Palmoplantar keratodermas: clinical and genetic aspects. JDDG: Journal der Deutschen Dermatologischen Gesellschaft. 2016;14(2):123-40.
2. Weinberg RL, Coulombe PA, Polydefkis M, Caterina MJ. Pain Mechanisms in Hereditary Palmoplantar Keratodermas. Br J Dermatol. 2019;182(3):543-51.