Pain mechanisms in hereditary palmoplantar keratodermas

Background: Palmoplantar keratodermas (PPKs) are a heterogeneous group of skin disorders characterized by thickening of the epidermis on the palms of the hands and soles of the feet. Individuals with PPKs report varying degrees of palmoplantar pain that can severely affect quality of life. Objectives: To provide an overview of the scope of pain in hereditary PPKs and highlight candidate mechanisms underlying this pain. Methods: In this review, we discuss several forms of hereditary PPKs, with a focus on the incidence, nature, candidate underlying mechanisms and treatment of pain in these conditions. We also synthesize this information with current understanding of the mechanisms contributing to pathological pain in other conditions. Results: Pain is a major problem for many, but not all individuals with hereditary PPK. This pain remains poorly understood, inconsistently reported and inadequately treated. The heterogeneity of pain prevalence and presentations across the many forms of PPK suggests that there may exist corresponding heterogeneity in the cellular and molecular mechanisms that drive and shape PPK-associated pain. Some candidate mechanisms include structural (e.g. fissures and blisters), infectious and immune/inflammatory processes. However, a growing body of evidence also supports the occurrence of localized neuropathic alterations in the affected skin of individuals with PPK, which might contribute to their pain. Conclusions: Greater understanding of these diverse mechanisms may provide a rational basis for the development of improved and targeted approaches to prevention and treatment of pain in individuals with PPK. What's already known about this topic?. Pain is a prominent symptom in hereditary palmoplantar keratodermas (PPKs). Pain in patients with PPK can be difficult to treat. Pain mechanisms in PPKs are poorly understood. What does this study add?. This study defines multiple potential sources of pain in PPK, including both structural lesions (fissures, blisters) and specific cell types. This review highlights the variability of pain among several forms of hereditary PPK. This study provides mechanistic insights into how neuropathic and inflammatory mechanisms might contribute to pain in some forms of PPK.