ANSWER: PALMOPLANTAR KERATODERMA
Palmoplantar keratoderma (PPK) is a condition resulting in overproduction of keratin on the palms of the hands and the soles of the feet. PPK can be transmitted genetically as an autosomal dominant disorder, an autosomal recessive disorder, or an X-linked disorder; it can also be acquired as a random genetic mutation.1
PPK is a symptom of a variety of described syndromes, including Papillon-Lefèvre syndrome, Vohwinkel syndrome, and Unna-Thost syndrome, but is directly related to the ichthyosis family of skin conditions.2 The prevalence of PPK is approximately 1 in 250,000; there is no racial or gender predominance.3
Although 40 different types of PPK have been described (under the heading of palmoplantar ectodermal dysplasias), a trait common to all of these is the presence of a thickened epidermal layer in regions of contact friction, such as the ankles, knees, palms of the hands, and soles of the feet. The 3 main classifications of PPK are the diffuse, focal, and punctate forms; these differ in their age at onset and location (Table).3
Each of these 3 types can be further described as epidermolytic or nonepidermolytic. In this patient, PPK manifested early in life—within the first 3 months postpartum—and was localized to the palmoplantar surfaces, with a defined border (arrows). His palms and soles did not have a waxy appearance; this finding distinguished his condition from nonepidermolytic PPK. In addition, the toenail involvement and history of secondary bacterial infection indicated that his condition was more diffuse. Thus, his PPK can be characterized as diffuse and epidermolytic.
Although diagnoses of PPK are usually made on the basis of clinical findings and age at onset, a definitive diagnosis requires confirmation with both biopsy and specific genetic testing. Other entities to consider include ichthyosis, psoriasis, lichen planus, and dyshidrotic eczema. If the process in this child had been unilateral, a similar disorder—unilateral palmoplantar verrucous nevus, which follows the lines of Blaschko—would also have warranted consideration.
Classic epidermolytic PPK is traced to a defect in the keratin-9 gene (KRT9) on chromosome 17q21.4 This keratin gene is responsible for the appropriate heterodimerization of the keratin protein that is found only in the epidermis of the palms and soles. A mutation in the KRT9 gene results in the epidermolytic property of PPK. Nonepidermolytic PPK is associated with a mutation in the type II keratin locus on chromosome 12q11-13 on the keratin-1 gene.
It is notable that all male relatives of every generation on the father's side of the patient's family are affected. The patient's sister and a paternal aunt are also affected, but only mildly. His parents are not consanguineous. Genetic testing identified the mode of transmission in this case as X-linked recessive with variable penetrance.
There is no cure for PPK, and the only treatment available is regular symptomatic therapy. A typical regimen consists of keratolytic agents, such as 40% urea(Drug information on urea) emollient creams, topical vitamin A treatments, and/or oral retinoids. The topical lotions are a combination of urea, glycerin, lactic acid(Drug information on lactic acid), and alpha-hydroxy acids. Daily scrubbings and antibacterial cleansings once or twice a day are mandatory. If epidermal cracks and fissures widen, bacterial overgrowth may result. Bacterial overgrowth should be managed with systemic antibiotics, and coverage for methicillin-resistant Staphylococcus aureus should be considered early.5 In this case, the patient had recently been given clindamycin(Drug information on clindamycin) for a skin infection; however, no skin culture or bacterial sensitivity test results were available.
OUTCOME OF THIS CASE
Over the years, this boy has used a combination of topical and oral treatments, which have diminished the itchiness, dryness, and cracking of his palms and soles. About 1½ years earlier, the entire epidermal layer of the soles of his feet peeled off after a fungal infection. This unusual and atypical occurrence resulted in a marked decrease in the hardened erythematous plaques, rendering them only minimally different in texture from areas of unaffected skin. The hyperkeratosis of the soles has not yet returned to its pre–fungal infection state.