Hyperkeratosis of the Heels: Treatment With Salicylic Acid in a Novel Delivery System

Joseph Bikowski, MD

Disclosures

Skinmed. 2004;3(6) 

Introduction

A 43-year-old woman presented with dryness and scaling of the lateral and posterior aspects of both heels, which was diagnosed as hyperkeratotic xerosis (Figure 1). Pertinent medical history included dry skin with winter exacerbation and painful hyperkeratosis of the heels present for many years. The patient applied a topical multivesicular cream formulation of 6% salicylic acid (Salex, Healthpoint Ltd., Fort Worth, TX) to one foot b.i.d. The physician was blinded as to which foot was treated. After 2 weeks of treatment, it was apparent that the patient was applying the cream to the right foot, as evidenced by reduced dryness, scaling, and hyperkeratosis (Figure 2). The patient continued treatment of the same foot for an additional 2 weeks, revealing a dramatic improvement of the right heel, which appeared smooth and soft and devoid of pain. No irritation was associated with treatment; the patient commented that this was the best her heel had been "in years." Subsequently, the patient treated both heels with salicylic acid 6% multivesicular cream. A second patient, a 25-year-old woman, was treated for ichthyosis vulgaris and hyperkeratosis of both heels. She presented with multiple painful fissures and hyperkeratosis of the posterior heels bilaterally (Figure 3). After 1 week of topical treatment with salicylic acid 6% multivesicular cream applied b.i.d. to the left heel only, there was rapid resolution of both hyperkeratosis and pain (Figure 4).

Lateral and posterior heels of a 43-year-old woman diagnosed as having bilateral hyperkeratotic xerosis.

Right heel after 2 weeks of treatment with 6% salicylic acid multivesicular cream.

Posterior heels of a 25-year-old woman with ichthyosis vulgaris.

Left heel after 1 week of 6% salicylic acid multivesicular cream treatment.

The stratum corneum has been likened to a brick wall composed of stacked layers of corneocytes (bricks) held together by a lipid-based intercellular matrix (mortar).[1] With at least 10% hydration, the stratum corneum serves as a tough yet flexible protective barrier against excessive water loss due to evaporation and environmental insults. This process is accomplished primarily through systems involving epidermal and sebaceous lipids in combination with proteins, as well as the natural moisturizing factor derived by hydrolysis of filaggrin.[2,3,4] Xerosis is a disorder of the skin characterized by redness, dry scaling, and fissures.[2] In xerotic skin, the structure of the stratum corneum is modified by abnormalities in keratinization, proliferation, surface lipids, water metabolism, pH, and sebum.[5] Ichthyosis vulgaris, the most common form of inherited ichthyosis, is characterized by a deficiency in filaggrin breakdown products.[4,6]

Xerosis can cause cutaneous discomfort and concerns about appearance that may warrant treatment. The goals of treatment include replacing water content and natural skin oils, maintaining skin hydration, providing a soothing protective film, controlling keratinization, and alleviating symptomatology.[6] Treatment with topical retinoids or vitamin D may be effective.[6] The most commonly used therapeutic moisturizers are creams and lotions, both of which use emulsion technology.[1] The two primary active ingredients in topical hydrating therapies are emollients, which act primarily on the skin's surface to form a lipid-based, occlusive barrier that decreases evaporation, and humectants, which attract transepidermal water and theoretically improve hydration of the stratum corneum.[1,3]

The emulsification of these components into a single formulation may enhance the aesthetics and efficiency of the moisturizer.[3] Variations in moisturizer components and emulsification technologies provide products that vary in their hydrating properties and irritation potential.

Keratolytic agents are recommended in patients with xerosis because accompanying hyperkeratosis is common. Keratolytic agents, often formulated in lubricating vehicles, decrease corneocyte adhesion, promoting desquamation of the stratum corneum. Commercially available formulations include hydroxy acids (e.g., lactic acid, glycolic acid), salicylic acid, and urea.[6] Salicylic acid and urea have been widely used as topical treatments for xerosis for nearly 3 decades.[2,7,8]

Salicylic acid is a keratolytic agent that induces corneocyte disaggregation in the upper stratum corneum, thereby enhancing the shedding of scales and softening the stratum corneum.[9] Urea increases water uptake and enhances water-binding capacity in the stratum corneum, exerting its keratolytic effect through the process of denaturing proteins.[8,10] A limitation of the currently available keratolytic topical formulations is their potential to cause such unwanted reactions as stinging, burning, and erythema due, in part, to their rapid absorption and erratic peak-trough concentrations.2.9,11 This new formulation of salicylic acid utilizes a patented multivesicular emulsion technology to control delivery of salicylic acid through the creation of a novel, two-phase, oil-in-water emulsion system. It produces a multivesicular structure containing multilamellar concentric spheres or shells of oil and water. As a result, the salicylic acid, which is primarily trapped in the multivesicular structures, is time-released as opposed to being spike-released.[11]

Such formulation technology is novel in that the emulsion process creates a stand-alone drug-delivery system. An advantage of the multivesicular emulsion delivery system, as compared with other delivery systems, is its controlled release vs. bulk release of oil-solu-ble and water-soluble ingredients. The composition of the multivesicular emulsion itself has also been shown to reduce transepidermal water loss and increase skin hydration due to the inherent moisturization properties of the emulsion base.[11]

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