KELOID AND HYPERTROPHIC SCAR
Keloids are common benign skin tumors that consist of excessive scar tissue that forms after trauma or inflammatory skin conditions such as acne vulgaris. The keloid proliferates uncontrolled and expands beyond the borders of the underlying scar produced by the traumatic event. Hypertrophic scars, on the other hand, are exuberant scar formation that stays within the confines of the original scar border.
Clinical Findings: Keloids are often large over-growths of scar tissue that expand over the original border of the underlying scar and affect previously normal-appearing skin. They may occur anywhere on the body but are more common on the earlobe, chest, and upper arms. They can affect any age group and affect males and females equally. Dark-skinned individuals have a higher incidence of keloid-type scarring. Almost all keloids manifest after a preceding traumatic event such as a cut, ear piercing, burn, or surgical excision. Many other causes have been found to initiate the formation of keloids, including acne lesions and bug bites. Keloids often start as small, red, itchy papules that quickly enlarge into plaques and nodules. They usually have a smooth surface with firm consistency. Itching is a frequent complaint and often precedes the growth stage. Keloids are diagnosed clinically in a patient with the appropriate history. The differential diagnosis of early keloids includes hypertrophic scars. Difficulty sometimes arises when a patient presents with a firm, enlarging plaque or nodule but no preceding history of trauma. In these cases, a biopsy is prudent to rule out a dermatofibrosarcoma protuberans. The histopathological findings easily differentiate the two lesions.
Hypertrophic scars occur after trauma and are confined to the area of the original trauma or scar. Hypertrophic scars, unlike keloids, do not grow into the adjacent normal skin. They can be quite large and often are pink to red in color and pruritic. Hypertrophic scars tend not to reach the size or extent of keloids, and for that reason they are a bit easier to manage therapeutically. Hypertrophic scars are diagnosed clinically in a patient with a typical history of preceding trauma and the characteristic clinical findings.
Pathogenesis: Keloids appear to be more common in dark-skinned individuals during the first 3 decades of life. Keloids may have a genetic pathogenesis that has yet to be discovered. Certain areas of the body are more prone to keloid formation, including the chest and earlobes, and there may be some local skin cytokine profile that allows for their formation. Biological studies have looked at various cytokines, and transforming growth factor-β (TGF-β) has been found in elevated levels in keloids. TGF-β causes recruitment of fibroblasts into the region and induces them to produce more collagen. Local blockade of this cytokine may be developed as a therapy in the future.
Histology: Keloids show an increase in collagen production, and the collagen is arranged in a disorganized fashion. The overlying epidermis is typically thin due to the mass effect of the keloid tumor pressing on the undersurface of the epidermis, which causes attenuation of the surface epithelium. Mucopolysaccharides are found between the collagen fibers.
Hypertrophic scars are smaller and not exophytic in nature, and the collagen bundles are arranged parallel to the epidermis. There may be an increase in mast cells in both hypertrophic scars and keloids.
Treatment: Hypertrophic scars do not need to be treated, because most will eventually flatten and blend with the surrounding skin. Intralesional triamcinolone may be used to help speed the process along, but care should be taken not to inject too much and thereby cause atrophy. Daily massage by the patient has also been shown to be effective in decreasing the outward appearance of the scar. The redness of both hypertrophic and keloid scars can be treated successfully with pulsed dye laser.
Keloids are more challenging to treat. They have a high rate of recurrence after excisional removal, and for this reason adjunctive therapy should always be used after excision. Serial injections with intralesional triamcinolone monthly for 4 to 6 months may help avoid a recurrence after surgery. Postoperative radiation therapy has also been very successful in decreasing the recurrence rate. There are anecdotal reports of treatment with imiquimod and cryotherapy, but they are of questionable value.