Table of Contents
Introduction
The process of healing a wound is dynamic and requires proper control. When this equilibrium is upset, unwanted scars like keloids and hypertrophic scars can appear. Because of the increased production of collagen and fibrinogen during the healing process, both types of scars are firm and elevated. They can be symptomatic, frequently resulting in discomfort, movement limits, pruritus (itching), and cosmetic deformity.
Despite their similarities, there are clear distinctions between keloids and hypertrophic scars. While keloids grow outside the original boundaries of the injury and do not regress, hypertrophic scars are limited to the site of the injury and may do so over time. Histologically, keloids show no discernible pattern of collagen, but hypertrophic scars usually show a wavy, regular pattern of collagen.
What Are Keloid and Hypertrophic Scars?
Excessive scar formation results in a firm, smooth, and hard growth known as a keloid scar. Keloid formation usually follows a skin injury, but it can sometimes happen on its own without a serious prior injury. Keloid development is more common in the upper chest, shoulders, neck, and ears; however, it can appear anywhere on the body and spread beyond the original wound margin.
In contrast to keloid scars, hypertrophic scars are limited to the site of skin injury. They frequently appear due to severe tension on a healing wound, leaving a thicker-than-normal scar. While keloids tend to persist and might be more difficult to cure, hypertrophic scars are more likely to retreat and disappear with time.
What Is the Etiology of Hypertrophic and Keloid Scar Formation?
Hypertrophic and keloid scars are skin injuries deep enough to impact the dermal layer. They may appear following surgery, burns, bites from insects, tattoos, chickenpox or acne, and piercings. The specific mechanism of formation of these scar formations is unknown. Hypertrophic scars and keloids are thought to be more likely to occur in patients with systemic inflammation, and diseases that raise systemic inflammatory indicators may further enhance this risk. According to some research, sex hormones may impact the chance of keloid formation by elevating inflammation and causing an excess of collagen to be produced. Furthermore, although a clear causal relationship has not been proven, people with hypertension (high blood pressure) have been shown to have a higher incidence and size of keloids.
What Are the Histological Findings of Keloid and Hypertrophic Scars?
Several histological characteristics aid in differentiating keloids from other forms of scarring. Compared to normal scar tissue, keloid scar tissue has a higher concentration of mast cells (immune cells). Keloids are characterized by a thicker epidermal layer, partly due to increased keratinocytes (skin cells) in the epidermis. Keloid tissue lacks the distinguishing features of the reticular and papillary layers found in normal dermal tissue. In contrast to hypertrophic scars and regular scar tissue, keloid tissue has an abundance of collagen structured in whorls or a chaotic pattern. In addition, keloid cells show an elevated type I to type III collagen ratio compared to normal skin tissue, with both collagen forms being more abundant in keloid scar tissue.
Histologically, flattened epidermis and enlarged collagen fibers arranged parallel to the dermis are the hallmarks of hypertrophic scars. There is clear scarring in the reticular and papillary dermis, and the blood vessels in these scars are oriented vertically. Compared to keloids, hypertrophic scars have finer collagen fibers and a higher percentage of type III collagen than type I collagen. In contrast to keloids, hypertrophic scars express alpha-smooth muscle actin and have myofibroblasts.
What Are the Key Differences Between Keloid and Hypertrophic Scars?
There are some important differences between keloids and hypertrophic scars.
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Hypertrophic scars form within the original wound site and usually start to form a month or two after the injury and expand for several months. They eventually start to get smaller after a year or so. Due to the surrounding tissues' shrinking, these scars, which can have a paler pink or red appearance, impede joint movement. More often, hypertrophic scars can appear anywhere on the body, especially where wounds are infected, inflamed, or left untreated or where joints allow the skin to move.
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Keloids grow outside of the initial wound site; they frequently start to grow several months or years after the injury and do not get smaller with time. Keloids do not affect joint movement and are typically a darker purple-red shade. They are less frequent than hypertrophic scars and usually appear on specific body parts like the cheekbones, earlobes, and upper chest.
What Is the Treatment for Hypertrophic and Keloid Scar?
In general, hypertrophic scars respond better to treatment than keloids and may be cured itself. On the other hand, keloids frequently resist treatment and continue without spontaneous remission. The goals of treatment are to lessen the functional impairments and esthetic deformity caused by keloids, as well as to lessen pain and itching. For some patients, a few interventions have been beneficial, such as:
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Regularly applying emollient oils and lotions to the body.
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Intralesional corticosteroid injections are repeated every few weeks.
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Polyurethane or silicone scar reduction patches.
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Silicone gel.
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Topical or oral Tranilast (an inhibitor of collagen synthesis).
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Superficial X-ray treatment (administered within 48 hours after surgical excision).
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Pressure dressings and garments.
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Surgical excision (in the case of keloids, may leave a new keloid even bigger than the first one).
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Botulinum toxin injections.
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Intralesional 5-fluorouracil.
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Cryotherapy (extreme cold is used to freeze and eliminate abnormal tissue).
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Skin needling (pricking the skin with tiny needles for new collagen formation).
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Superficial X-ray treatment (administered within 48 hours after surgical excision).
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Pulsed dye laser (procedure for getting rid of various vascular abnormalities on the skin, also known as birthmarks).
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Steroid-impregnated tape.
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Subcision (a process that removes scars that have embedded themselves in deeper tissue).
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Retinoic acid.
Conclusion
Hypertrophic and keloid scars are harmless and do not transform into skin cancer. However, patients with keloids have a slightly higher risk of developing skin cancer compared to non-keloid individuals. Despite not being harmful to general health, hypertrophic scars and keloids can be uncomfortable and cause mental distress because of how they affect appearance. Keloids may disappear over time, but hypertrophic scars usually do not. Because of the variety of available treatments, it is recommended that dermatologists and maybe plastic surgeons be included in the multidisciplinary team that manages these disorders.
