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Published on: November 29, 2024
Histopathological differential diagnosis of keloid and hypertrophic scar
Julia Yu-Yun Lee1, Chao-Chun Yang, Sheau-Chiou Chao
1Department of Dermatology, National Cheng Kung University Hospital, 138 Sheng-Li Rd, Tainan, Taiwan. yylee@mail.ncku.edu.tw
Insights
Differentiating hypertrophic scars from keloids can be challenging. This study identified key histological features, beyond keloidal collagen, to improve keloid diagnosis, especially when collagen is not apparent.
Area of Science:
- Dermatopathology
- Scar Histology
- Tissue Differentiation
Background:
- Histopathological differentiation between hypertrophic scar (HS) and keloid is often difficult.
- Key markers like keloidal collagen and alpha-smooth muscle actin (alpha-SMA) have limitations in distinguishing these scar types.
- Keloidal collagen is not always detectable, and alpha-SMA expression is variable in both HS and keloid.
Purpose of the Study:
- To identify additional histological features that aid in differentiating keloid from hypertrophic scar.
- To evaluate the diagnostic utility of specific features in keloid specimens, particularly those lacking detectable keloidal collagen.
Main Methods:
- Comparative histological analysis of 40 keloid and 10 hypertrophic scar specimens.
- Assessment of various histological features, including epidermal flattening, papillary dermis scarring, collagen type, vascularity, fibrous fascicle arrangement, and specific band-like structures.
- Evaluation of alpha-smooth muscle actin (alpha-SMA) expression in both scar types.
Main Results:
- Features more common in keloids included: non-flattened epidermis, non-scarred papillary dermis, keloidal collagen, absent prominent vertical vessels, disorganized fibrous fascicles, tongue-like advancing edges, horizontal cellular fibrous bands, and prominent fascia-like bands.
- Tongue-like advancing edges, horizontal cellular fibrous bands, and fascia-like bands were exclusive to keloid specimens, even those without detectable keloidal collagen.
- Keloidal collagen was present in 55% of keloids; alpha-SMA was found in 70% of HS and 45% of keloids, rendering it non-discriminatory.
Conclusions:
- Histological features such as a non-flattened epidermis, non-fibrotic papillary dermis, tongue-like advancing edge, horizontal cellular fibrous band, and fascia-like band are valuable for diagnosing keloids, especially when keloidal collagen is absent.
- These additional features improve the diagnostic accuracy for keloids beyond the presence of keloidal collagen alone.
- Alpha-SMA is not a reliable marker for differentiating between hypertrophic scars and keloids.
Abstract:
Distinguishing hypertrophic scar (HS) from keloid histopathologically is sometimes difficult because thickened hyalinized collagen (keloidal collagen), the hallmark of keloid, is not always detectable and alpha-smooth muscle actin (alpha-SMA), a differentiating marker of HS, is variably expressed in both forms of scar. The aim of this study was to investigate additional distinguishing features to facilitate differentiation between keloid and HS. We compared various histologic features and the expression of alpha-SMA in 40 specimens of keloid and 10 specimens of HS. The features more commonly seen in keloids were: (a) no flattening of the overlying epidermis, (b) no scarring of the papillary dermis, (c) presence of keloidal collagen, (d) absence of prominent vertically oriented blood vessels, (e) presence of prominent disarray of fibrous fascicles/nodules, (f) presence of a tongue-like advancing edge underneath normal-appearing epidermis and papillary dermis, (g) horizontal cellular fibrous band in the upper reticular dermis, and (h) prominent fascia-like fibrous band. The last three features were found in keloid specimens only, including the ones lacking detectable keloidal collagen. Our study confirmed the diagnostic value of keloidal collagen, but it was only found in 55% of keloid specimens. Alpha-SMA expression was found in both HS (70%) and keloid (45%), thus it would not be a differentiating marker. In scars with no detectable keloidal collagen, the presence of the following feature(s) favors the diagnosis of keloid: non-flattened epidermis, non-fibrotic papillary dermis, a tongue-like advancing edge, horizontal cellular fibrous band in the upper reticular dermis, and prominent fascia-like band.
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