Abstract
Introduction
Dyschromic hypertrophic scar (HTS) with areas of hyper- and hypo-pigmentation is a common sequelae of burn injury. The mechanism behind the development of dyschromia has not been elucidated. In this study, we provide a histological analysis of these scars with a focus on rete ridge presence. Rete ridges occur in epithelial tissues such as oral mucosa and skin and can be described as undulating “pegs” that are interdigitated with dermal papillae. Rete ridges enhance adhesion of the epidermis to the dermis. We hypothesize that rete ridge presence is important for normal skin physiology, and their absence or presence may hold mechanistic significance in post-burn HTS dyschromia.
Methods
Subjects with post-burn dyschromic HTS were consented and enrolled (n=27). Punch biopsies of hyper-, hypo-, and normally pigmented scar and skin were collected and stored in formalin. Biopsies were paraffin embedded, sectioned, stained with H&E, and imaged. The number of rete ridges were investigated by calculating a rete ridge ratio from the length of the basement membrane and the length of the epidermis.
Results
The patient population was predominantly female (55.5%), black (70.4%), and had Fitzpatrick skin Type V (51.9%). The injuries were primarily as a result of flame (37%) and scald (33.3%) and resulted in a median TBSA burn of 7%. The median age of the scar at the time of sample acquisition was 12.2 months. The rete ridge ratio of normally pigmented, un-injured skin was above 1 (1.31 ± 0.04), indicating that normal skin’s basement membrane is longer than its epidermal length due to the presence of rete ridges. HTSs resulting from burn wounds that healed without split thickness autografts were first investigated. The number of rete ridges was higher in normal skin compared to HTS that was either hypo- or hyperpigmented (1.31 ± 0.04 vs. 1.13 ± 0.05 and 1.14 ± 0.04 vs, p< 0.05). This difference was similar despite pigmentation phenotype. When hyper-pigmented scars resulting from wounds that were treated with split thickness autografts (Hyper(+)) were investigated, rete ridge number was significantly higher than in Hyper(-) (1.89 ± 0.23, p< 0.01). Patient age showed a weak correlation (R=-0.33) with rete ridge ratio where older patients had lower rete ridge ratios in normal, un-injured skin. Hyper(+) showed a weak correlation between rete ridge ratio and age of scar (R=-0.38).
Conclusions
Post-burn HTS that is dyschromic has fewer rete ridges than normal skin. This finding may explain the decreased epidermal barrier function that is associated with HTS.
Normal skin and hypertrophic scar fibroblasts differentially regulate collagen and fibronectin expression as well as mitochondrial membrane potential in response to basic fibroblast growth factor
