Laboratory Studies
The purpose of any investigation is to search for underlying causes, particularly causes of pruritus.
Urea and creatinine determinations are needed to detect any underlying renal impairment. A creatinine clearance test and other more complex renal investigations may be required.
Ferritin levels and a full blood cell count can help detect anemia. Low iron stores can cause pruritus.
Random glucose testing can help detect diabetes.
Skin biopsy is essential to make a diagnosis.
Histologic Findings
The histology varies with the stage of the reactive perforating collagenosis. Early lesions show epidermal hyperplasia associated with underlying degenerate basophilic collagen fibers. In established lesions, a cup-shaped depression of the epidermis associated with a keratin plug containing parakeratosis, inflammatory debris and collagen fibers can be seen.
(See the image below.)
Cup-shaped invagination of the epidermis associated with a keratin plug containing inflammatory debris and collagen fibers.
Vertically orientated basophilic collagen fibers are seen in the underlying dermis, with focal extrusion through the epidermis.
Vertically orientated collagen fibers are extruded into the overlying keratin plug.
The epidermis is atrophic and may show ulceration. However, at the edges of the cup-shaped invagination, the epidermis is hyperplastic. Additionally, a mild perivascular lymphohistiocytic infiltrate can be seen.
Extruded collagen fibers may be demonstrated with elastic van Gieson (EVG) staining, which stains the fibers red. No extrusion of elastic fibers should be seen (staining black with EVG).
An elastic van Gieson stain demonstrating the expulsion of collagen fibers (red) into the overlying keratin plug.
-
Typical keratotic papules.
-
Cup-shaped invagination of the epidermis associated with a keratin plug containing inflammatory debris and collagen fibers.
-
Vertically orientated collagen fibers are extruded into the overlying keratin plug.
-
An elastic van Gieson stain demonstrating the expulsion of collagen fibers (red) into the overlying keratin plug.
