Pigmented purpuric dermatoses (PPD) encompass a cluster of skin disorders marked by petechial hemorrhage resulting from capillaritis. PPD are considered relatively uncommon but can affect individuals of all ages, including children [1,2]. Schamberg disease (SD) is the predominant variant observed in both adults and children [3].

The pathogenesis of PPD is not completely understood, and it may vary among the different subtypes. However, common features include inflammation and hemorrhage of superficial papillary dermal vessels, primarily capillaries. Studies suggest an immunologic event involving cell adhesion molecules (CAM) like leukocyte function adhesion 1 (LFA-1), endothelial leukocyte adhesion molecule 1 (ELAM-1), and intercellular adhesion molecule 1 (ICAM-1), indicating a cell-mediated hypersensitivity reaction [4]. The perivascular inflammatory infiltrate includes CD4+ T cells and CD1a+ dendritic cells. Cytokines produced by leukocytes may induce CAM expression, affecting fibrinolytic activity and causing intravascular fibrin deposition observed in PPD [4,5]. Capillary dilation and fragility, possibly attributed to altered function of blood vessel structure cells like fibroblasts and endothelial cells, may lead to red blood cell leakage, triggering an immune response (Figure 1). Another emerging theory suggests PPD may represent an epitheliotropic T-cell alteration, supported by observations of epidermotropism or a monoclonal pattern in the inflammatory infiltrate [6]. Progression to mycosis fungoides has been reported, emphasizing the need for integrated clinical, molecular, and histopathologic assessments for accurate diagnosis and management decisions [7,8].

Despite clinical variations, all PPD share common histopathological features, including blood vessels dilation, swelling of the endothelial cells, perivascular lymphocytic infiltration, erythrocytes extravasation, and hemosiderin-filled macrophages (Figure 2). Those features are common in all PPD, with distinctions in intensity noted in certain subtypes. Hemosiderin deposits in the superficial dermis, discerned through Perl’s and Fontana-Masson staining, differentiate PPD from stasis dermatitis [9,10]. The infiltrate predominantly consists of CD4+ lymphocytes, occasional CD1a+ dendritic cells, and macrophages [11]. Plasma cells and neutrophils may be present, with the latter observed in itching purpura lesions, such as eczematoid purpura of Doucas and Kapetanakis [11]. Mild epidermal spongiosis and lymphocytic exocytosis are common in all variants except lichen aureus, which typically shows a band-like infiltrate separated from the epidermis by a thin rim of uninvolved collagen (Grenz area) [12]. This infiltrate is also seen in pigmented purpuric lichenoid dermatosis of Gougerot and Blum [13]. A rare variant of granulomatous PPD with a superimposed hemorrhagic granulomatous infiltrate has been described as well [14]. Positive direct immunofluorescence may reveal the deposition of fibrinogen, IgM, and/or C3 in superficial dermal vessels [9]. In addition to confirming the diagnosis of pigmented purpuric eruption, a skin biopsy serves as a valuable tool for ruling out cutaneous T-cell lymphoma, especially in its early stages, as it can mimic PPD both clinically and histologically [8]. Besides a skin biopsy, it is advisable to undergo a blood test to exclude autoimmune disorders, thrombocytopenia, clotting abnormalities, and chronic infections, including HBV and HCV hepatitis [3].

Examining pigmented purpuric dermatoses (PPD) through dermoscopy unveils unique characteristics facilitating their diagnosis. In PPD dermoscopy, a base coloration ranging from reddish-brown to orange is evident, mirroring the underlying hemosiderin deposition. Red dots and globules, corresponding to dilated capillaries and extravasated red blood cells, are commonly observed, contributing to the characteristic purpuric appearance. Moreover, a network pattern in shades of yellowish-brown, reminiscent of branched vessels, may be discerned, underscoring the vascular nature inherent to these dermatoses [15]. Less common features include brown or red circles, grey dots, serpentine or thick linear vessels, as well as rosette structures [16] (Figure 3).

The differential diagnosis for pigmented purpuric dermatoses (PPD) includes several skin conditions that may share similar clinical or histopathological features, particularly involving the lower extremities. Prominent entities include drug hypersensitivity reactions, with potential involvement of specific medications like carbamazepine and nitroglycerine. Purpuric contact dermatitis to clothing is characterized by lesions confined to areas in contact with clothing, accompanied by intense itching, often associated with materials like wool and coloring agents. Venous stasis purpura manifests with signs of chronic venous insufficiency, including swelling, varicose veins, and venous ulcers. Other considerations encompass conditions such as purpura due to thrombocytopenia, senile purpura in the elderly, purpuric exanthema attributed to viral infections, leukocytoclastic vasculitis, IgA vasculitis (Schönlein-Henoch purpura) observed commonly in pediatric cases, Kaposi sarcoma affecting elderly or immunosuppressed individuals, and purpuric mycosis fungoides [3,10].

Five classic subtypes of PPD include: progressive PPD (Schamberg disease), pigmented purpuric lichenoid dermatosis of Gougerot and Blum, lichen aureus, purpura annularis telangiectodes (Majocchi disease), and eczematoid purpura of Doucas and Kapetanakis (Figure 4) [3,17]. Other less common variants include Hersch and Schwayder’s linear unilateral form of PPD (distinct from linear variants of Schamberg disease and lichen aureus) [18], quadratic form described by Higgins and Cox [19], itching purpura of Loewenthal (sometimes considered as a symptomatic variant of SD affecting adults) [20], granulomatous PPD [14], and familial PPD [21]. Furthermore, a transient, estrogen-dependent variant of PPD, called angioma serpiginosum, has been documented in the literature [22].