The Role of Trichoscopy in the Preliminary Diagnosis of Immunobollous Diseases

Autoimmune bullous diseases are a variety of skin diseases that are characterized by the presence of bullae or blisters. Most of these diseases are associated with substantial morbidity and mortality. They are classified according to the site of blister formation into intraepidermal as pemphigus valgaris and foliaceus, and subepidermal as bullous pemphigoid and dermatitis herpetiformis. These lesions commonly affect the scalp and manifest as blisters, erosions and crustations.

Pemphigus is a group of potentially life-threatening intraepidermal vesiculobullous autoimmune diseases that affect the skin and mucous membranes. It is characterized by the presence of circulating and tissue-bound autoantibodies directed against desmogleins, which attaches adjacent epidermal cells via desmosomes. When autoantibodies attack desmogleins, the cells become separated from each other and the epidermis becomes "unglued", a phenomenon called acantholysis. This causes blisters that slough off and turn into sores.

In pemphigus vulgaris (PV) blisters and erosions occurs in the skin and/or mucous membranes, and circulating autoantibodies are directed against desmoglein 3 and 1. In pemphigus foliaceus, there is mainly skin involvement and antibodies are exclusively directed against desmoglein 1. Histologically, both subtypes exhibit intraepidermal blister formation with loss of keratinocytes' adhesion. However, in Pemphigus vulgaris, the split occurs just above the basal cell layer, whereas in pemphigus foliaceus it occurs in the upper part of the epidermis, at the level of the granular layer.

Bullous pemphigoid (BP) is a chronic, autoimmune, subepidermal, blistering skin disease that rarely involves mucous membranes. It is characterized by the presence of immunoglobulin G (IgG) autoantibodies specific for the hemidesmosomal BP antigens BP230 (BPAg1) and BP180 (BPAg2). The lesions of BP may initially start as an urticarial eruption, which over a course of weeks to months, develops into bullae. The lesions are usually prurutic. Once formed, blisters are large and tense, with a round or oval shape. Discrete lesions arise on normal or erythematous skin and are scattered throughout the body.

Dermatitis herpetiformis (DH) is an autoimmune blistering disorder associated in most patients with a gluten-sensitive enteropathy (GSE). DH is characterized by pruritic erythematous clusters of multiforme lesions, frequently in herpetiform pattern. Histopathologically, there are neutrophilic micro-abscesses in dermal papillae, dermal infiltration of neutrophils and eosinophils, and the formation of subepidermal vesicles. Blisters form within the lamina lucida.