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Chapter 10: Immunodermatology

LIM Yen Loo; JHINGAN Anjali; TANG Boon Yang Mark; WANG Cho Ee Etienne; TEO Wan Lin

INTRODUCTION

Immunodermatology is an integral aspect of medical dermatology that encompasses a wide range of immune-mediated skin disorders. These include immunoblistering diseases, cutaneous lupus, vasculitis, and skin manifestations of systemic connective tissue diseases.

IMMUNOBLISTERING DISEASES

The skin is intricately built as a physical barrier (Figures 10–1, 10–2, 10–3, 10–4, 10–5, 10–5a, 10–6, 10–7, 10–8, 10–9, 10–10, 10–11, 10–12, 10–13, 10–14, 10–15, 10–16, 10–17, 10–18, 10–19, 10–20, 10–21, 10–22, 10–23, 10–24, 10–25). This barrier function is brought about by cell-cell adhesions between keratinocytes in the epidermis, and between the basal keratinocytes and the basement membrane. When these adhesions are disrupted, blisters or erosions ensue. In general, immunoblistering diseases are classified as either intraepidermal or subepidermal based on the level of disruption of these cell adhesions.

Figure 10-1

Pemphigus vulgaris

Pemphigus vulgaris (PV) is a blistering disorder with autoantibodies directed against desmogleins (Dsg) that form the desmosomes between keratinocytes. Disruption of desmosomal adhesion leads to blistering within the epidermis, which results in flaccid bullae and erosions. Treatment usually requires high-dose systemic corticosteroids and immunomodulatory medications like azathioprine, mycophenolate mofetil, intravenous immunoglobulin therapy, or intravenous rituximab.

A patient with pemphigus vulgaris exhibits multiple large, dark, crusty blisters, some open red lesions, and flaccid bullae on the back and upper arms.
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Figure 10-2

Pemphigus vulgaris—histology

The histology shows a suprabasal split containing a few inflammatory cells. The keratinocytes display the characteristic feature of acantholysis due to loss of intercellular adhesion. Acantholytic cells lie freely within the blister cavity and form a lining of intact basal cells (so-called row of tombstones) along the blister floor. A variable infiltrate of lymphocytes and eosinophils may be present in the underlying dermis.

A micrograph shows acantholytic keratinocytes within the cavity of a blister, and tiny blue cells of inflammatory infiltrate in the dermis.
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Figure 10-3

Pemphigus vulgaris—DIF

Direct immunoflourescence (DIF) shows an apple-green fluorescence with a fish-net pattern in the lower epidermis, with positive staining for intercellular IgG (pictured) and C3 deposits, corresponding to the location of desmosomes and the distribution of the desmogleins, the intercellular antigenic sites.

A micrograph shows apple-green fluorescence in the epidermal layer, indicating the presence of intercellular I g G.
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Figure 10-4

Pemphigus vulgaris—mucous membrane involvement

Painful oral erosions or ulcers may precede the appearance of cutaneous lesions or be the only manifestation in PV. Patients with mucosal PV have autoantibodies to desmoglein 3 and those with mucocutaneous PV have autoantibodies to both desmoglein 3 and desmoglein 1. Mucous membranes have a higher proportion of desmoglein 3 compared to desmoglein 1. This explains the lack of mucosal involvement in patients with pemphigus foliaceous (PF), where only antibodies against desmoglein 1 are present.

A patient with pemphigus vulgaris exhibits glossy, white ulcerations on the inner mucosa of the lower lip.
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Figure 10-5

Pemphigus foliaceous

PF presents as erosions and crusts, mainly in the seborrheic areas as shown in this photo. Patients do not have mucous membrane involvement. The pathogenic antibodies are anti-desmoglein 1 ...

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