Chapter 22: Immunobullous Diseases

INTRODUCTION TO CHAPTER

The immunobullous diseases are uncommon chronic skin disorders caused by autoantibodies directed against various cutaneous proteins. These disorders primarily occur in older adults and can cause significant discomfort in affected patients and can even be fatal in the case of pemphigus. Patients with immunobullous diseases often have significant quality of life issues in questions pertaining to physical, emotional, and mental health.¹ Skin biopsies for routine histology and immunofluorescence are needed to confirm the diagnosis.

BULLOUS PEMPHIGOID

Introduction

Bullous pemphigoid is an uncommon blistering eruption that primary affects elderly patients. The mean age of onset ranges from 68 to 82 years of age.

The incidence is estimated to be between 4.5 and 14 new cases per million per year. It is more common in women.²

Pathophysiology

Bullous pemphigoid is an autoimmune disease associated with the production of autoantibodies targeting the basement membrane. The basement membrane is important for the adhesion of the epidermis to the dermis, and so when targeted, leads to a separation (blister) in this space. The antigens themselves are parts of the hemidesmosomes of the basal cells. The targets are BP 180 and BP 230.³ BP 180 is a transmembrane protein in basal cells, which is the extracellular noncollagenous domain of type 17 collagen. BP 230 is a cytoplasmic plakin family protein of the hemidesmosome. There is evidence for the pathogenic roles of these autoantibodies in this disease, especially against BP 180.

Clinical Presentation

History

Despite being labeled a blistering disorder, many patients will present initially with prebullous pemphigoid which presents as a pruritic urticarial rash without blisters.^4,5 The pruritus can be severe. When blisters develop, they are tense blisters because they are forming between the dermis and epidermis and do not easily rupture.

Physical Examination

In the prebullous phase, the patient has pruritic urticarial plaques. In the bullous phase, the patient develops blisters. Most commonly the tense blisters are bilateral, symmetric, and on the trunk and proximal flexural extremities (Figure 22-1). The blisters may or may not have surrounding erythema. Mucosa can be involved, but usually in less than 20% of patients.

Laboratory Findings

• Histopathology of a skin biopsy from the edge of an intact bulla shows a subepidermal bulla with a dermal eosinophil inflammatory component (Figure 22-2).

• Direct immunofluorescence of a skin biopsy taken of normal skin near a bulla shows a linear deposition of C3 and IgG along the basement membrane zone (Figure 22-3).

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