The skin may blister as a result of different causes (Table 17.1). Disruption of the complex skin basement membrane (BM) at different levels leads to the different blistering skin diseases (Figure 17.1).

The most common causes of blistering are insect bites and severe sunburn. Phytophotodermatitis is an uncommon blistering rash caused by a phototoxic reaction following sunlight exposure after contact with plants containing photosensitising chemicals such as psoralen (e.g. giant hogweed, celery, parsnip and rue). Painful and/or itchy urticated plaques or blisters appear within 24 hours of contact in a streaky pattern at the sites of plant contact (Figure 17.2). Management is with potent topical corticosteroids and anti-histamines and avoiding future contact with offending plants.

Autoimmune Bullous Skin Diseases

Autoantibodies against epidermis or BM components lead to activation of an inflammatory cascade with cleavage of the skin at different levels and blistering (Figure 17.1). Diagnosis is made clinically and confirmed by histology (Table 17.2).

Investigations include serum antibodies to target antigen, biopsy lesional skin for haematoxylin and eosinophil staining (differentiates level of skin cleavage causing the blister), peri-lesional skin for direct immunofluorescence (IMF) and serum for indirect IMF.

Immunofluorescence

IMF helps to differentiate between types of bullous diseases.

Direct IMF

A fluorescein-labelled antibody against the suspect disease-causing antibody and/or complement is added to the peri-lesional skin biopsy from the patient. When examined under UV light it demonstrates the deposition pattern of autoantibodies and complement in the skin characteristic of the different bullous skin diseases (Table 17.2).

Indirect IMF

The patient’s serum containing the disease-causing antibodies are added to an animal tissue (e.g. monkey oesophagus), incubated and highlighted under UV light using fluorescein-labelled anti-human antibody.