Pemphigus foliaceus
Overview
The pemphigus family are rare autoimmune blistering diseases affecting skin and/or mucous membranes. Pemphigus foliaceus (PF) is a rare relatively benign form of pemphigus. In New Zealand pemphigus foliaceus is more often encountered than its more serious relative pemphigus vulgaris, although worldwide pemphigus vulgaris is more common. Pemphigus foliaceus is characterised by blistering lesions on otherwise healthy-looking skin. Blisters tend to form when the skin is rubbed (Nikolsky sign). There are currently 6 subtypes: * Pemphigus erythematosus * Pemphigus herpetiformis * Endemic PF * IgA PF * Paraneoplastic PF * Drug-induced PF.
Symptoms
Pemphigus foliaceus is confined to the skin and there is little or no involvement of mucous membranes. This is in contrast to pemphigus vulgaris where there may be extensive mucous membrane involvement (mouth, eyelids etc). The patient is usually otherwise in good health. Small fluid-filled blisters first form on the trunk. Because they form in the upper layers of the epidermis they rupture very easily and only erosions may be seen. On the face, scalp and upper trunk the lesions are often scaly and crusty on a red and inflamed base. A burning sensation or localised pain may be felt. Pemphigus erythematosus is a variant that just affects the face and overlaps with lupus erythematosus.
Causes
Pemphigus foliaceus is an autoimmune disease, which basically means that an individual's immune systems starts reacting against his or her own tissue. The building block cells of the epidermis are called keratinocytes. These cells are cemented together at special sticky spots called desmosomes. In pemphigus foliaceus autoantibodies bind to a protein called desmoglein-1, which is found in desmosomes in the keratinocytes near the top of the epidermis. The result is the surface keratinocytes separate from each other, and are replaced by fluid: the blister. Because the blister is very close to the surface of the skin the blisters rupture easily. In most cases the autoantibodies are immunoglobulin type G (IgG) but in IgA PF the autoantibodies are type A (IgA). PF is sometimes provoked by sun exposure. Endemic PF occurs in South America, where it is commonly known as Fogo Selvagem. It appears to be set off by a virus transmitted by an insect bite. Penicillamine, nifedipine, captopril or nonsteroidal anti-inflammatory drugs most often provoke drug-induced PF. If the drug is stopped, there is a 50% chance the PF will clear up.
Diagnosis
Diagnosis generally requires a skin biopsy, which shows typical features of rounded-up separated keratinocytes (called acantholytic cells) within the blisters in the upper layers of the epidermis. PF is confirmed by direct immunofluorescence staining of the skin sections to reveal antibodies. In some cases, circulating antibodies can be detected by a blood test (indirect immunofluorescence test).
Treatment
Spontaneous remission may occur in some patients whilst in others the problem may persist for several years. The primary aim of treatment is to prevent new areas from developing infections and promote healing of affected areas. Topical treatment with corticosteroids and antibiotics is usually all that is necessary for mild cases of pemphigus foliaceus. For more severe cases treatment is similar to that for pemphigus vulgaris.