What is IgA pemphigus?
IgA pemphigus (or immunoglobulin A pemphigus) is an autoimmune blistering disorder. It is also called intercellular IgA dermatosis among other names.
IgA pemphigus has two major subtypes:
- Subcorneal pustular dermatosis (SPD) type
- Deposition of intracellular IgA against the glycoprotein desmocollin-1 seen predominantly in the upper epidermis.
- Intraepidermal neutrophilic (IEN) type.
- Deposition of autoantibodies against desmoglein members of the cadherin superfamily seen predominantly in lower epidermis.
However, a new classification describes five subtypes of IgA pemphigus; these being:
- SPD type IgA pemphigus
- IEN type IgA pemphigus
- IgA-pemphigus vegetans
- IgA-pemphigus vulgaris
- Unclassified IgA pemphigus.
It has been associated with malignancies (multiple myeloma) and several chronic conditions (monoclonal IgA gammopathy, human immunodeficiency virus infection, Sjögren's syndrome, rheumatoid arthritis, and Crohn's disease).
Who gets IgA pemphigus?
IgA pemphigus is very rare. It can occur in any age group, but is more commonly seen in middle aged adults and may have a female predominance.
What are the clinical features of IgA pemphigus?
The clinical features of IgA pemphigus include blisters, pustules, erythema, erosions and vegetating lesions.
- The first signs are flaccid vesicles and pustules.
- The vesicles and pustules rupture to form erosions and crusted plaques.
- The eruption tends to follow an annular pattern.
IgA pemphigus appears to favour the trunk, upper and lower extremities, axillae, and groin. Mucosal involvement is infrequent.
What is the cause of IgA pemphigus?
The exact cause of IgA pemphigus is unclear.
- IgA autoantibodies bind to desmogleins or desmocollins, the cells responsible for adhesion between cells.
- In SPD-type IgA pemphigus, the autoantigen is described as desmocollin 1, one of the desmosomal cadherins, the glycoproteins that maintain the shape of a cell.
- In at least some cases of IEN-type IgA pemphigus, the autoantigens are desmoglein 1, desmoglein 3, and an unspecified transmembrane protein.
What is the differential diagnosis for IgA pemphigus?
Other conditions that should be considered in the differential diagnosis include:
- Bacterial skin infection
- Dermatitis herpetiformis
- Pemphigus foliaceus
- Eosinophilic pustular folliculitis
- Subcorneal pustular dermatosis / Sneddon-Wilkinson disease.
How is IgA pemphigus diagnosed?
A blistering autoimmune disease or autoinflammatory pustular disease may be suspected clinically from the clinical features, often after the eruption has failed to clear with antibiotics.
The diagnosis of IgA pemphigus requires a skin biopsy for histology and direct immunofluorescent testing.
- In IgA pemphigus, a skin biopsy reveals intraepidermal neutrophil infiltration. Blistering skin specimens will show mixed inflammatory infiltrate in upper, mid or lower epidermis, depending on the subtype with little or no acantholysis.
- Direct immunofluorescence of a skin biopsy of healthy appearing skin close to the area of blistering reveals IgA deposition in epidermal keratinocyte cell membranes.
Indirect immunofluorescence testing of serum can show IgA anti-keratinocyte cell-surface antibodies. Immunoglobulin G (IgG) anti-keratinocyte cell-surface antibodies have also been reported.
What is the treatment for IgA pemphigus?
IgA pemphigus is usually treated with a combination of systemic steroids (anti-inflammatory effects) and dapsone which is thought to reduce neutrophil infiltration. This combination treatment is more effective than the use of steroids alone.
Since few cases of IgA pemphigus have been described, the most effective treatment is unknown. Other medications worth considering include:
In comparison to other forms of pemphigus, IgA pemphigus presents with a milder disease and carries a better prognosis. When managed appropriately, it mostly heals with no scarring.
Patients should be counselled about potential side effects of steroids and dapsone. IgA associated with other medical conditions should be managed in a multidisciplinary manner, hence it is important to thoroughly investigate potential underlying triggers/associations, especially in elderly patients.