Pemphigus vulgaris:

Pemphigus vulgaris is a potentially fatal blistering disease occurring in all races but commoner in Ashkenazi Jews and possibly in people from the Indian subcontinent. Onset is usually in middle age and both sexes are affected equally. Prior to the development of oral steroids this condition was frequently fatal. The development of autoantibodies against the desmosomal protein, desmoglein 3, is pathogenic in this disease and they can be measured experimentally as markers of disease activity. Rarely the disease can be drug induced (e.g. penicillamine or captopril).
Skin biopsy shows a superficial intraepidermal split just above the basal layer with acantholysis (separation of individual cells). In the rarer variant, pemphigus foliaceous (characterized by anti-desmoglein 1 autoantibodies), the split is higher in the upper epidermis. Both direct IMF of skin (perilesional) and indirect IMF using patients' serum show intercellular staining of IgG within the epidermis.
Clinical features
Mucosal involvement (especially oral ulceration) is common and is the presenting sign in up to 50% of cases. This is followed by the appearance of flaccid blisters, particularly involving the trunk. They tend to be sore rather than itchy. Blistering usually becomes widespread but they rapidly denude; thus pemphigus often presents with erythematous, weeping erosions. Blisters can be extended with gentle sliding pressure (Nikolsky's sign). Flexural lesions often have a vegetative appearance. In pemphigus foliaceous the blisters and erosions often start in a seborrhoeic distribution (scalp, face and upper chest) before becoming more widespread.
Treatment
This is with very high-dose oral prednisolone (60-100 mg daily) or pulsed methylprednisolone, and this may need to be lifelong. Other immunosuppressants such as azathioprine, or mycophenolate mofetil (or occasionally cyclophosphamide or ciclosporin) are used as steroid-sparing agents but they often take many weeks to be effective. Intravenous immunoglobulin infusions may help gain quick control whilst waiting for these other drugs to work. Anti-CD20 monoclonal antibody (rituximab) has recently been reported to help multidrug-resistant cases.
Whilst treatment is normally effective, perhaps up to 10% of patients may die, either because of complications of the disease or more commonly from side-effects of the treatment.
Use of azathioprine.
Azathioprine can cause bone marrow suppression and an allergic hepatitis. Therefore blood count and liver function tests should be regularly monitored during therapy (every 6 weeks). Long-term use with other immunosuppressants causes a slightly increased risk of malignancy, especially of the skin.