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(a) What is the most likely diagnosis?
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Bullous pemphigoid. The tense blisters, history of itching and the patient’s age makes this the most likely diagnosis.
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(b) Where else would you examine this patient?
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Involvement of mucosal surfaces such as the oral mucosa, genitalia, conjunctiva for blisters and/or erosions.
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(c) What is the underlying aetiology of this condition?
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Development of IgG auto-antibodies to skin basement membrane antigens BP180 or BP230 resulting in cleavage of the skin at the dermo-epidermal junction leading to subepidermal blisters.
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(d) What specific investigations would you undertake in this patient?
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Blood test for serum pemphigoid antibodies.
Skin biopsies: (a) from lesional skin for histology with haematoxylin and eosinophil staining which will demonstrate subepidermal blisters; and (b) peri-lesional skin for direct immunofluorescence which will demonstrate linear IgG at the basement membrane.
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(e) What is your differential diagnosis of a blistering rash?
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Insect bites, drug-induced, infection (e.g. bullous impetigo), other autoimmune blistering diseases (e.g. dermatitis herpetiformis, pemphigus vulgaris).
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(f) How would you treat this patient?
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Given the widespread nature of this patient’s bullous pemphigoid, he should be treated with a reducing course of oral prednisolone starting at about 30 mg/day in combination with an oral immunosuppressant such as azathioprine or mycophenolate mofetil. If he had more limited disease, a trial of topical super-potent corticosteroid such as 0.05% clobetasol proprionate could be tried prior to considering systemic treatment.
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(g) What precautions need to be taken with regards to the use of systemic treatment in this patient?
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As this patient may be on a long period of high-dose oral steroids, he requires osteoporosis prophylaxis and monitoring for steroid-induced hypertension and diabetes. In addition, use of oral immunosuppressants such as azathioprine or mycophenolate mofetil requires regular monitoring of his blood count, renal and liver function.
