An 82-year-old man presents with a 1 and a half-week history of severe pruritus and eczema. His past medical history includes atopic dermatitis, thyroid disease, and multiple sclerosis. On physical examination, he has dozens of 1-2 cm tense bullae and several erosions over his upper and lower extremities. His oral mucosa is not involved. Nikolsky sign is negative. A skin biopsy is taken and anti-BP 180 is detected in his blood. A potent topical steroid is prescribed. The most likely diagnosis is

Ans. is 'b' Bullous Pemphigoid Pemphigoid is commonly seen in old age (60-80 yrs) as bullous eruptions on lower limb. Both pemphigus and pemphigoid give bullous lesions but they differ in other characteristic. Pemphigus Pemphigoid Nikolsky sign present* Bullae are intraepidermal & flaccid* Mucosa involved* Acantholysis present* Involves upper part of body Age of involvement 40-60 yrs* Prognosis poor Nikolsky sign absent Bullae are supepidermal & tense Mucosa not involved Acantholysis absent Involved lower part of body. Age of involvement 60-80 yrs* Prognosis Good