<prompt> A 40-yr-old male repoed with recurrent episodes of oral ulcers, large areas of denuded skin and flaccid vesiculobullous eruptions. Which of the following would be the bedside investigation helpful in establishing the diagnosis?Gram staining of the blister fluidCulture and sensitivitySkin biopsy and immunofluroscenceTzank smear from the floor of bulla  <response>: The given patient has pemphigus vulgaris. The Tzanck testTzanck Smear, is scraping of an ulcer base to look for Tzanck cells. It ia a simple test which can be done bedside in a patient of pemphigus. It shows numerous acantholytic keratinocytes. - rounded and more or less uniform in size, with a relatively large nuclear : cytoplasmic ratio with a perinuclear pale halo, with the peripheral pa of the cell staining more darkly. Skin biopsy and immunofluroscence is more conclusive but is a laboratory test. 