Tzank smear is positive in -

Tzanck smear is a bedside test. It enables cytodiagnosis in vesicular and bullous lesions to demonstrate acantholytic or multinucleated cells. Acantholytic cells are keratinocytes which are large round cells with a dark central nucleus and peripheral condensed pink cytoplasm. These cells may be singular or in groups and are seen in the pemphigus group of disorders. Herpes simplex, herpes zoster and varicella show multinucleated giant cells because of the intercellular septum of the keratinocytes. For the test smear is taken from the floor of the bulla preferably a new lesion and stained with Giemsa or Leishman stain. Smear examined under microscope for the presence of acantholytic cells and multinucleated giant cells indicates positive test Page no.110,Reference IADVL's concise textbook of dermatology