Pemphigus is a group of immunologically mediated skin diseases.

Pemphigus means blister. Pemphigus is a term reserved for auto-antibody diseases where the antibody is against structures intra-epidermal (as opposed to sub-epidermal in bullous pemphigoid). Read differences between pemphigus vulgaris and bullous pemphigoid.

This loss of cohesion between epidermal cell is called acantholysis. "Acantho-" means spinous or thorny. Remember the spinous layer of epidermis?

Pemphigus Vulgaris

PV is life threatening because a lot of epithelium is lost (just like in burns). Around 5% mortality.

Antibodies are against desmoglein 1 and 3 in desmosomes (macula adherens). This leaves the blister very flaccid and easily breaking leading to the following signs

Nikolsky sign

The blister breaks when you just touch it. In fact, it is difficult to find an intact blister.
YouTube video

Asboe-Hansen sign

Fancy way to say indirect Nikolsky sign or Nikolsky sign II. Blisters grow in size by extending to unblistered skin when pressure is put. Negative in the above video.

Manage PV

By steroids along with steroid sparing drugs (immunosuppressants)