Diagnosis

Pemphigus can scarcely be confounded with anything else, the bullae are so diagnostic a sign. In eczema of the hands, bullae may be produced secondarily by the confluence of vesicles, but their origin is readily traced, and co-existent eczema is to be found elsewhere. Pemphigus is rare on the hands and fingers, per se. General ecze­ma and P. foliaceus should not be confounded; in the latter abortive bullae are present, the scales are larger and peculiar, and the skin is not infiltrated.

In ecthyma cachecticum the pustules contain bloody fluid; there are no true bullae in the disease; the crusts are also thick and dirty; whilst the ulceration is deep. In rupia, the bullae are smaller and natter, the contents sanious, the crusts thick, dark, prominent - cockleshell like; the ulceration deep and foul. Pemphigus foliaceus resembles pityriasis rubra; but in the latter there is no history of bullae; the scales are altogether smaller, and they are imbricated in a peculiar manner.

Sometimes  in  impetigo contagiosa,  the bullae become somewhat large, but they are never distended as in pemphigus, but flat; the contents soon become purulent, flat yellow scabs form, which are characteristic. The disease is clearly pustular.