Psoriasis--100 years ago. 
Psoriasis appears to be a very old disease.  Notwithstanding that, it has been described as a clinical entity only in the early 19th century.  By the end of that century, psoriasis comprised a spectrum of clinical variants which have remained almost unchanged since.  And despite a wealth of new information on this disease, both etiology and pathogenesis are still elusive and a matter of discussion and controversy in our days.  A perspective as to the state of the art 100 years ago is presented.