Psoriasis is probably one of the longest known illnesses of humans and simultaneously one of the most misunderstood. Some scholars believe psoriasis to have been included among the skin conditions called tzaraat in the Bible. In more recent times psoriasis was frequently described as a variety of leprosy. The Greeks used the term lepra (λεπρα) for scaly skin conditions. They used the term psora to describe itchy skin conditions. It became known as Willan’s lepra in the late 18th century when English dermatologists Robert Willan and Thomas Bateman differentiated it from other skin diseases. Leprosy, they said, is distinguished by the regular, circular form of patches, while psoriasis is always irregular. Willan identified two categories: leprosa graecorum and psora leprosa.

While it may have been visually, and later semantically, confused with leprosy, it was not until 1841 that the condition was finally given the name psoriasis by the Viennese dermatologist Ferdinand von Hebra. The name is derived from the Greek word psora which means to itch.

It was during the 20th century that psoriasis was further differentiated into specific types.

The history of psoriasis is littered with treatments of dubious effectiveness and high toxicity. These treatments received brief popularity at particular time periods or within certain geographical regions. The application of cat faeces to red lesions on the skin, for example, was one of the earliest topical treatments employed in ancient Egypt. Onions, sea salt and urine, goose oil and semen, wasp droppings in sycamore milk, and soup made from vipers have all been reported as being ancient treatments.

In the more recent past, Fowler’s solution, which contains a poisonous and carcinogenic arsenic compound, was used by dermatologists as a treatment for psoriasis during the 18th and 19th centuries. Grenz rays (also called ultrasoft X-rays or Bucky rays) was a popular treatment of psoriasis during the middle of the 20th century. This type of therapy was superseded by ultraviolet therapy.

Undecylenic acid was investigated and used for psoriasis some 40 years ago (circa 1950).

All these treatments have fallen out of favour.

Historically, agents used to treat psoriasis were discovered by experimentation or by accident. In contrast, current novel therapeutic agents are designed from a better understanding of the immune processes involved in psoriasis and by the specific targeting of molecular mediators. Examples can be seen in the use of biologics, which target T cells and TNF inhibitors.

It has been suggested that cannabis might treat psoriasis, due to the anti-inflammatory properties of its cannabinoids, and the regulatory effects of THC on the immune system. The adverse effects of cannabis might be overcome by use of more specific cannabinoid receptor medications, to inhibit keratinocyte proliferation.

Future innovation should see the creation of additional drugs that refine the targeting of immune-mediators further.

Research into antisense oligonucleotides carries the potential to provide novel therapeutic strategies for treating psoriasis.

ABT-874 is a human anti-IL-12 monoclonal antibody being developed by Abbott Laboratories in conjunction with Cambridge Antibody Technology for the treatment of multiple autoimmune diseases, including psoriasis. Phase II trials have been completed and showed promising results. Abbott was planning to initiate Phase III trials in 2007.

In 2004, Tas and Avci demonstrated cyclopamine’s clinical potential for the treatment of psoriasis and basal cell carcinoma in two preliminary proof of concept studies. By treating 31 psoriatic lesions in 7 patients, these authors asserted topical cyclopamine was more effective in the clinical and histological clearance of guttate and plaque psoriasis than the topical steroid clobetasol-17 propionate. Furthermore, they demonstrated concurrent application of cylopamine and clobetasol-17 propionate accelerated regression and clearance of selected lesions greater than cyclopamine alone, with clearance times as early as 48 hours. They assert cyclopamine inhibits the abnormal proliferation of epithelial cells, induces terminal differentiation, and is associated with the decreased presence of inflammatory cells, including CD41 lymphocytes.

On 27 August 2006, scientists led by Jeung-Hoon Lee created the synthetic lipids pseudoceramides, which are involved in skin cell growth, and could be used in treating skin diseases such as atopic dermatitis, a form of eczema characterized by red, flaky and very itchy skin; psoriasis, and glucocorticoid-induced epidermal atrophy, in which the skin shrinks due to skin cell loss.

On 17 November 2008, researchers led by Yin-Ku Lin of Chang Gung Memorial Hospital and Chang Gung University in Taoyuan, Taiwan, told Reuters by telephone that Indigo naturalis, a dark blue plant used in traditional Chinese medicine, appears to be effective in treating psoriasis. In the latest issue of Archives of Dermatology, they wrote, “The Indigo naturalis ointment-treated lesions showed an 81 percent improvement, the (nonmedicated) ointment-treated lesions showed a 26 percent improvement.”

Talarozole amplifies the effects of retinoic acid by inhibiting its metabolism. As of February 2009, it is undergoing clinical trials.

Noting that botulinum toxin has been shown to have an effect on inhibiting neurogenic inflammation, and evidence suggesting the role of neurogenic inflammation in the pathogenesis of psoriasis, the University of Minnesota has begun a clinical trial to follow up on the observation that patients treated with botulinum toxin for dystonia had dramatic improvement in psoriasis. See: Use of Botulinum Toxin to Treat Psoriasis.

Sulphur was fashionable as a treatment for psoriasis in the Victorian and Edwardian eras. It has recently regained some credibility as a safe alternative to steroids and coal tar.

You may also be interested in this thread that shows psoriasis images form the 1800s http://psoriasisclub.org/showthread.php?tid=172