Psoriasis, a long standing disease in the history of medicine, has been viewed upon rather differently throughout the ages; considered a curse in the ancient times, a stigmata upon people, and later on during medieval times evaluated as a clinical variety of leper, nowadays we see psoriasis as an apart clinical entity, part of a wider class of diseases called eczemas. The term psoriasis is derived from the greek "psora" which means "to itch".
Eczemas represent inflammation of the skin, also called dermatitis, the subsequent causes of this certain process being extremely various. Classification of eczemas in general, and in the particular case of psoriatic eczema the subclassification criteria are very extensive. However, intuitively all eczemas can be divided into two main groups: exudative eczemas (also called wet-eczemas, because of the reactive local production of different biological secretions) and non-exudative eczemas (also called dry-eczemas, because of the lack of the aforementioned mechanism); psoriasis in particular is a type of dry eczema.
The main difference between usual eczemas (like for example contact-dermatitis, a very common type of eczema that occurs due to an allergic reaction of an individual to a certain chemical) is that of its topographic disposition throughout the body. If all common eczemas tend to be located on flexor sides of the limbs and body (that is, on the same part with the cutaneous folds - between thigh and groin, axillar fold, the fold between the arm and the forearm and so on), psoriatic eczema, in almost all cases is located on extensor sides of the limbs and body. Typical locations for developing psoriasis include the external part of the forearms and arms, the elbows, the back of the torso, knees and the vicinity of the knees.
With still many things not fully understood, and others not at all understood about psoriasis, some facts we do know. Psoriasis is a chronic disease, with an etiology thought to be autoimmune, though proof is not completely conclusive as that to be the only lead. Second on all, the evolution of the disease is chronic, the disease having active and less active periods during its evolution throughout the lifespan of the patient. Since the infectious origin of psoriasis has long been excluded, it is not by any chance contagious. The onset of the disease is variable in time, but it mostly bursts somewhere during the second, third or fourth decade of life; the existence of certain triggers that exacerbate the evolution and symptoms of the disease, has led to the conclusion that this peak of incidence is not a random one. Stress, alcohol consumption, smoking, emotional problems, frustration, lithium salts, beta blockers, streptococcal infection and others are associated with either the onset or aggravation of psoriasis, but cannot be viewed as causal factors by themselves. It is nowadays clear that some individuals express a genetic propensity to psoriasis, while others don't. Since few of the ones genetically predisposed eventually experience psoriasis, the role of various environmental factors in triggering the disease is assumed (some of them we have mentioned above). This is further sustained by the observations made on homozygous twins (identical twins) in who the chance of a twin developing psoriasis on condition the other one has it, is 70% no matter the environment, whereas in heterozygous twins the chance falls down to 20%.
Clinically, the majorly affected organ in most cases is the skin. Typical lessions suppose the existence of red, scaly patches of thickened skin, with erythrodermic areas in the vicinity (red skin). These patches often tend to get a flaky aspect, with the excess keratin being formed starting to vanish by exfoliation of the skin. The appearance of the patches, is actually silvery-white because of this excessive formation of keratin from the skin's keratinocytes; the redness is underlying the patch. The thickened skin is also less resistant to trauma, and since it is crusty it can "fracture" producing minor bleedings that also associate a risk of co-infection with various pathogens. Unlike athlete's foot, a type of fungal eczema that arises between toes, and is favored by a humid environment, psoriasis plaques benefit from humidity; moisture helps preserve the integrity of the skin as a barrier thus reducing opportunistic infections due to cracking, and also alleviate the discomfort created by an abnormal skin texture (pain, itching, psychical discomfort).
However not only the skin can be affected within psoriasis. Nails are sometimes affected, since the so-called nail-bed consists of skin underlying the corneous nail. In such a case usually the nail will degenerate, after passing a few stages of dystrophic evolution - process called onycholysis. Joints are also often affected, with the percentage varying from 10 to 15 percent of all psoriasis patients. Joints include finger and toe joints, knees, coxofemurals and sometimes the joints between vertebrae. Since the joint phenomena is acute, and evolves as an inflammatory condition, the term used to describe it is psoriatic arthritis.
Subdivision of psoriasis in smaller clinical entities, comprises two other main groups: non-pustular psoriasis and pustular psoriasis (with tiny vesicles filled with non-pus liquid called pustules). The non-pustular appears much more often and clinical varieties include psoriasis vulgaris (most common form of disease) and psoriatic erythroderma (a form of extreme psoriatic exacerbation occurring mostly after abrupt interruption of a previous treatment that used to partially or totally control the disease - for example prednisone). Pustular forms include generalized pustular psoriasis, pustulosis palmaris et plantaris (pustules located in the palms and feet) and others. Nail psoriasis and arthritic psoriasis can be seen as separate entities, case in which they could be considered non-pustular, tough it is better not to apply the classification to this forms, or they can complicate a pre-existing different form of psoriasis, like for example the most common psoriasis vulgaris.
Diagnosis of psoriasis is mostly clinical, due to the aspect of the plaques; a skin biopsy could be performed in rather inconclusive cases. A clinical maneuver that allows for confirmation is called Auspitz's sign, and it supposes scratching the scaly patch with a harsh object like for example a key. The yielded result is minor dot-bleeding, since forced exfoliation induces a breach in micro-vessels trapped in the epithelium beneath the corneous excessive layer.
The severity of the disease can be assessed in an individual, for either prescribing the most efficient treatment or for evaluating the impact of the disease on his life. Usually this is performed during trials, since the algorithm called PASI is to laborious for clinical practice; it takes into account extensiveness of lesions, their thickness, age, sex, response to previous therapies and others. Prevalence of psoriasis is incredibly high among Caucasian adults, up to between 1.5% and 2.5%, thus rendering it a huge matter of public health. Fortunately, most cases are mild or moderate, with only up to 8% percent of the cases accounting for severe forms of disease.
There are two main theories trying to explain the disease. The first one, called the in-situ theory, states that psoriasis is a primary flaw of the epithelium, in which cells divide too often, and build up epithelium at a higher rate than normal, this being very similar to what happens during a skin cancer, thus the logical conclusion that it might be a pre-cancerous condition of the skin. The second theory, widely accepted today because of the clinical response of the disease to medicine developed according to it, is that psoriasis is a reactive modification of the skin cells' division rate, due to the influences of the immune system upon them.
Treatment of psoriasis comprises a so-called "ladder approach", meaning that, the more severe the clinical disease is, the more aggressive the initial conceived treatment is. Since there is a wide variability in answer of different individuals to the same clinical approach, dermatologist use a trial-and-error algorithm, in order to find the combination of methods that can control the disease in each individual. A mild form of psoriasis is usually initiated on topical treatment. Topical means "locally applied". The locally applied substance can be for example a moisturizer, an oily substance to preserve natural moisture of the skin, sulfurs, coal tar, a corticosteroid ointment and many, many others. In moderate cases, doctors usually prescribe phototherapy, in which radiant light energy is applied to the affected area; it can be combined with sensitizing chemicals called psoralens during exposure session, and with topical treatment in between the sessions. The severe cases are approached systemically, that is by giving drugs either orally or by injection. Given the results, methods can be combined, no given standard being yet able to satisfy all patients. The prolonged use of a certain method, induces a phenomenon of decrease in its efficiency and of possible symptom aggravation, thus doctors sometimes choose to drop that method for some time, so as to let the disease regain sensitivity to it, process called treatment rotation (because they replace it with another method on the period that the first is dropped). Interrupting certain medication abruptly, causes another phenomenon of symptom aggravation called rebound; this is especially true in corticosteroid treatment, which should never be dropped on the spot, but over the time by diminishing dosages.
FOR SPECIFIC INFORMATION ON TREATMENT SEE "Treatments of eczema"