It is a chronic constitutional disease, which is characterised by cutaneous lesions of the squamous type on the skin with itching as main complaint with silvery scaly plaques or eruptions and may bleed as a droplet on scratching . It normally appears in the early years of the childhood, or at almost any later period upto middle age. It is rarely seen to occur during infancy and old age. Psoriasis occurs throughout the globe; in the temperate zones. Nearly 2% of the population is affected .
     There is no specific cause known for this disease. Aetiological factors can be Genetic factors; Infection ; Emotional trauma ; Mechanical trauma and Drugs.It may be seen in the form of extensive eruptions on the skin of the individuals who otherwise enjoy the most robust health in general , and on the contrary it may appear only during periods of temporarily debility, as in women during pregnancy and lactation. It is considered to be a constitutional affection and connected with similar conditions to those underlying Eczema. It is believed by some that the eruptions are purely local or are due to the presence of some parasite. Though no conclusive evidence is available. The another school of thought say that it is but a relic of Syphilis handed down from a remote ancestor. This view also has little to support it.
     Certainly Psoriasis is often seen as Hereditary. Males are more affected than the Females and it is common between the age of 15 to 30 years of life. It is widely seen that the persons of sanguineous temperament are most liable to the disease and no class of society is particular to be affected and it is also seen both in winters and summers.
Psoriasis has tendency to recur and it is one of the difficult disease to be cured. The most obstinate cases are those of Psoriasis Mumularis of the back and buttocks, in which there is much elevation and thickening and deep redness, and psoriasis about the hands and feet.
     First manifestation of the psoriasis is usually as small red papules, soon decked with a white scale. They may appear as few and scattered, or many and closely aggregated. The scaly papules increase at their periphery, becoming flattened patches from the size of a pea to that of a coin or even larger. When the progress of the disease continues, neighbouring patches encrach on each other, and in time coalasce, giving rise to irregular gyrate forms. Coincident with the peripheral extension there is an increase in the infiltration or thickening of the skin, and the scales become large, imbricated , and more or less adherent. On forcible removal of the scales, a red infiltrated patch is brought to light, on the surface of which minute droplets of blood may be seen. Greater portion of the surface ,may undergo a gradual involution and disappear on the attainment of the disease to its maximum development .Usually clinical features are Plaque psoriasis; Flexural psoriasis ; Pustular psoriasis and Nail involvement. In almost every instance the eruption reappears after a shorter interval . Recurrence of the skin lesions at the beginning of the cold and a disappearance of them at the beginning of the warm seasons. Relapsing feature of the disease is one of the most important and most annoying characteristics hence there is no certainty of a radical cure. It is believed that if a person once has psoriasis , he may expect to have it always, that is, with certain intervals of freedom.
Symptoms Of Psoriasis
     The subjective symptoms are usually unimportant, amounting at most to a moderate degree of itching or pruritus, though in many cases this is not sufficient to be complained of by the patient. Usually eruptions show more or less symmetrical dispositions and generally occur on the extensor surface, with a special regional affinity for the Elbows and Knees. The upper half of the body is more affected than the lower. Rarely it affects the soles and palms.
     The features of the disease are the more characteristic if account be taken of its negative signs , for in it there is an entire absence of any discharge, vesiculation, or pustulation throughout the whole course of disease. The characteristics described constitute primary condition.
     Because of the thick epithelium especially of the elbow and knees the eruptions of psoriasis affects here more. It may be partial or general . At the outset the disease may be attended by more or less pruritus. Usually the psoriatic patches increase by centrifugal growth and show slightly red margins, the scales are shed, to be again replaced by the others. In the chronic cases the derma itself becomes very distinctly infiltrated and thickened. The general health is often apparently good. Fortunately the disease is non - contagious, though runs a chronic course, and is very prone to recurrence. It is essential to learn to distinguish Psoriasis from Syphilis, Eczema and Exfoliative Dermatitis or Dermatitis Exfoliativa . A squams cell syphilide may closely resemble psoriasis; but here the history will reflect by keeping the fundamental facts in mind. In the case of psoriasis patient the history of repeated outbreaks of same kind of eruptions would be the determining factor for the diagnosis. As syphilis rarely repeats itself in its manifestations, in addition there could be other coexisting lesions , as alopecia, mucuous patches, throat trouble etc. In psoriasis the epidermic proliferation or desquamation is much greater than in syphilis. Chances of mistake are there in a case of Exfoliative Dermatitis to be thought as of psoriasis. Though Psoriasis and Syphilis may of course coexist. Psoriasis may coexist with eczema ,bot presenting typical lesions, or may have lesions of mixed character. There it becomes very difficult to say that which disease is predominated. Certain diseases of other organs appear to bear a close relationship to psoriasis and the commonest are the Arthritis and Asthma. As a rule , these do not coexist with the psoriasis, but manifest during the time that the skin is free from eruptions, alternating as it were with the cutaneous lesions.