The various clinical forms of psoriasis.

Nail psoriasis, as the name suggests, is identified at the level of the nails of the hands and feet. It takes the form of small isolated or multiple holes of about one millimetre in diameter. Psoriatic foci can be located on several parts: on the surface of the nail and under the nail, but they are visible through it. In this second case, when the plaques continue to develop, the skin thickens and the nail is at risk of completely detaching. This form of psoriasis is particularly bothersome in addition to being painful.

Inverted psoriasis is observed on skin folds, particularly the armpits, the intergluteal cleft, the navel, the skin under the breasts, and the skin between the fingers or toes. Unlike plaque psoriasis, which presents with thick plaques, inverted psoriasis is characterised by thin red plaques. Scaling is generally absent or negligible, and the lesions present a bright, clearly defined erythema. This form of psoriasis is more common in individuals affected by obesity. Moreover, it is generally more resistant to conventional treatments.

Guttate psoriasis is a form of psoriasis characterised by thin plaques with minimal scaling, which form on the torso, back, and limbs. It typically occurs in children and young adults. It can occur alone (acute guttate psoriasis) or exacerbate an existing chronic plaque psoriasis, often quite limited (guttate flare-up of chronic plaque psoriasis). These plaques spread rapidly over the entire body when they measure less than one centimetre. The hair and nails are spared in most cases. The droplets formed by guttate psoriasis can cause itching in the patient. After the plaques disappear, the red lesions heal quickly.

The pustular psoriasis is a term referring to a rare form of non-contagious skin psoriasis. Its prevalence is estimated at 2 cases per 1 million people. It is characterised by a sudden and widespread eruption of superficial sterile pustules, which are non-infectious but inflammatory. The lesions are accompanied by pain, a burning sensation or itching in some patients. It happens that the same subject suffers from both pustular psoriasis and plaque psoriasis. In this case, the plaques of the eruption can be scaly and erythematous. Pustular psoriasis presents in two forms:

• Palmoplantar pustulosis (PPP),a term used when the disease lesions are concentrated on the hands or the soles of the feet;

• Generalised pustular psoriasis (GPP), a term used when the disease lesions spread over the entire body.

This type of psoriasis develops on the palm of the hands, as well as the soles of the feet. Particularly dry, its lesions create painful cracks. When they are located on the soles of the feet, they can be debilitating. The scales are the predominant lesions. Thick scales can give the appearance of keratoderma.

This clinical form of psoriasis is characterised by lesions that can affect up to 80% of the body surface. In patients with erythrodermic psoriasis, hypothermia due to generalised vasodilation can be observed. Erythrodermic psoriasis is always accompanied by fever and chills. It is a rare form of psoriasis that is severe and requires prompt treatment.

This form of psoriasis is characterised by well-defined red patches with either dry or oily scales. These can be found on the forehead, nose, or even the chin. These plaques can be painful, uncomfortable, and cause the skin to feel tight. Furthermore, this type of psoriasis is twice as common in children.

Scalp psoriasis is characterised by patches covered with irritating scales present on the scalp. This is the most commonly involved area and many patients discover they have psoriasis due to dandruff-like flaking of the scalp. It is estimated that 50 to 80% of people with psoriasis also have scalp psoriasis.