From a clinical perspective, psoriasis can be regarded as a spectrum of different skin manifestations. At any one point in time, different variants may coexist in a particular individual, but the skin lesions all share the same important hallmarks: redness, thickening of skin and scales.
During psoriasis flares, skin lesions often itch. If there are smaller, pinpoint-size lesions surrounding a chronic plaque, that indicates a flare or unstable phase of the skin disease. Depending on the clinical appearance, there are five types of psoriasis: inverse, plaque, guttate, erythrodermic and pustular.
Chronic Plaque Disease
The most common type of psoriasis is called psoriasis vulgaris. It is known by its characteristic thick, silver scales. This is a relatively symmetrical, sharply demarcated variant that affects the scalp, elbows, knees and lower back.
Plaques may persist for months to years in the same locations. Although the course of this disease is chronic, periods of complete remission do occur, and remissions of five years or more have been reported in approximately 5 percent of patients.
Guttate, or “gumdrop,” psoriasis represents a form of small, discrete lesions in a diffuse pattern. This variant is rare — seen in approximately 2 percent of all psoriasis patients. However, it is common in children.
It occurs acutely following streptococcal infection and is typically found in patients younger than 30 years old. It typically manifests as a sore throat or less commonly as a red rash around the anus.
The prognosis is excellent in children, with spontaneous cure rates often occurring over the course of weeks to months. It responds well to oral antibiotics to treat the infection as well as sunlight therapy. In contrast, in adults, the lesions of guttate psoriasis can become chronic.
The skin of patients with erythrodermic psoriasis becomes red, scaly and warm, though it often spares the face. Patients may be at risk for cardiac failure because their heart can’t supply enough blood to the skin to maintain its vital functions. This is a medical emergency.
Another severe form of psoriasis is pustular psoriasis, which shows up as pus around the nails, palms of the hands, soles of the feet and at the edge of existing psoriatic plaques. Patients can become extremely ill with this subtype, having fever, generalized redness, low blood calcium and poor appetite.
The scalp is one of the most common sites for psoriasis. The individual lesions are often discrete. This form of psoriasis often coexists with seborrheic dermatitis, which is often milder and less discrete. The lesions of psoriasis may cause hair loss due to the thick scales.
Inverse psoriasis occurs within skin folds and on surfaces like the ears, underarms, groin, navel, intergluteal crease, genitals, lips and beneath breasts. The genitals are involved in up to 30 percent of patients.
With this type of psoriasis, the tongue may become fissured and ridged. Smooth, red patches on the tongue (also called geographic tongue) are common in patients suffering from psoriasis, especially during a flare. This form presents as migrating, ring-like white plaques on the tongue.
Nails are commonly affected by psoriasis and may split or separate from the nail bed. Pitting of the nails like hammered brass, yellow oil spots and thickening of the nail with debris under the nail plate(similar to nail fungus, or onychomycosis) may occur in patients with psoriasis.
Psoriatic arthritis occurs in 5 to 30 percent of patients with skin psoriasis. In a small percentage of patients, the symptoms of the arthritis may appear before the involvement of the skin. Psoriatic arthritis may also resemble rheumatoid arthritis.
Early diagnosis is essential to avoid joint deformity. An important hallmark of psoriatic arthritis is erosive change, which may occur years after the presenting inflammation of the joints. It often affects the hands and can give the characteristic “sausage digit” deformity from the inflammation of the joints of the fingers.