Types of psoriasis
You may find that your psoriasis comes and goes and disappears for months or years at a time. You may even have only one episode during your lifetime. The condition may start slowly, with just a few patches, or much more explosively, especially after a sore throat caused by the bacterium Streptococcus.
Psoriasis is usually easy for doctors to diagnose. However, it can be mistaken for other skin conditions. In elderly people, for example, psoriasis can be confused with eczema. Eczema and psoriasis are both common disorders, and you may even suffer from the two conditions at the same time.
ECZEMA VERSUS PSORIASIS
Eczema is also known as dermatitis and typically causes a dry, irritated skin. It exists in a variety of forms, including an inherited tendency to a group of allergic conditions such as atopic eczema, asthma and hayfever and irritation or allergy of the skin after exposure to certain chemicals (contact dermatitis).
The word eczema literally means ‘to boil’. In the initial stages of the condition, your skin can look as if it has been boiled, with a red appearance and tiny blisters. This is usually followed by dryness and scaling – it is at this stage that eczema can be mistaken for psoriasis.
Elderly people are prone to dry skin and eczema and it is often difficult to decide whether their rash is the result of eczema or psoriasis or both – even a biopsy may not be conclusive. It is important to discover the cause of the rash, because some of the topical treatments for psoriasis can irritate skin affected by eczema.
In young adults, it can be difficult to distinguish between psoriasis and seborrhoeic dermatitis. Seborrhoeic dermatitis is a form of eczema that produces a scaly scalp and characteristic rash on the face and trunk. It is caused at least in part by an infection with a yeast called Pityrosporum. Seborrhoeic dermatitis typically affects the front of the scalp, eyebrows, outer part of the ears, the sides of the nose, laughter lines around the mouth, and under the arms, breast and groin. It also causes irritation of the eyes.
Psoriasis may be confused with seborrhoeic dermatitis because psoriasis can affect the same areas of the body in its initial stages. The treatments for the conditions are different, so it is important to try to differentiate between the two, although sometimes only time will tell. The treatment for seborrhoeic dermatitis involves anti-fungal creams and hair preparations (Nizoral) and creams containing sulphur and salicylic acid to help dampen down the inflammation. Seborrhoeic dermatitis, like psoriasis, can’t be cured, but can be greatly improved.
PLAQUE PSORIASIS
This is the most common form of psoriasis. The individual plaques are not usually very itchy. They are, however, red and covered with flaky silvery-white scales. If you scrape away the scales, with a fingernail, for example, the plaques may bleed.
The plaques usually have a clear edge, unlike most forms of eczema, and are usually symmetrical (one side of the body mirrors the other). The most common affected sites are the elbows, knees and scalp, but the plaques can occur anywhere on your body. Fortunately, the face is not commonly affected, although your forehead may be if your scalp is involved, with plaques appearing in front of your hairline.
The appearance of the plaques depends on where they are found on your body. In moist areas, such as the creases of the armpits and the groin, between the buttocks and under the breasts, there is little or no scaling – the patches are red with a sharp border. The palms and soles, however, tend to be scaly, but, because the skin is much thicker at these sites, the colour of the plaques is much less red. In most people, the plaques are large, often several centimetres or more across. Occasionally, people have several much smaller lesions of up to one centimetre.
GUTTATE PSORIASIS
Guttate psoriasis usually occurs in children or young adults, and often follows a severe sore throat or bout of tonsillitis caused by a streptococcal infection. The sore throat is followed 7 to 14 days later by the sudden appearance of plaques of psoriasis all over the body, especially on the trunk and limbs. The plaques are small, usually less than one centimetre in diameter. Itching is usually mild or absent. This type of psoriasis has an excellent outlook, and usually settles within a few weeks or months with topical treatments. A short course of ultraviolet light is also helpful.
PUSTULAR PSORIASIS
Pustular psoriasis usually exists as a large red area covered with green tender pustules (blisters) that are two to four millimetres in diameter. Despite their colour, the pustules are not infected. The green colour is caused by masses of white blood cells called polymorph leucocytes. These cells flood into any part of the skin that is inflamed or damaged. After 7 to 10 days, the pustules become dispersed and a brown scale appears. This brown scale is shed as further pustules develop elsewhere, often in a continuous cycle.
In the most common form of pustular psoriasis, the palms and soles are involved. Unlike eczema covering these areas, the psoriasis tends to be sore rather than itchy. Pustular psoriasis is uncomfortable and unsightly, and can make writing or walking difficult.
A less common form of pustular psoriasis occurs when ordinary plaques of psoriasis start to blister. This can happen spontaneously, but is more likely to follow the long-term use of strong topical corticosteroid treatments.
The most severe – and fortunately the most rare – form is called generalised pustular psoriasis. A patient becomes ill and feverish, and there is a sudden onset of tiny pustules all over the skin, usually starting on the upper trunk but spreading all over within hours or days. This requires hospital admission. Generalised pustular psoriasis can occur in people who already have psoriasis, but it sometimes occurs in people without this medical history. Occasionally, the pustular change is induced by the overuse of strong topical corticosteroid applications.
ERYTHRODERMA
This is fortunately a rare event, but can be serious and even life threatening in elderly people. It can even occur in someone without a history of psoriasis. In people with erythroderma, their skin becomes red and hot and continually scales. They lose their ability to control their body temperature and lose heat, body fluids and protein. Inpatient treatment may be required and involves supportive measures, such as intravenous drip to replace the lost body fluids and applying soothing products and weak steroid creams. Full recovery is possible, although the outlook depends on the severity of the condition, overall health of the person affected and speed of treatment.
NAPKIN PSORIASIS
Psoriasis in babies is rare. Most rashes that occur in the nappy area are caused by eczema, a fungus called Candida (thrush) or the irritant effect of urine. However, occasionally a red rash with a sharp border occurs and looks like psoriasis. Some babies can develop plaque psoriasis on their elbows and knees. Nappy rash is initially treated with an anti-fungal cream (Canesten) or an anti-fungal and steroid combination (Canesten-HC). The likelihood of the baby developing psoriasis later in life is increased, although not inevitable, and needs to be discussed with a specialist.
LINEAR PSORIASIS
Most psoriasis is symmetrical and widespread. But very occasionally, someone with psoriasis has only the red patches and white scaling in a line down one limb or possibly on the trunk. This linear or naevoid type of psoriasis needs to be distinguished from other linear rashes, such as an epidermal naevus (birthmark) or an unusual form of eczema. A biopsy will usually show the typical changes of psoriasis under the microscope. The treatment and outlook are the same as for plaque psoriasis.
PLAQUE PSORIASIS AT DIFFERENT SITES
Scalp
The scalp is a very common site for psoriasis and you may find that it is the only area involved. Usually, psoriasis on the scalp consists of clear-edged patches that are red, scaly and often lumpy. Hair is not usually affected. Scalp psoriasis is quite unlike seborrhoeic dermatitis, which has much more diffuse scaling, no lumpiness and no well-defined patches. Moreover, psoriasis often extends beyond the hairline. Sometimes psoriasis starts off looking like seborrhoeic dermatitis before evolving into more typical psoriasis.
The treatment of scalp psoriasis involves oily preparations with three per cent salicylic acid to reduce scaling (for example, Meted). You rub these preparations into your scalp three times a week, then wash them out with tar shampoo (for example, Clinitar) four to six hours later. You may even find that a combined salicylic acid and tar combination, such as Cocois, is sufficient. Vitamin D derivatives, such as Dovonex, can also be useful. Good short-term results can be obtained by using steroid scalp applications such as Betnovate, but these aren’t as effective in the long term.
Flexures (creases)
You may find that psoriasis occurs where your skin creases, such as in your armpits, under your breasts, in your groin, between your buttocks and on your genitalia. As these sites are very moist, the plaques lose their scales and tend to be red with a sharp border. You may find the psoriasis is sore, especially while you are moving around.
The treatment is a combination of anti-fungal and steroid creams, such as Canesten-HC. The outlook is the same as for plaque psoriasis, although flexure psoriasis may be particularly obstinate to treat because it can be difficult to get creams to stay in place without being rubbed off. In addition, the constant chafing that may occur in the skin creases (under heavy breasts, for example) can make it hard for the skin to recover.
Palms and soles
When plaque psoriasis occurs on the palms and soles, the patches are less red with thicker, more adherent scale than in plaque psoriasis elsewhere on the body, where the scale is much finer and flakes off easily. Sometimes, the skin’s surface is cracked. If your fingertips are involved, it can be quite sore. Treatment is with moisturisers (E45, for example) and steroid creams or vitamin D analogues used topically, but the same problems seen with psoriasis in the flexures can occur and may delay healing.
Mouth
Psoriasis rarely, if ever, involves the mucous membrane (the membrane lining the mouth). However, in severe cases, the tongue can be involved, producing a characteristic pattern called the ‘geographical tongue’. This is usually without symptoms. Geographical tongue often occurs in people who have no skin disease of any kind, but has also been noted in generalised pustular psoriasis.
Köbner plaque psoriasis
Sometimes psoriasis occurs in injured skin, most commonly appearing as a line in an operation scar or in scratches. Occasionally, it develops in the spots produced by chickenpox. Some other skin diseases can also be triggered in this way, but this is particularly common with psoriasis. Once triggered, the rash looks the same as before, but stays in lines, although the plaques may enlarge and look typical of plaque psoriasis, especially after chickenpox. The phenomenon of Köbner psoriasis may be associated with more conventional psoriasis at the usual sites.
Nails
The fingernails and toenails are commonly affected by psoriasis. The nails may be pitted or start to separate from the nail bed (a process called onycholysis). In onycholysis, the nail usually has a whitish appearance. It is possible to get either pitting or onycholysis without necessarily having psoriasis, but if you get both nail problems together, psoriasis is likely to be the cause. If the nail is severely damaged, it will become crumbly. It is important to exclude tinea (ringworm) as a cause by taking nail samples.
If you have psoriasis of the nails, you may notice that your nails grow more quickly than normal. Although the treatment of this form of psoriasis is extremely difficult, good nail care by a professional manicurist may help to disguise the appearance of your nails.