Psoriasis – overview

What is psoriasis?

Psoriasis is a persistent, scaly skin disease. It causes red patches on the skin with thick, firmly attached scales. The condition is caused by a disturbance in the growth of skin cells. Psoriasis is very common: about 2% of the population has it.

How does psoriasis develop?

Normally the skin renews itself gradually: old skin cells are shed from the surface while new ones grow at the base of the epidermis. In psoriasis, the production of skin cells is accelerated and the excess cell layers are not shed. This creates plaques of skin with a thick layer of immature skin cells that scale off only with difficulty. The cause of this disturbed skin production is genetic.

Who develops psoriasis?

Psoriasis occurs at all ages. It usually begins after puberty, but babies and older people can also develop it. There is a clear familial component: the children of a person with psoriasis have about a 10% chance of developing it themselves. Some medicines can trigger or worsen psoriasis; examples are beta-blockers and lithium. Smoking is also a significant risk factor: smokers have up to a threefold greater chance of developing psoriasis than non-smokers, and stopping smoking can improve the complaints in many patients.

Which forms of psoriasis are there?

Psoriasis vulgaris — very typical are red, scaly patches on the extensor sides of the arms and legs, particularly the knees and elbows. This is the most common form, which is why it is called psoriasis vulgaris (“ordinary” psoriasis).
Guttate psoriasis — also common, characterised by many small, scaly pink-red spots spread over the body.
Inverse psoriasis — unlike ordinary psoriasis, the lesions appear in the skin folds, such as the groin, armpits and, in women, under the breasts. Inverse psoriasis is usually not scaly: the patches are pink-red and shiny and usually not thickened.
Scalp psoriasis (psoriasis capitis) — psoriasis on the hairy scalp can sometimes resemble “dandruff” (seborrhoeic eczema).
Nail psoriasis (psoriasis unguum) — the nails are often involved. Characteristic are small pits in the nail plate. In more severe forms a layer of hard skin also forms under the nail, lifting the nail plate.
Psoriatic arthritis (psoriasis arthropathica) — with all the forms described above, painful joints can also develop.
Palmoplantar pustular psoriasis — in this special form there are small, pus-filled blisters on the palms and/or soles. It is seen almost exclusively in smokers.

What is the course of psoriasis?

The features of psoriasis are very unpredictable. The patches can remain limited to a small area of skin for a long time. Yet a sudden, major flare can occur — for example after a (throat) infection or the use of certain medicines. Stress can also be an important reason for psoriasis to spread. In many cases a worsening cannot be well explained. Fortunately, psoriasis can settle into calmer waters again, even after a prolonged flare.

The impact of psoriasis on daily life

Psoriasis is a very visible condition. Even when the number of patches is limited, there can be a major impact on a patient’s social life and self-confidence. Some patients are relatively untroubled by their skin disease and what others may think of it, but a much larger group struggles with feelings of shame. People with psoriasis sometimes avoid activities where they have to expose part of their skin, such as swimming, and on holiday may try to wear covering clothing even in warm weather so as not to show their skin condition. Starting intimate relationships can also be harder, as insecurity and shame about one’s own body can form a significant barrier.

Experience shows that sharing experiences with other people who have psoriasis (for example through a patient association) is of great value in coping. Informing friends, family and colleagues is also important — not only to educate those around you (“No, it is not contagious…”) but also to reduce your own feelings of shame and increase your self-confidence.

Psoriasis and the heart

In recent years it has become clear that having psoriasis also increases the risk of developing cardiovascular disease. It is therefore extra important for people with psoriasis to adopt a healthy lifestyle: eating healthily, not smoking and exercising sensibly all help reduce the risk of heart and vascular disease.

The burden of treatment

Beyond the social impact, there is also the (usually daily) treatment routine: the many tubes on the bathroom shelf, applying the often greasy ointment every day, pyjamas sticking to the skin. In severe forms, ointment therapy sometimes has to be supplemented with taking or injecting medicines on time, or with light therapy. In this way too, psoriasis is a major burden, even when treatment works well and the psoriasis has become much less visible — you are constantly occupied with your skin. With understanding and support from family and a well-balanced treatment plan from the dermatologist, it is usually possible to bring psoriasis under control and make it bearable.

How is psoriasis treated?

Several types of treatment are available. Each treatment aims to suppress the symptoms; at present it is not yet possible to cure psoriasis. Broadly, treatments can be divided into three groups: local (topical) therapy with ointments, creams and lotions; light therapy; and systemic therapy. Treatments from the different groups are often combined. In all cases it is important, alongside the medicinal treatment, to care well for the skin with a moisturising ointment (many types are available without prescription).

Local (topical) therapy

Corticosteroids (“hormone ointments”) — widely used. Resembling the hormones made by the adrenal gland, they reduce inflammation and the thickness of the psoriasis patches; with strong corticosteroids it is often possible to calm the skin almost completely. They come in strength classes from class 1 (mild) to class 4 (very strong); for psoriasis the stronger classes (3 and 4) are generally used. There are ointments (for the evening), creams and emulsions (for daytime), lotions (for the scalp) and a corticosteroid-containing shampoo for the scalp (left on dry hair for 15 minutes, then washed out like a shampoo). Drawbacks: after prolonged use corticosteroids become less effective (tachyphylaxis) and the skin can become thinner (atrophy).
Calcitriol — a derivative of vitamin D3. Its mechanism is not fully understood, but it probably inhibits the production of skin cells and helps the cells that do form to develop better. It can be used for all forms of psoriasis, but is especially successful in psoriasis vulgaris and scalp psoriasis, can be combined with other treatments such as topical corticosteroids or light therapy, and can also be applied to psoriasis on the face.
Calcipotriol/betamethasone — an ointment or gel combining calcipotriol (a vitamin D derivative) and betamethasone (a corticosteroid). It only needs to be applied once a day to the patches according to your doctor’s schedule. The gel comes with an applicator and can be used on the body and the scalp; a spray-foam version is also available for use on the skin.
Dithranol — inhibits cell growth. Available in creams of different concentrations (from 0.05% to 3%); treatment usually starts at a low concentration and is slowly increased as needed to avoid local irritation. It can be used in all forms of psoriasis, including scalp psoriasis, and is often carried out in day-treatment centres. Drawbacks: skin irritation and purple/brown staining of the skin (temporary) or clothing (permanent).
Salicylic acid — psoriasis often has thick, white, firmly attached scaling. Applying active ointments on top of the scales is pointless because the active ingredient cannot then reach the skin cells. When there is a lot of scaling, it is therefore wise to loosen it first with salicylic acid, which softens the scales, before applying the active ointment.

Light therapy

PUVA — ultraviolet A (UVA) light is part of natural sunlight and penetrates fairly deep into the skin, influencing cell growth and skin inflammation. UVA alone is insufficient in psoriasis, so a medicine called psoralen is added to enhance its effect. Usually the psoralen is taken as tablets 1–2 hours before the light exposure; patients are treated about twice a week for several weeks to a few months. In some day-treatment centres “bath PUVA” is possible, in which the psoralen is dissolved in bath water rather than swallowed. Advantages: a proven, effective method, much easier than applying ointments in extensive psoriasis. Disadvantages: frequent light treatments increase the long-term risk of skin cancer; the psoralen tablets can cause nausea; and it is not suitable during pregnancy or breastfeeding.
UVB — also part of natural sunlight, with a more powerful effect than UVA, so it is used without additional oral medicines such as psoralen (although PUVA is more powerful than UVB). UVB penetrates less deeply, but is generally well suited to psoriasis. Newer narrow-band UVB lamps are almost as effective as PUVA. Advantages: proven and effective, much easier than ointments in extensive psoriasis, and can if necessary be used during pregnancy. Disadvantage: frequent light treatments increase the long-term risk of skin cancer.

Systemic therapy

For severe forms of psoriasis that cannot be controlled with topical treatments or light therapy, the dermatologist may propose systemic therapy. Monitoring and supervision of these therapies must always be carried out by the medical specialist. Options include:

Ciclosporin — suppresses the immune reaction involved in psoriasis. Advantages: easy to take, usually very effective. Disadvantages: can only be used for a limited period, and psoriasis can flare strongly again after stopping; many possible side effects are described, including raised blood pressure and kidney problems, so regular checks of blood and blood pressure are necessary.
Acitretin — resembles vitamin A acid and helps skin cells grow out normally again. Advantages: easy to take, usually once a day; it is one of the few therapies that can also help nail psoriasis and palmoplantar pustular psoriasis. Disadvantages: pregnancy is strictly forbidden until 2 years after stopping, as acitretin is very harmful to the unborn child; dry lips, skin and eyes can occur, and other side effects include raised blood cholesterol, nausea, headache and changes to the bones, so blood must be checked regularly.
Methotrexate — works by inhibiting cell division, which is increased in psoriasis. Advantages: easy to take, generally three times a week, and can also be given by injection. Disadvantages: cannot be used during pregnancy, and men taking it should not father children; it can suppress blood-cell production in the bone marrow and cause liver problems (long-term treatment sometimes requires a liver biopsy), among other described side effects.
Fumaric acid (fumarates) — a medicine used for many years, with relatively few side effects, so it is increasingly applied.
Apremilast — for severe psoriasis when the above treatments work insufficiently or are contraindicated. It is a selective suppressor of the immune system, inhibiting phosphodiesterase-4 (PDE-4) in inflammatory cells, which reduces the amount of cytokines (such as TNF-alpha, IL-23 and IL-17) that help drive psoriasis. It is taken as a tablet.

Biologics for psoriasis

An important development in treating more severe psoriasis was the arrival of “biologics” — medicines usually produced by recombinant techniques. Until recently these were used mainly for rheumatoid arthritis and psoriatic arthritis, but they can now also be prescribed for severe forms of “ordinary” plaque psoriasis. The dermatologist can prescribe them when other systemic therapies (such as ciclosporin and methotrexate) have already been tried. As with other systemic treatments, thorough information and supervision by your dermatologist are important; biologics are generally well tolerated. Some regularly prescribed biologics:

TNF-alpha inhibitors

Etanercept — binds to TNF (tumour necrosis factor), which plays an important role in the inflammatory reaction of psoriasis. TNF bound to etanercept cannot bind to the TNF receptor, so the inflammatory reaction does not get going. Given by injection.
Infliximab — an IgG1 monoclonal antibody that binds both the soluble and the transmembrane forms of TNF-alpha, preventing its harmful effects and inhibiting the inflammatory process. Given by infusion.
Adalimumab — also a TNF-alpha inhibitor, registered for both skin psoriasis and psoriatic arthritis. Given by injection every two weeks.
Certolizumab pegol — neutralises TNF-alpha, thereby suppressing psoriasis activity. Maintenance dose is one injection every two weeks.

Interleukin-17 inhibitors

Secukinumab — a monoclonal antibody that selectively neutralises IL-17A, which is found in large amounts in psoriasis-affected skin. Blocking IL-17A suppresses psoriasis activity in the skin.
Ixekizumab — also binds the cytokine interleukin-17A. At the start of treatment an injection is given every 2 weeks; from week 12 onwards, every 4 weeks.
Bimekizumab — a powerful inhibitor of interleukin-17F, which also plays an important role in psoriasis. After the start-up phase, one injection every 8 weeks can suffice.
Brodalumab — a human monoclonal antibody that selectively binds the interleukin-17 receptor A (IL-17RA), preventing binding of interleukin-17A and reducing skin inflammation. Maintenance dose is in principle one injection every 2 weeks.

Interleukin-23 inhibitors

Guselkumab — selectively blocks interleukin-23 (IL-23), one of the key proteins driving the inflammation that leads to psoriasis plaques. After a start-up dose and a repeat at 4 weeks, it is given in principle once every 8 weeks by injection.
Risankizumab — an anti-IL-23 antibody effective in psoriasis, given by injection.
Tildrakizumab — an inhibitor of interleukin-23. Maintenance treatment is generally one injection every 12 weeks.
Ustekinumab — for moderate to severe plaque psoriasis; an inhibitor of interleukins 12 and 23 (IL-12 and IL-23). After the start-up phase it is given in principle once every 12 weeks.

Frequently asked questions

Does pregnancy make psoriasis better or worse? Pregnancy can strongly influence psoriasis activity. During pregnancy the mother’s immune defences change to prevent the immune system from recognising the unborn baby as foreign. Since psoriasis is driven by the immune system, it is not surprising that these changes can alter its activity. Research shows that in about 56% of pregnant women the psoriasis improved, in just over 24% it worsened, and in about 18% it stayed the same. Unfortunately, many of those who improved during pregnancy noticed a worsening again after delivery.

Can a throat infection worsen psoriasis? Yes — an infection somewhere in the body can cause a flare of psoriasis. A throat infection with the streptococcus bacterium is particularly notorious. As the immune system mounts its defence against the bacterium, psoriasis patches can appear as a side effect of that reaction. Guttate psoriasis (with countless small scaly spots spread over the skin) is often seen after a throat infection. The infection is not the cause of psoriasis (which is genetically determined), but can be the trigger for an “explosion” of new patches.

What is the best medicine for psoriasis? Many medicines are available. The best one for you is the one that gives the best result with the fewest side effects — and finding that is a challenge to work out together with your dermatologist. It depends on the type of psoriasis (skin patches, scalp scaling, nails…), how extensive it is, your age, any wish to have children in the near future, and any other health problems alongside the psoriasis.

When to see a doctor

See a doctor if you develop persistent red, scaly patches, sudden widespread flares, nail changes or painful joints, if psoriasis is affecting your daily life or confidence, or to discuss which treatment best suits your situation.