What about itching?
The medical term for itching is “pruritus”. The sensation can be limited to one area of the skin or extend over the whole body. There are numerous causes for itching, such as inflammatory skin conditions or general illnesses. Psoriasis was long believed to be non-pruritic (non-itchy) and not all patients with psoriasis are suffering from itchyness. However, several studies have shown that 80% of patients with psoriasis do experience it. There are varying degrees of itchiness, measured using visual analogue scales.
Patients indicate the severity of their itching on a scale from one to 10 (from moderate pruritus to severe pruritus where patients scratch plaques until they bleed). Itching causes a vicious circle, as scratching leads to the hypertrophy (enlargement) of cutaneous nerve endings, which in turn become more sensitive.
In addition, excessive scratching leads to the brain reacting to any external stimulation by causing a sensation of itching. Scratching is a type of trauma, and psoriatic lesions frequently appear in traumatised areas, in a response known as the Koebner phenomenon.
Do itching and pain have anything in common?
Much less is known about the brain centres involved in itching than those involved in pain. Some researchers believe that neurotransmitters play an important role in itching. Itching and pain do have some features in common. They are both unpleasant sensations, and information is transmitted along the same neural pathways.
Information is transmitted by the first neuron to the spinal cord, then a second neuron transmits it to the thalamus (at the base of the brain) and a third relays it to the cortex (the conscious brain). The patient becomes conscious of pain and itching after a certain threshold level has been passed, which varies according to psychological factors, such as stress and depression. Stress aggravates itching.
Moreover, studies have shown that in people suffering from depression, there is a correlation between the degree of itchiness and the degree of depression. Itching therefore causes real physical and psychological suffering, just as pain does.
What drugs are available for itching?
First and foremost, the psoriatic lesions need to be treated. Topical corticosteroids, UVA and UVB rays and cyclosporin frequently decrease itching. However, in cases where these therapies have been unsuccessful, it becomes difficult to stop itching. Although antihistamines prevent itching in some conditions, they do not appear to be effective in treating the itchiness caused by psoriasis.
Patients suffering from depression or anxiety who also suffer from itching should receive therapy which specifically targets their psychological problems.
Can other treatments help?
Applying moisturising lotion once or several times a day can help to soothe the skin as it counteracts dryness. Spa treatments may also be beneficial as some thermal mineral water has anti-inflammatory properties and reduces itching. Stressed and depressed patients may also find relaxation techniques, such as sophrology and yoga, helpful to combat anxiety and so decrease itchiness.
Friction and minor skin trauma can provoke lesions, so natural fibres, such as cotton, should be worn. Very hot showers and baths should also be avoided, and only mild skin care products should be used. Gloves are useful for limiting exposure to strong detergents. It is better to cut nails short to minimise damage caused by scratching. Finally, alcohol and coffee should be avoided.
With thanks to Dr Laurent Misery, dermatologist at Brest University Hospital and author of La Peau neuronale, published by Ellipses.