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Pruritus: causes and treatment options for itching

Itching (pruritus) is defined as a skin-specific sensation triggered by different stimuli that provokes mechanical defense reactions such as rubbing, scratching or cooling. Those affected find pruritus annoying to excruciating. It can lead to a significant loss of quality of life, to sleep disorders, decreased performance and even to physical and psychological exhaustion.

Itching is not a pain variant

While some time ago it was assumed that itching was a sub-form of pain, we now know that it is an independent sensation. This is also anatomically evident in the form of the specific, epidermally localized nociceptors and a separate conduit system made of unmyelinated C-fibers.

Therefore z. B. After the loss of the epidermis, pain continues but no itching can be perceived. The two sensory perceptions can also be differentiated pharmacologically: while opioids can be used to suppress pain, itching cannot be suppressed, on the contrary: Opioids are often even responsible for inducing itching.

Interplay of different influences

The classic and best-researched endogenous itching mediator is histamine. It plays a central role, especially in urticaria. Endorphins and prostaglandins are able to potentiate the histamine effects. Another important biogenic amine in the itching process is serotonin. In aquagenic pruritus, i.e. itching after contact with water, serotonin seems to play the main role. In addition, various proteases, the Proopiomelanocortin system (POMC) and neuropeptides such. B. the substance P - a potent histamine liberator - of pathophysiological interest.

The variety of pruritogenic factors known to date makes it understandable that one cannot speak of the itching. Rather, different pruritus forms occur in different diseases associated with pruritus, depending on the mediator pattern. The chance for a causal pruritus therapy is therefore slim. Most of the time, only symptomatic treatment can be carried out.

Itching and medication

In contrast to pain therapy, for which a step scheme recommended by the WHO has now been established, there is no comparable concept for the treatment of itching. To make matters worse, itching is difficult to quantify. So far, mainly visual analog scales have been used for this. However, their informative value is limited, which also complicates the development of evidence-based therapy concepts.

One of the few cases in which the itching can be dealt with causally is drug-induced pruritus. B. Captopril, codeine, miconazole, clonidine, propafenone, pyritinol, tramadol, tilidine, bleomycin or gold preparations can cause skin itching as a side effect. After intravenous administration of hydroxyethyl starch (HAES), generalized itching occurs in some patients only after a latency period of up to 6 weeks. It is not known which pathomechanism is behind these phenomena.

Itchy skin as a counseling topic

Any kind of itchy skin, regardless of its origin, can be alleviated through certain behavioral and care measures. This includes:

  • wearing light clothing, preferably made of cotton (no wool!)
  • regular skin care with - depending on the skin type - rehydrating or moisturizing topicals. Medicinal oil baths with soybean oil (e.g. Balneum Hermal®) or peanut oil (Cordes oil bath®) are recommended. However, the water temperature should not exceed 35 ° C so that the skin's own lipid film is not further damaged.
  • Do not practice excessive personal hygiene, do not shower or bathe too long, not too hot and not too often
  • Set up humidifiers in the rooms so that the skin does not dry out
  • wear light cotton gloves if you scratch at night

In addition, there is a wide range of preparations available for self-medication:

  • over-the-counter cortisone ointments (e.g. Ebenol®, Soventol® HC)
  • Topicals containing local anesthetics (e.g. anesthesia® Ointment, labocane®)
  • topical antihistamines (Fenistil®, Systral®, Tavegil®)
  • oral H1 antagonists (e.g. preparations containing loratadine or cetirizine)
  • Tanning preparations (e.g. Tannosynt®, Tannolact®)

In addition, the recipe fundus of every pharmacy z. B. with Unguentum leniens, Lotio alba aquosa or Polidocanol-containing preparations (approx. 5%, finished preparation e.g. Anaesthesulf®) further options for over-the-counter sales. In acute cases, those suffering from itching can also be helped by cooling compresses made of cotton rags that have previously been dipped in cold water. With dry skin, however, greasy dressings should be preferred: To protect the skin from drying out, a fatty ointment is first applied and the moist dressing is then placed over it.

Itching classics: urticaria and neurodermatitis

The most promising diagnosis and therapy are acute urticaria (hives). Typical urticaria triggers are drugs or food, especially food additives. Urticaria is pathophysiologically characterized by histamine effects. Therefore, the use of oral H1 antagonists is usually successful here. Today, modern, non-sedating antihistamines such as loratadine and cetirizine are preferred.

However, some doctors deliberately use the older sedating substances such as dimetinden (e.g. Fenistil), especially for children, before going to bed®) or Clemastine (Tavegil®) to prevent nightly scratching attacks.

The current treatment options for chronic urticaria are far less promising. The actual pathomechanism is largely unknown here, but it is suspected that autoimmune phenomena are the basis. Therefore, in severe cases, the oral immunosuppressant ciclosporin A and immunoglobulins are given.

Topical corticoids for atopic dermatitis

In the treatment of itching in the context of atopic eczema, the focus is on downregulating the inflammatory processes in the skin. The modern topical corticoids are primarily used for this purpose. Although potent substances with a favorable side effect profile are available today, these pharmaceuticals are only used for a limited time whenever possible and are not used on a large scale in children.

In severe atopic dermatitis cases, systemic corticoids, ciclosporin A or the recently approved topical immunomodulator tacrolimus (Protopic®Ointment). Since the oral antihistamines in addition to their H1 antagonism also have anti-inflammatory properties by z. B. inhibit the release of leukotriene and interleukin or suppress the expression of adhesion molecules such as ICAM-1, they are also useful for adjuvant treatment.

Itching also occurs with internal diseases

As a rule, several medicinal substances must be combined to effectively treat itching. This also applies to the types of pruritus associated with internal diseases. In cholestatic liver diseases, the itching probably arises when bile salts come into contact with macrophages and epidermal proteins. Since bile acids are bound by taking cholestyramine, the cholestatic itching can also be alleviated in this way.

Uraemic pruritus occurs in people with impaired kidney function, particularly those with terminal kidney disease. Here, on the one hand, the sebostatic skin of these patients and, on the other hand, their greatly increased histamine and substance P values, are responsible for the itching. Both UVB phototherapy and parenteral erythropoietin administration have proven helpful in uremic pruritus, which can lower the histamine level in the blood.

A causal therapy of uremic pruritus is only possible with a kidney transplant, after which the itching then disappears suddenly. Diabetics too often have to struggle with annoying itching. The causes are often dry skin and the well-known diabetes-related tendency to bacterial or mycotic skin infections, which can, however, be effectively countered with appropriate anti-infectives.

Experience has shown that malignant diseases such as tumors, lymphomas and leukemia are often accompanied by pruritus. A quarter of Hodgkin's disease patients suffer from itchy skin. It is noteworthy that the skin symptoms often precede the malignant disease several years. The pathophysiological relationships are unknown.

Antipruriginous exotic species

In addition to the drugs mentioned so far, other substances are used against itching in everyday clinical practice, even if there is no corresponding approval for most of them. Topical capsaicin, an ingredient of cayenne pepper with an anti-rheumatic effect, has also proven itself to alleviate various forms of itching.

After topical application, a burning sensation with vasodilation initially arises; With repeated use of a capsaicin ointment, the substance P stores of the C fibers are emptied, whereby the itching is suppressed. Capsaicin is a good alternative, especially for renal and cholestatic pruritus.

Antihistamines used to treat itching

The opiate antagonists naltrexone and naloxone also calm itchy skin. These substances antagonize the effect of endorphins, which act as histamine enhancers and are indirectly involved in itching. However, the widespread use of opiate antagonists against itching is not medically justifiable.

The tricyclic antidepressant doxepin (Aponal®) is also an effective histamine receptor antagonist and is therefore also used in higher doses for treating itching. Some time ago there were also antipruriginous effects with serotonin antagonists, especially ondansetron (Zofran®) has been observed. According to the literature, the prostaglandin synthesis inhibitor acetylsalicylic acid is effective in uritis during pregnancy and is allegedly even superior to antihistamines.

literature

Wassiliew, S. W .: Itching: A Diagnostic and Therapeutic Crux; German Doctor bl. 16, 1096-1102 (2002). www.aerztezeitung.de (Pruritus: What triggers scratching rage, 07.09.2001) imsdd.meb.uni-bonn.de/cancernet

Box text Internal diseases that are often associated with itching

  • Cholestatic liver disease
  • Uremia
  • Haematological Diseases
  • Malignancies
  • Infectious diseases
  • Rheumatic diseases
  • Endocrinological disorders

Box itching - a vicious circle

From a medical point of view, itching is a reflex: a stimulus in or on the skin is usually answered with scratching or rubbing. This stimulates the skin's inflammatory reactions, releasing histamine and other inflammatory mediators. These also lead to a stimulus to the mediating nerve endings - existing itching is further intensified.

Scratching can cause minor injuries to the skin. Foreign substances or bacteria penetrate the skin and cause infection. This also triggers itching, so that the vicious cycle of itching - scratching - inflammatory processes - itching ... - starts, which is difficult to interrupt.