Itching or Pruritus : Causes, Diagnosis, and Treatment

Itching is an unpleasant sensation of the skin that leads to a desire to rub or scratch the skin area so as to get relief. Itch is a major somatic sensation, along with pain, temperature, and touch.

Pruritus is the medical term for the itch.

Pruritus can be localized to a particular area of the skin or can be generalized.

Recent studies have suggested similarities between itch and pain. Both are unpleasant sensory experiences but the behavioral response patterns are different. Pain creates a withdrawal reflex, whereas itch causes a scratch reflex.

Unmyelinated nerve fibers for itch and pain both originate in the skin.

Skin serves as a barrier, protecting the inside of the body.

Read more about Skin Anatomy and Physiology

Cells of the immune system protect the body and skin from viruses, bacteria, and other hidden threats.

Any local reaction can trigger a rash or dermatitis and cause itching.

Itching could also be caused by a more serious condition such as liver disease or kidney failure.

Itch generates stimulus of a foreign object underneath or upon the skin and also the urge to remove it. [scratch reflex].

Itching is generally relieved by scratching.

However, in some cases, the pleasure associated with scratching may lead to the compulsive nature of itch and scratching.

Many cases of itching are mild and can be treated by self-care and regular moisturization of the skin. However, a few cases require detailed investigations to find the exact cause and also warrant a proper medical treatment.

Pruritus or Itching — Image credit: wikipedia.org

Types of Itching

Dermal

It is also called pruritoceptive and can be induced by a variety of stimuli. The primary afferent neurons responsible for histamine-induced itch are unmyelinated C-fibres.

Itch receptors are found only on the top two skin layers, the epidermis, and the epidermal/dermal transition layers. Sensitivity to pruritic stimuli is evenly distributed across the skin.

Neuropathic

Neuropathic itch can originate at any point along the afferent pathway as a result of damage of the nervous system. Examples of neuropathic itch in origin are brachioradial pruritus, brain tumors, multiple sclerosis, peripheral neuropathy, and nerve irritation.

Neurogenic

Neurogenic itch is itch induced centrally but with no neural damage. It is mostly associated with increased accumulation of exogenous opioids.

Psychogenic

It is found in psychiatric disorders such as tactile hallucinations.

Mechanisms of Itching or Pruritus

Peripheral Mechanisms

Physical Stimuli and Neural Pathways

The itch can occur as a result of mechanical stimuli (gentle touch, pressure, etc), thermal stimuli (heat) or electrical stimuli (transcutaneous or direct nerve stimulation). This stimulus or sensation is received by free nerve endings present in the skin and transmitted through unmyelinated C fibers and myelinated Aδ fibers to the central spinothalamic tracts. Neural pathways for transmission of pain and itch are separate.

Chemical Mediators

A number of chemicals have been implicated for causing the itch. The most important of these is histamine released from mast cells. Others include neuropeptides which also act by releasing histamine. All such conditions can be treated by antihistamines. Certain chemical mediators act independently.

Central Mechanism

Certain lesions of the central nervous system produce an intractable pruritus.(hard to control pruritus). Opioids administration can also cause pruritus through central action.

Causes of Itching or Pruritus

Skin Diseases

Dry skin (xerosis)
Eczema (atopic dermatitis)
Contact dermatitis
Allergies (to wool, chemicals, soaps, certain foods, poison ivy, cosmetics, etc)
Hives
Insect bites
Psoriasis
Dermatitis herpetiformis
Lichen simplex chronicus
Lichen planus
Scabies
Burns
Scars
Fungal infections
Pediculosis
Sunburn
Polymorphous light eruption
Pityriasis rosea

Systemic causes

Chronic renal failure
Liver disorders
- Hepatic cholestasis
- Primary biliary cirrhosis
- Cholestasis of pregnancy
- Oral contraceptives
- Extrahepatic biliary obstruction
- Hepatitis
- Drugs
Hematopoietic disorders
- Polycythemia vera
- Hodgkin’s disease
- Multiple myeloma
- Mastocytosis
- Iron deficiency anemia
Endocrine
- Thyrotoxicosis
- Hypothyroidism
- Carcinoid
Miscellaneous
- Drug reaction to opioids
Nerve disorders
- Multiple sclerosis
- Diabetes
- Herpes zoster or shingles
Psychiatric diseases
- Depression
- Anxiety
- Obsessive-compulsive disorder
Pregnancy
- Gestational pemphigoid
- Intrahepatic cholestasis of pregnancy
- Pruritic urticarial papules and plaques of pregnancy (PUPPP)
Stress

Complications

Chronic pruritus (that lasts for more than six weeks) can have a significant effect on the quality of life.

It can cause sleep interruption. It can also lead to anxiety or depression.

Prolonged itching may lead to skin injury, infection, and scarring.

Diagnosis

A careful history is a must for arriving at the correct diagnosis. The following points should be asked or assessed:

Severity and quality of the itching
Sites of itching
The extent of itching (localized or generalized)
Aggravating or relieving factors
Diurnal or seasonal variations
Effect of environmental factors
Known allergies
Family history of allergy (eczema, allergic rhinitis or asthma)
Overall psychological state and well being of the patient
Degree of disruption of the patient’s lifestyle

Physical examination

The skin should be carefully examined to detect any obvious disorder. Intense scratching of the skin can cause secondary changes in the skin like excoriations, papules, nodules, or lichenified plaques. These secondary changes must be distinguished from the primary skin lesion. Evidence of parasitic infestation, such as scabies and lice should be sought for.

Investigations

In many cases, the diagnosis becomes apparent from the history and physical examination. When the diagnosis is not apparent, laboratory investigations may be carried out.

Some basic and initial investigations which may be carried out include:

Complete blood count
Erythrocyte sedimentation rate or ESR
Blood urea nitrogen, creatinine: to detect kidney disorders
Liver function tests: to rule out liver disorders
Fasting glucose, HbA1C: to exclude diabetes mellitus
Thyroid function tests (T3, T4, TSH)
Tests for hepatitis B and C

Depending upon the initial results and the features of the disease, further investigations may be carried out.

HIV screening
Serum iron and ferritin
Serum calcium and phosphate levels
Serum and urine protein electrophoresis
Stool for occult blood, ova, and parasites
Skin biopsy with immunofluorescence
Upper and/or lower endoscopy
Chest x-ray: to rule out mediastinal lymphoma
Computed tomography or CAT scan

In a patient suspected of having an allergy, the panel of investigations includes:

Total IgE level
Prick testing, patch testing
Histamine levels
Mast cell metabolites
Serotonin
Urine 5-HIAA
Antinuclear antibody
Antimitochondrial antibodies
Antitissue transglutaminase antibodies

Treatment of Itching or Pruritus

Finding the cause of itching and treating the underlying cause is the first step of treatment.

Self-care tips and home remedies

Avoid the substance which is causing itching.

If itching is due to a drug reaction, stop that medicine and switch to a different drug.

If you are allergic to a known substance, like a particular soap or cream, avoid it completely.

The best way to prevent pruritus is to take care of your skin. To protect the skin:

Use skin creams or emollients to moisturize your skin and prevent dryness.
Avoid frequent baths.
Use lukewarm water for bathing in cold weather. Do not use hot water as it irritates the skin.
Oatmeal can be added to water for bathing.
Use a mild soap for bathing. The soap used should not rob the skin of its natural moisture or irritate your skin.
Cleansing agents or soaps used should have a low pH so as to maintain the acidic pH of the skin. This helps to preserve the skin barrier function and reduces skin irritation.
Use sunscreens when out in the sun to prevent sunburns and skin damage.
Avoid fabrics that irritate the skin, such as wool and synthetics. Use cotton clothing and bedsheets. Even in winters, do not let the woolen clothes come in direct contact with the skin. Always wear a layer of cotton clothing underneath the woolens.
Always wear light and loose-fitting clothes. Avoid wearing tight or restrictive garments.
Warm and dry air tends to make the skin dry. So avoid excess use of heaters or air conditioners. You can also use a humidifier to prevent the air from becoming dry.
Avoid hot or spicy foods or alcoholic beverages as these foods can induce histamine secretion.
Resist the temptation to scratch your skin.
Keep your fingernails short. This may prevent damage to the skin if you can’t resist the urge to scratch
To relieve itching, place a cool cloth or some ice over the skin that itches.
Cooling lotions like calamine, menthol, and camphor provide a soothing effect to the irritable skin. They stimulate the nerve fibers which transmit the sensation of cold, and hence mask the itchy sensation.

If home remedies are unable to relieve the itch, prescription medicines or other treatments may be recommended.

Local corticosteroid creams and ointments help to relieve the itch or inflammation associated with it. They should not, however, be used to treat generalized itch all over the body. Also, they should not be used for a long time as they can cause side effects such as skin atrophy, skin eruptions, and dryness.

Topical or oral antibiotics may be used to treat skin infections associated with intense itching.
Topical antihistamines or H1 receptor blockers such as doxepin are effective antipruritics in conditions such as urticaria and insect bites.
Oral antihistamines are the drugs of choice for urticaria. The newer nonsedating antihistamines are less effective in atopic dermatitis as compared to older sedating antihistamines. Sedating antihistamines are also beneficial in patients with nocturnal pruritus.
Topical tacrolimus is an immunomodulator that helps to reduce inflammation and decreases itch. It is useful in atopic dermatitis. Its role in other causes of pruritis is not clear.
Topical anesthetics such as pramoxine and EMLA (eutectic mixture of local anesthetics) cream also produce an antipruritic effect in mild to moderate pruritus.
Topical capsaicin may be useful in intractable pruritus at a localized site. It acts by desensitizing nerve endings that are responsible for causing the itch. Localized burning and stinging sensation may occur as a side effect. This side effect subsides with repeated use of capsaicin or by the use of topical anesthetic (EMLA cream).
Antidepressants called selective serotonin reuptake inhibitors (SSRI), such as fluoxetine (Prozac) and sertraline (Zoloft), may be useful in some types of chronic itch.
Gabapentin which is an antiepileptic drug is useful in neurogenic pruritus, uremic, hematologic, and idiopathic pruritus.
Tricyclic antidepressants such as doxepin produce both central effects as well as antihistaminic effects and are also useful in chronic cases of pruritus.
Opioid antagonists such as naloxone, have occasionally been used for intractable pruritus of renal and cholestatic diseases.
Light therapy. In this, the skin is exposed to a specific type of light. It may require multiple sittings to be effective. Ultraviolet (UV) B phototherapy is useful in pruritus associated with renal disease, atopic dermatitis, HIV infection, etc.

Chronic Renal Disease

First-line therapy includes UVB phototherapy and erythropoietin

Capsaicin 0.025% cream, tacrolimus 0.03% ointment, gabapentin cream are also effective. Dialysis is also helpful. Insufficient dialysis leads to increased severity of pruritus.

Second-line therapy includes oral activated charcoal, cholestyramine, and the opioid antagonist naltrexone.

The Third-line of treatment includes thalidomide and parathyroidectomy.

Renal transplantation is the definitive treatment.

Cholestatic Disease

Cholestyramine is the first-line of treatment. It acts by lowering the levels of bile salts and other pruritogens. The second line of therapy includes rifampin, opioid antagonists such as naloxone and naltrexone, and SSRI.

Other treatments include UVB phototherapy, plasmapheresis, and dronabinol (a cannabinoid).

Ursodeoxycholic acid has a role in pruritus in women with cholestasis of pregnancy.

Extracorporeal albumin dialysis may be considered in pruritus which is refractory to other therapies.

Ondansetron is used to treat opioid-induced pruritus.

Removal of the offending medicine is a must for treating patients with drug-induced cholestasis.

Hematologic pruritus

Iron deficiency anemia requires treatment with iron.

Read more about Dietary Iron Requirement and Sources

Correction of iron deficiency in patients with polycythemia vera helps to treat pruritis but worsens the polycythemia vera. Aspirin is the first-line treatment in polycythemia vera. Cimetidine, cholestyramine, danazol, UV-B light therapy, and psoralen with UV-A therapy are also effective for pruritis in polycythemia vera.

Thalidomide has been shown to be effective in severe pruritis due to Hodgkin disease. In the late stages of Hodgkin disease, corticosteroids along with palliative chemotherapy have proved to be beneficial.

Paroxetine is useful in controlling itching in patients with advanced-stage cancer. However, its effect lasts for only 4-6 weeks.

Endocrine pruritus

In hypothyroidism, pruritis occurs due to xerosis and responds to treatment with emollients and thyroid hormone replacement.

Pruritis secondary to hyperthyroidism responds once the thyroid function is corrected.

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