Prurigo nodularis (PN) is a skin disease that causes hard, itchy lumps (nodules) to form on the skin. The itching (pruritus) can be intense, causing people to scratch themselves to the point of bleeding or pain. Scratching can cause more skin lesions to appear. The itching is worsened by heat, sweating, or irritation from clothing. In some cases, people with PN have a history of other diseases including eczema (atopic dermatitis), lymphoma, HIV infection, severe anemia, or kidney disease. 

The exact cause of PN is unknown. Although scratching is known to cause more nodules to appear, it is unclear what causes the itching to develop in the first place. Diagnosis of the disease is based on observing signs such as extremely itchy skin with the formation of nodules. In some cases, a skin biopsy is used to confirm the diagnosis. Treatment may include corticosteroid creams, oral medications, cryotherapy, or photochemotherapy.

The exact cause of prurigo nodularis (PN) is not well-understood. It is thought that nodules are more likely to form when skin has been scratched or irritated in some way. Therefore, the act of a person scratching skin can cause the nodules to form. However, the cause of the skin to originally become intensely itchy is unclear. Many people with PN have a history of eczema (atopic dermatitis), other skin conditions, or allergies. 

When people with PN have a skin biopsy, it can be seen that the nerves in the skin are thickened. It is thought that these thickened nerves may send stronger signals to the brain that the skin is itchy. This can cause a person to scratch the skin, which causes more nodules to form and the nerves to become even more thickened. This cycle, called the itch-scratch cycle, is thought to cause an increase in the number of nodules associated with PN. However, exactly why the skin becomes itchy in the first place is unclear and may vary from person to person. 

The main symptom of prurigo nodularis (PN) is the formation of hard, very itchy lumps (nodules) on the skin. The nodules can range in size from very small to about half an inch in diameter. The nodules often have a rough, dry top and can range in number from a few to hundreds. Nodules most commonly form on the outer arms, shoulders, and legs. Nodules can also form on the neck and trunk, and they rarely form on the face and palms. They may be lighter or darker in color than the surrounding skin. Scarring may occur after nodules begin to heal.  

The symptoms of PN can begin at any age but are most common in adults between 20-60 years. People who have PN may become very concerned about the appearance of the nodules, and the intensely itchy skin may interfere with sleep or with everyday activities. This can cause people with PN to develop stress and depression. 

Prurigo nodularis (PN) can be challenging to treat because people with the disease may respond to treatments differently. Due to the intensity of the itch, people with PN may try several different treatments without receiving much relief.  Some people may try all current treatments available without receiving complete relief. For most people, a combination of several treatments may need to be tried to find out what will work best.

The most commonly used treatments for PN are:

• Corticosteroid creams that are applied to the nodules (topical) and covered with special bandages that are air- and water-tight
• Corticosteroid injections into the nodules
• Ointments with menthol or phenol to cool and soothe itchy skin
• Capsaicin cream
• Oral corticosteroids
• Oral antihistamines
• Selective serotonin reuptake inhibitors (SSRIs)

If these treatments are not effective, other procedures may be used. These include cryotherapy, which uses very cold temperatures to try to reduce the size of the nodules, or laser therapy. Some people have used photochemotherapy, which combines the use of a medication that increases the skin’s sensitivity to ultraviolet (UV) rays with special light therapy. In some cases, immunosuppressants have been used to treat PN. If the lesions become infected, antibiotics or antibiotic ointment may be prescribed. 

All treatments are typically used in combination with habit reversal therapy, which aims to reduce the frequency of scratching the skin. This can be helpful in slowing down or stopping the cycle of itching and scratching that is associated with PN. Some people wear gloves while they sleep to reduce scratching. 

You can read further treatment information by visiting the American Osteopathic College of Dermatology (ACOD) information page on prurigo nodularis.

Although treatment options can help relieve itching and reduce the number of nodules, most people with prurigo nodularis (PN) do not have a complete resolution of the nodules even with treatment. The itching associated with the disease can be very intense, and it may affect the person’s ability to sleep at night or to enjoy everyday activities. This can result in increased stress and depression. It is important to speak with your doctor if you are having signs or symptoms of depression.

Prurigo nodularis may be suspected when a person has signs and symptoms of the disease including intensely itchy skin and the development of nodules on the skin. In some cases, a doctor may wish to perform a skin biopsy to look for signs of the disease such as thickened nerves in the skin. After the diagnosis has been confirmed, other tests such as a blood test and tests of liver and kidney function may be recommended to rule out underlying causes of the disease. 

In general, prurigo nodularis (PN) is not thought to be passed directly from parents to children. This is because changes in any one specific gene are not thought to cause PN. However, the development of PN is sometimes associated with having other skin diseases, allergies, or other health problems. Many people with PN also have family members who have these same health issues.

If family members of people who have PN have these other health concerns, it may be that they are at an increased risk to develop PN themselves. This is possibly related to shared environmental and genetic factors that cause the underlying skin disease.