Prurigo nodularis (PN), or nodular prurigo, is an inflammatory skin disorder that is often caused by other health conditions that lead to pruritus (itching). Frequent scratching can cause PN nodules to form, leading to even more itching. This process is known as the itch-scratch cycle. Treating other itch-causing medical conditions is an important part of managing PN.

People with PN may develop other disorders as a result of their PN. These conditions may require additional types of treatment.

Prurigo Nodularis Comorbidities

When someone has two or more health conditions at the same time, the conditions are known as comorbidities. Up to 9 out of 10 people with PN may have comorbidities that need to be treated alongside PN.

Skin Conditions

A study in the journal Acta Dermato Venereologica showed that in half of cases, PN develops after another skin disease that causes the skin to itch. Per the American Academy of Dermatology Association, people with the following conditions have a higher risk of getting PN:

• Atopic dermatitis (eczema) — Skin inflammation leading to dry, thickened, itchy skin
• Contact dermatitis — A rash caused by coming into contact with something that causes irritation or triggers allergies (such as poison ivy)
• Stasis dermatitis — Poor circulation in the legs leading to inflammation and swelling
• Bullous pemphigoid — A chronic skin condition that causes large, fluid-filled blisters or welts
• Lichen planus — An immune system reaction that causes flat, itchy bumps on the skin
• Scabies — A very itchy rash caused by skin mites
• Xerosis cutis — Extremely dry skin that can lead to itching, cracking, or flaking

Treating these conditions and keeping itching under control may help you avoid developing PN and PN symptoms.

PN can also occur at the same time as other skin conditions. In some cases, people may be incorrectly diagnosed with one of these conditions rather than PN because they all have similar symptoms. These related skin disorders include:

• Psoriasis — Skin cells build up and form scales and itchy, dry patches
• Pemphigoid nodularis — A rare type of bullous pemphigoid with nodular prurigo-like lesions and pemphigoid blisters
• Lichen simplex chronicus — A condition that starts with an itchy patch of skin with dry areas that are scaly and thick
• Lupus erythematosus — An ongoing disease in which the immune system attacks its own tissues

Tests like skin biopsies allow doctors to study a piece of skin more closely to tell these different conditions apart.

Allergies

Some people have gene changes that make them more likely to have allergies or other related conditions like asthma and hay fever. All of these conditions have been linked to an overactive immune system, which is one of the possible causes of PN. Those who have allergies or asthma are more likely to develop PN.

Infections

Certain infections can cause itching that leads to PN. Viral infections that increase PN risk include hepatitis C, herpes zoster, or HIV. Bacterial infections like tuberculosis, Helicobacter pylori, and mucogenicum can also cause PN. Finally, PN may develop after an infection with parasites like ascaris or strongyloidiasis.

If your doctor diagnoses you with PN, they may also recommend tests to check for an infection.

Heart and Lung Diseases

People with PN are more likely to have conditions that affect the heart and lungs. Heart problems linked to PN include hypertension (high blood pressure), coronary artery disease (hardening of the arteries), and heart failure (when the heart can’t pump enough blood).

Chronic obstructive pulmonary disease (often referred to as COPD), an inflammation of the lungs or airways, is also more likely to occur in people with PN.

Cancer

Some people develop PN as a result of cancer or its treatments. Cancers that affect blood cells are one possible cause. These include:

• Lymphoma, including Hodgkin lymphoma, non-Hodgkin lymphoma, and cutaneous T-cell lymphoma
• Leukemia, including a type of leukemia called polycythemia vera
• Multiple myeloma
• Myelodysplastic syndrome

Precancerous blood conditions can also lead to PN. One such condition, monoclonal gammopathy of undetermined significance (MGUS), is a noncancerous condition that can lead to multiple myeloma.

PN may also be caused by other types of cancer, such as skin cancer, lung cancer, cancer of the intestines or colon, breast cancer, head and neck cancer, bladder cancer, and reproductive cancers such as vaginal cancer.

Drugs to treat cancer, such as carboplatin (Paraplatin), paclitaxel (Taxol), and pembrolizumab (Keytruda), can also increase the risk of PN.

Neurological Conditions

The nervous system, including the brain, spinal cord, and nerves, also seems to play a role in PN. In some cases, damage to the nerves may cause itching and make PN more likely to develop. Herpes infections, shingles infections, itching after a burn, and neuropathies (problems with nerves that lead to tingling, numbness, or pain) can all cause this type of damage that leads to intense itching. The scratching itself may affect the nerves.

Other Comorbidities

PN has also been linked to a variety of other conditions:

• Diabetes
• Gout (a type of arthritis in which the immune system attacks the joints)
• Anemia (low red blood cell levels)
• Kidney disease
• Liver disease
• Thyroid conditions
• Overactive parathyroid glands
• An overactive pituitary gland
• Amyloidosis (a condition when abnormal proteins build up in the body)
• Celiac disease (a condition in which the intestines become damaged after eating gluten)

If you don’t know what is causing your PN, you may need tests to look for underlying health problems. Basic blood tests can show how well your kidneys, liver, and thyroid are working and determine whether you might have a condition like diabetes. Additional tests may be needed if your doctor thinks you might have another disorder. In many cases, no underlying cause is identified.

Psychological Conditions

In rare cases, conditions like anxiety, depression, and dissociative disorders can be associated with intense itching that causes PN.

Prurigo Nodularis Complications

When someone develops a medical problem as a result of another condition, it is known as a complication. PN can cause complications. Treating PN may help improve these conditions or make them easier to deal with.

Infected Nodules

Scratching too much can cause skin lesions (abnormal skin changes) to break open, which allows germs to enter the skin. This can lead to an infection, which may require more treatment options such as topical and oral antibiotics.

Sleeping Difficulties

Many people with PN have more severe itching symptoms at night, which can make it hard to fall or stay asleep. This may lead to sleeping problems and tiredness during the day.

In one recent study from the journal Acta Dermato Venereologica, 7 out of 10 people with PN said that their condition got in the way of their sleep to a moderate or large extent. Treating PN and reducing itching often helps people sleep better.

Mental Health Changes

PN can also affect your mental health. Some people with the condition may feel differently about their skin and body image. Symptoms of PN occasionally cause people to miss work, school, or social activities. Some may have a harder time following their usual daily routines. This happens often when a person is not sleeping well at night.

These and other factors can play a role in developing mental health conditions like depression or anxiety disorders. One study found that nearly half of people with PN currently or previously had a mental health condition.

Talk to your health care team if you’re noticing any mood or behavior changes, or if you find yourself avoiding things you used to enjoy. Various treatments, including antidepressants or counseling, can help treat anxiety and depression and improve your mental well-being.

The Impact of Comorbidities and Complications

Having comorbidities and complications may make it harder to deal with PN. You may be experiencing symptoms from a comorbidity along with PN symptoms such as severe itching.

Work with your primary and dermatology health care teams to make sure any underlying medical issues are being treated. Managing these other conditions may help treat your PN, prevent new nodules from forming, and improve your quality of life.

Find Your Team

MyPrurigoTeam is the social network for people with prurigo nodularis and their loved ones. On MyPrurigoTeam, members from all over the world come together to ask questions, give advice, and share their experiences with others who understand life with prurigo nodularis.

Do you have prurigo nodularis? Share your experience in the comments below, or start a conversation by posting on your Activities page.