Prurigo nodularis (PN), also known as nodular prurigo, is an inflammatory skin disease. It causes pruritus (intensely itchy skin) with skin nodules (bumps) and lesions. PN can look and feel similar to other skin conditions, making it tricky to diagnose.

Dermatologists use various tests to rule out other conditions and make a PN diagnosis. Receiving a correct diagnosis helps ensure you’ll get the treatment you need. Here’s what usually happens on the path to diagnose PN.

Challenges of Diagnosing Prurigo Nodularis

There’s a lot to consider before diagnosing PN. Your healthcare provider will start by reviewing your symptoms. Common PN symptoms may include:

• Extremely itchy skin episodes that are ongoing (sometimes lasting six weeks at a time)
• Thickening, lichenification (skin has become thickened and leathery), and scarring of the skin
• Burning or crawling sensation

Many of these symptoms overlap with other skin diseases. Sometimes, this leads to the wrong diagnosis. A misdiagnosis can lead to healthcare providers suggesting treatment options that don’t work or make symptoms worse.

If you have a skin condition and your treatment plan isn’t working, follow up with your doctor. Seek more testing to make sure you have the right diagnosis and an effective treatment plan.

Tests To Diagnose Prurigo Nodularis

Dermatologists may perform a few tests to closely examine your skin cells. If they suspect you have PN, they may also run blood tests to look at levels of different immune cells. Blood tests and stool tests screen for diseases or infections that could make PN symptoms worse.

PN often happens alongside other health conditions, known as comorbidities. If you have comorbidities that are contributing to PN, addressing these problems can help treat PN and improve your overall quality of life.

Physical Exam

In the diagnosis process, your primary care physician or dermatologist will start with a physical exam. They may also ask how your skin symptoms affect your daily activities, like going to school or work. They’ll ask questions to learn if your symptoms affect your sleep, mental health, social life, and quality of life.

After your discussion, your healthcare provider will look for signs of PN on your skin, like nodules, plaques, or papules. They’ll check if these are symmetrical (the same on both sides of the body). They’ll also take note of where the skin issues occur. Common sites for PN include the arms, legs, upper and lower back, and belly. Finally, your dermatologist may ask you to rate your itchiness on a scale from mild to very severe.

Dermoscopy

Dermatologists use a test called dermoscopy to look closely at the skin. This method has been traditionally used to diagnose types of skin cancer. However, it’s also useful for diagnosing other skin conditions such as PN. Dermoscopy is noninvasive, meaning it doesn’t break the skin. This lowers the risk of infection and PN flares.

Dermoscopy uses a high-powered magnifying lens that’s attached to a light (called a dermatoscope). The dermatologist places the lens onto a nodule or skin lesion. Then, they can inspect different skin layers, including the epidermis (outermost layer of skin) and the dermis (second-deepest skin layer), and look for any inflammation. They may also take pictures with the dermatoscope to look at later.

Dermatologists use the dermascope to check things like:

• Pigmentation (how light or dark the skin is)
• Amount of keratin (a protein found naturally in the skin)
• The symmetry of the nodules or lesions
• Vascularization (the blood vessels in the skin)

People with PN may have a distinct pattern in their lesions. A pearly white pattern with erosion surrounded by a dark-colored crust with excess keratin in the skin can help distinguish PN from other skin conditions.

Skin Biopsy

Another test used to diagnose PN is a skin biopsy. This is an invasive test. Your dermatologist removes a piece of skin so they can view it under a microscope. A skin biopsy can test a piece of thickened skin from a nodule or lesion that may be from PN.

There are three types of skin biopsies: excisional biopsy, shave biopsy, and punch biopsy. A shave biopsy removes the top skin layers. Punch and excisional biopsies go deeper and may require stitches afterward.

In people with PN, lesions tend to have more immune cells. Specifically, these include cells called macrophages, mast cells, and neutrophils. Immune cells cause skin inflammation, which leads to itchiness, discoloration, and swelling.

PN lesions and nodules may also have more keratin. People with PN tend to have hyperkeratinization (an excess of keratin). Constant itching and scratching make keratin build up over time.

The immune cells and keratin found in a skin biopsy will help your dermatologist make a PN diagnosis. Sometimes, the biopsy is diagnostic, meaning it helps the doctor decide whether you have PN. Other times, it supports a PN diagnosis, helping to confirm what’s already known about your skin.

Blood Tests

Tell your doctor if you have any underlying health or medical conditions. Certain conditions are associated with an increased risk of PN. Knowing about your medical history helps your healthcare provider better understand your health risks.

Blood tests look at levels of immune cells. They can also check your organ function. This information helps determine if another condition or infection is playing a role in your PN. Examples of tests your doctor may order include:

• Complete blood cell count with differential to check for infection (measures the number of red blood cells, white blood cells, and platelets in the blood)
• Kidney function tests
• Thyroid function tests
• Liver function tests
• Hemoglobin A1c to check for diabetes
• Screening for hepatitis B and hepatitis C and HIV or AIDS, which increase the risk of PN

Differential Diagnosis and Other Skin Conditions

PN often looks similar to other inflammatory skin conditions. These are known as differential diagnoses. Examples of skin conditions with similar symptoms include:

• Atopic dermatitis (the most common type of eczema) with lichen simplex chronicus
• Bullous pemphigoid or other blistering skin diseases
• Psoriasis
• Actinic prurigo, another chronically itchy skin condition

Dermatologists may have a difficult time diagnosing PN correctly since it appears similar to other diseases. Skin biopsies are especially useful for separating PN from other skin disorders. After a biopsy, the skin is sent to a pathology lab. There, it’s stained with different chemicals to look for certain proteins and immune cells.

Skin with PN tends to have more keratin versus skin affected by other conditions. It’s also higher in inflammatory cells and fibrosis (buildup of thickened or scarred skin). Dermatologists may also use skin scrapings on lesions or nodules to look for any signs of infection. They can also test these samples for diseases like scabies or fungus.

Diagnosing PN correctly helps ensure you receive the treatment you need to help manage your symptoms. An accurate diagnosis can help break the itch-scratch cycle. Your doctor may choose to run additional tests to identify and treat other health conditions that may be affecting your health and your skin.

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? What was your experience like when getting diagnosed? Share in the comments below, or start a conversation by posting on your Activities page.