What Is Prurigo Nodularis

Introduction

Prurigo nodularis (PN) is a chronic and debilitating skin condition where the skin breaks out into extremely itchy nodules. PN mainly affects the arms and legs but can be found anywhere on the body. They are typically a few millimetres to 2 centimetres across and can range in number from just a few to hundreds spread across the body.¹ 

PN poses a considerable challenge for both patients and healthcare professionals as it is a persistent and difficult-to-treat condition.¹ PN can be an extremely uncomfortable condition for patients to have to endure, with the compulsion to itch only worsening the condition, and the nodules, subsequent hyperpigmented macules, and scarring all potentially impacting the patient's body image and self-esteem.

Thankfully, research into the mechanisms associated with the disease is ongoing, which will give pharmacologists the much-needed insight to create new and innovative treatments. Currently, there is a plethora of ointments and treatment methods to quell the intense itchiness associated with PN, but the biggest thing you can do to help manage the disease is to restrain from itching.¹ While the exact cause of PN remains elusive, it is believed to involve a complex interplay of environmental factors and be associated with several other diseases.^2,3 In this article, we will delve into the intricacies of PN, examining its symptoms, potential causes, diagnostic approaches, available treatments, and the impact on patients' lives.

Symptoms and clinical presentation

Prurigo Nodularis has a very distinct clinical presentation that can be broken down into three key features.

Pruritus

Pruritus, also known as an itching feeling, is necessary for a diagnosis of PN. This sensation can be very intense, and some patients describe it as burning or stinging.⁴ This is often the start of the “itch-scratch” cycle that is very difficult for patients to break, leading to the perpetuation of the disease.¹ Excoriation, a disorder where you can not stop picking your skin, is a very common secondary symptom which can result in bleeding and scarring of the skin.⁵

Nodules and lesions

Nodules, ranging in size from a few millimetres to 2 centimetres, emerge as a consequence of repetitive scratching and represent a defining feature of PN. They are often hyperkeratotic, where the skin thickens and appears dry and scaly, sometimes changing colour.⁴ They are predominantly located on the arms and legs but are seen on the main body and sometimes on the face.¹ These nodules and lesions can be a huge source of stress for patients, affecting the patient's appearance and, subsequently, their mental health.

Skin changes

Whilst the skin between the nodules generally remains normal, it can sometimes show signs of dryness or lichenification (where the skin becomes thick and leathery). Additionally, the skin may show post-inflammatory hyperpigmentation, where, after damage, the skin makes extra melanin, causing dark spots.

Causes and risk factors

PN is a complex condition with its underlying causes still eluding scientists. Recent research suggests that the disease may be influenced by neurological factors and the immune response.⁴ Neuronal hyperplasia (damage to nerve tissue) has long been found in the skin of PN patients, with further studies looking for specific markers to uncover why this is the case.⁶ Additionally, histopathologic studies looking at the abundance of immune cells in PN nodules have cited IL-31 as the mechanistic cause of itching in PN.^6,7 These underlying mechanisms may be why PN is associated with certain diseases like hepatitis and HIV.¹

There are several risk factors associated with PN, including environmental triggers, such as insect bites and exposure to certain irritants, which may exacerbate symptoms. Additionally, PN seems to be most prevalent in people ages 51 to 65 years old.⁸

Diagnosis

To diagnose PN, a thorough clinical examination, including a review of symptoms potentially linked to other diseases, is crucial. Medical professionals will likely look at the severity of PN, considering factors like itching intensity and its impact on quality of life (sleep, anxiety, and depression should be assessed).⁹ 

A series of laboratory tests will then likely be conducted, including a complete blood count and liver/renal function tests. Additional screenings for thyroid function, diabetes, and infectious diseases like HIV and hepatitis B and C are advised based on risk factors and symptoms.⁹ Clinicians may also evaluate the need for emotional support during the initial visit and consider psychological comorbidities in subsequent visits. 

Persistent pruritus for over a year without other systemic symptoms is unlikely to indicate cancer, but rare cases may require additional screening.⁹ Patients should then undergo routine care and appointments for cancer screenings.

PN) can be confused with various skin conditions, including Kyrle's disease, hypertrophic lichen planus, autoimmune blistering diseases, and neurotic excoriations. To differentiate PN from these, a skin biopsy is recommended, examining the collagen and immune system.⁹

Treatment and management

One of the best ways to manage PN is to break the “itch-scratch” cycle. Keeping fingernails short or wearing gloves are simple things patients can do from home to help mitigate itching in addition to doctor-prescribed treatments.

• Topical Antipruritics: Creams containing 1% menthol or phenol aim to soothe and lessen the itch on the skin's surface¹
• Topical Glucocorticoids: Creams or ointments like betamethasone dipropionate and intralesional glucocorticoids, such as triamcinolone acetonide, are commonly employed to address inflammation and itching. Air-tight bandages are also utilised to disrupt the itch-scratch cycle¹
• Oral Medications: Antihistamines like promethazine and antidepressants such as doxepin are administered to combat pruritus¹
• UV Light Exposure: UV has shown good efficacy in breaking the cycle of itching and scratching¹⁰
• Cryotherapy: The application of liquid nitrogen to nodules helps by inducing controlled freezing, subsequently healing the skin¹
• Topical Vitamin D3: Has been shown to reduce both the number and size of nodules in PN patients¹¹
• Capsaicin: Applied topically, capsaicin can help to clear up lesions¹² 

Complications and prognosis

The intense scratching associated with  PN is an incredibly tough condition to live with. However, PN is also associated with several complications. Persistent scratching of nodules can lead to bleeding and, therefore, open wounds; without proper care, these wounds can become infected and lead to scarring and skin damage. 

PN can also take a toll on the patient's mental health. Body image issues may arise from the amount and placement of nodules which can lead to anxiety and depression.⁴ Mental health conditions can become exacerbated by disturbances in sleep and daily routine caused by itching. PN is a horrible condition that carries a large emotional burden that can last years, so it's incredibly important for those suffering from PN to have a strong support network. It may also be beneficial for patients to seek out counselling to help them through the course of the disease.

While prognosis varies among patients, some people may experience periods of remission, especially with effective treatment strategies.¹³ As such it is incredibly important to seek professional help if any symptoms of PN arise as early intervention is crucial for managing the condition and the complications associated with it.

FAQs

What is the main cause of Prurigo Nodularis?

The exact cause of PN is currently unknown, however, it is thought to be caused by a mix of neuronal and immune factors. Additionally, some environmental factors such as insect bites may trigger the disease.

What does a Prurigo look like?

PN consists of nodules and lesions a few millimetres to 2 centimetres in diameter, they are firm, itchy and can be discoloured. The amount of nodules varies greatly and can range from just a few to hundreds across the arm, legs and body.

How do you stop nodular prurigo?

Whilst there is no current cure for PN, there are plenty of topical and oral medications to help alleviate itching. Breaking the “itch-scratch” cycle is paramount for dealing with PN and if successful, remission can be achieved.

Is Prurigo Nodularis an autoimmune disorder?

The root cause of PN is still under investigation, however, some studies have suggested the onset of the disease is associated with the immune system. PN-related skin lesions have increased T lymphocytes, mast cells, and eosinophilic granulocytes. These immune cells release substances like interleukin-31 (IL-31) and histamine, causing inflammation and intense itching, a key aspect of PN. IL-31 induces itching by binding to specific receptors, and studies show that blocking IL-31 can reduce scratching. 

Summary

Prurigo nodularis is a chronic and distressing skin condition characterised by intensely itchy nodules, typically affecting the arms and legs. The persistent compulsion to scratch worsens the condition, leading to nodules, hyperpigmented macules, and scarring, impacting both physical appearance and mental well-being. While the exact cause remains elusive, research suggests a complex interplay of neurological and immune factors. 

Diagnosis involves clinical examination, symptom review, and laboratory tests. Management focuses on breaking the itch-scratch cycle, employing topical treatments, oral medications, UV exposure, and cryotherapy. Complications include skin damage, infections, and mental health issues. Prognosis varies, with some experiencing remission, emphasising the importance of early intervention and professional support.

PN is a tough condition to live with, as such it is essential to have a robust support network surrounding the patient. The disease can impact many areas of life, negatively impacting sleep, body issues and reluctance to be out in public. People suffering from mental health issues from PN should consider reaching out to mental health professionals and support groups.