Nodular Prurigo

Medically reviewed by The Dermatologists and written by Dr. Alexander Börve

Nodular Prurigo (NP) is a chronic skin condition characterized by the presence of itchy firm lumps, impacting individuals’ quality of life significantly.

This condition, prevalent among older adults, is associated with atopy, chronic itch-inducing drugs, and internal diseases like cancer, diabetes, and liver disease.

Despite its severity and chronic nature, the exact cause of NP remains unknown, with potential links to nerve dysregulation and immune system activity, exacerbated by environmental triggers such as insect bites and stress.

What is Nodular Prurigo?

Nodular Prurigo (NP) stands as a dermatological condition characterized by the development of persistent, intensely itchy nodules or papules on the skin.^[1]

Characteristics of NP Lesions

• Appearance: The lesions of NP present as raised, often rounded nodules or papules that are significantly excoriated due to the chronic nature of the itching and scratching involved. Over time, these nodules may develop a crust or scab on their surface due to repeated trauma.
• Color: They frequently exhibit a hyperpigmented appearance, which is a result of the chronic inflammation and the ongoing cycle of itching and scratching.^[2] This hyperpigmentation indicates the chronicity of the condition and the persistent trauma to the skin.
• Size and Distribution: The size of the nodules can vary, ranging from a few millimeters to several centimeters in diameter. They tend to appear in clusters and are primarily located in areas that are easily accessible to scratching. This includes limbs, especially the lower legs, arms, and sometimes the trunk.
• Texture and Sensation: The texture of these nodules is typically firm, and they can be tender or painful to the touch. The overlying skin may feel thickened, and there’s often a central point that may look like a punctum, which is a hallmark of the condition.
• Chronicity and Recurrence: NP is known for its chronic course, with nodules that may persist for weeks to months. New lesions can appear as older ones begin to heal, contributing to the chronic and relapsing nature of the condition.

The Itch-Prurigo Cycle: How It Leads to NP

The insidious nature of Nodular Prurigo is closely tied to the incessant itch that precedes its development. The condition often emerges as a consequence of chronic pruritus, compelling individuals to scratch persistently.^[3] This continual scratching exacerbates the initial pruritus, creating a detrimental cycle known as the itch-prurigo cycle. The more a person scratches, the more nodules develop, leading to a self-perpetuating cycle of discomfort and exacerbation of the skin lesions.

Who is at Risk & Risk Factors

Nodular Prurigo (NP) predominantly affects older adults, highlighting this demographic group as particularly vulnerable to this chronic skin condition.^[4] The prevalence of NP increases with age, underscoring the significance of age-related factors in its development and manifestation.

Association with Various Factors

• Atopy: Individuals with a history of atopy, characterized by allergic conditions like eczema and asthma, are at an increased risk of developing NP.^[5] The underlying immune dysregulation associated with atopy may contribute to the pathogenesis of NP.
• Chronic Itch-Inducing Drugs: Certain medications known to induce chronic itching can predispose individuals to NP. The prolonged exposure to these drugs can trigger persistent itchiness, leading to the development of nodules characteristic of NP.
• Internal Diseases: NP has been linked to internal diseases such as cancer, diabetes, and liver disease.^[6] The presence of these underlying conditions can exacerbate the severity of NP and complicate its management, emphasizing the importance of addressing systemic health issues in individuals with NP.

Causes and How It Happens

Exploration of NP’s Unknown Exact Cause

The exact cause of Nodular Prurigo (NP) remains elusive, adding to the complexity of understanding and managing this chronic skin condition. While the precise etiology is unknown, potential links have been suggested, including:

• Nerve Dysregulation: NP may be associated with nerve dysregulation, where abnormal signaling in the nervous system contributes to the development and persistence of itch and nodules characteristic of NP.
• Immune System Activity: Dysregulation in immune system activity has also been implicated in the pathophysiology of NP. Immune responses within the skin may play a role in triggering and perpetuating the inflammatory processes underlying NP.^[7]

Environmental Triggers

• Insect Bites: Insect bites can provoke intense itching and skin irritation, potentially triggering the onset or exacerbation of NP in susceptible individuals.^[8]
• Stress: Psychological stress has been linked to worsening skin conditions, including NP. Stress-induced changes in immune function and inflammatory responses may exacerbate itchiness and inflammation, further complicating the management of NP.

Diagnostic Process for Nodular Prurigo

• The diagnosis of Nodular Prurigo relies on a thorough clinical evaluation, taking into account the characteristic presentation of  symmetrically distributed pruritic nodules and papules.
• Dermatologists may opt for skin biopsy to confirm the diagnosis, particularly in cases where the clinical features are ambiguous or other dermatological conditions need to be ruled out.
• Skin biopsy specimens typically reveal epidermal hyperplasia, dermal fibrosis, and a mixed inflammatory infiltrate, supporting the diagnosis of NP.

Accurate Diagnosis: Distinguishing NP from Similar Conditions

Conditions such as:

• prurigo simplex
• atopic dermatitis
• allergic contact dermatitis
• dermatitis herpetiformis

may share clinical similarities with NP, necessitating careful consideration and exclusion.

Common Treatment Options for NP

• Topical Therapies: Topical treatments, such as emollients and corticosteroids, can help alleviate itchiness and inflammation associated with NP. These therapies are often used as a first-line treatment and can be effective in managing mild to moderate cases of NP.^[11]
• Phototherapy: Phototherapy, including ultraviolet B (UVB) and narrowband UVB (NB-UVB), can be used to reduce inflammation and itchiness in NP. This treatment modality is particularly beneficial for individuals with extensive involvement of the skin.
• Systemic Treatments: Systemic treatments, such as antihistamines and immunosuppressive agents, can be employed to manage severe cases of NP. These therapies can help alleviate itchiness and reduce the progression of nodules.
• Emerging Therapies: Emerging therapies, such as monoclonal antibodies, are being explored for their potential in treating NP. These novel treatments may offer new avenues for managing this challenging skin condition.

Occurrence of Nodular Prurigo in Darker Skin Tones

In darker skin, NP lesions may appear firmer, larger, and darker in color compared to those observed in lighter-skinned individuals.

Hyperpigmentation and post-inflammatory changes are more pronounced in darker skin, contributing to the characteristic dark hue of NP nodules.^[13]

Healthcare providers must be attuned to the differences in clinical presentation and adjust their diagnostic approach accordingly, considering the potential for misdiagnosis or delayed diagnosis in individuals with darker skin tones.