Assessing disease severity in prurigo nodularis
The information and resources included below can help you educate your patients about Prurigo Nodularis and how the disease is diagnosed and managed.
Do we need a unified assessment tool to measure psychosocial impact?
Prurigo Nodularis (PN) is a skin disease characterized by the presence of severely itchy skin lesions, such as nodules or papules, which are caused by scratching over a prolonged period. PN usually presents as multiple, intensely pruritic, excoriated nodules on the arms and legs and occasionally the trunk.1
PN can be clinically characterized by several parameters, including the type of lesions (papules, nodules, plaques), their size and quantity, elevation, distribution, stage of healing (resolution), and signs of scratch activity, such as excoriations and crusts.2
To date, there is no uniform documentation available for quick and easy diagnosis of disease and severity. Zeidler et al. sought to address this by validating a new assessment tool that would provide uniform documentation for skin lesions in PN and a well-accepted and clinically meaningful assessment tool for use in clinical trials and eventually clinical practice.
One tool that may satisfy the need for a standard diagnostic is the Investigator’s Global Assessment (IGA).3 The IGA provides a tool that will help bring consistency to how disease severity and progression are measured and understood. The instrument is divided into two parts: one for the total number of skin lesions and one for the proportion of excoriations on existing lesions. The number of lesions determines the stage of the disease and the presence and extent of excoriations determine its current activity.
The IGA covers chronic prurigo (CPG), chronic nodular prurigo (CNPG, the most common subtype of the disease) and chronic prurigo activity (CPG activity or excoriations).3
Prurigo Activity and Severity (PAS) score is another assessment tool for PN, providing a composite assessment of severity, activity and distribution of PN over time. PAS was created by Pölking et al. in 2018 to provide a more contextual view of chronic prurigo severity over time. The 7-item PAS questionnaire is often used in concert with the IGA to design and populate clinical trials. The instruments are also used in clinical practice.4
Beyond the physical impact of the condition, truly understanding the burden in PN must also consider its psychosocial burden. Brenaut et al. illuminated the psychological burden in PN and found the impact and severity of PN on quality of life to be significant, with half of patients in their 5,000-person study describing it as “very large” or “extreme.”5
Patients with PN often experience impaired quality of life, sleep disturbance, anxiety, and depression. Pruritus and the extent of body surface area involved become so great for some patients that they no longer feel functional for work or other everyday activities.6 However, although there is strong consensus on the psychosocial impact of PN, there is no hard consensus on the best instruments to measure it.
The Dermatology Life Quality Index (DLQI) is used most commonly.7 Initially published in 1994, the DLQI consists of 10 questions concerning patients' perception of the impact of skin diseases on different aspects of their health-related quality of life over the previous week.8
The development and validation of a PN-specific DLQI
More about PN
The exact cause of PN is not well-understood though it is thought that nodules are more likely to form when skin has been scratched or irritated in some way. The condition appears to result from a repetitive itch-scratch cycle induced by neuronal sensitization to chronic pruritus. The act of a person scratching skin can trigger this process.9, 10
Although the exact cause of itching in PN is not known, symptoms are thought to stem from dysregulation of the nerves and immune system in the skin of the affected area. The itching leads to repetitive rubbing, scratching and touching, which causes the skin to thicken and form plaques or nodular lichenification and hyperkeratosis.11
PN nodules or papules are 3-20 mm in diameter and may number from 1-2 to hundreds. They present as discrete, scaly, generally symmetric, hyperpigmented or purpuric, and firm. Prurigo Nodularis lesions may show signs of excoriation with flat, umbilicated, or crusted top.11
PN can occur on its own or can be associated with skin diseases (dermatoses) or with infections, systemic diseases, neurological conditions or psychiatric conditions. In more than half of patients, PN is associated with an underlying dermatologic condition, typically a pruritic condition such as atopic dermatitis. For most patients, multiple underlying causes are identified. The severity and outcome of PN are not predicted by the underlying cause.12
Though PN is benign and does not increase mortality, some conditions associated with the condition may cause mortality. PN has been documented to be much more common in immunocompromised and HIV populations and some cases of PN are associated with internal malignancy, notably lymphoma. PN may also be an early manifestation of severely decreased kidney function.13
The number of new cases of PN per year in the US is estimated to be greater than 87,000 people/year aged 18 to 64. While PN can occur at any age, it is more likely to occur between ages 40 to 69 years old. Younger patients with PN are more likely to have other skin disorders associated with allergic states, such as eczema. 14
The condition is more common in women (54.2%) compared to men (45.5%). Women with PN also experience more severe pruritus. Notably, PN is 3.4 times more common in African Americans than Caucasian Americans.15