PRACTICE RECOMMENDATIONS
› Start with topical corticosteroids under occlusion and periodically substitute with steroid-sparing agents (calcipotriol ointment or pimecrolimus 1% cream) for localized prurigo nodularis. B
› Consider adding oral antihistamines or montelukast to the initial regimen if a pruritic cause is suspected; alternatively, consider adding these agents if topical therapies alone do not effectively treat the prurigo nodules. C
› Turn to oral naltrexone, gabapentin, or pregabalin for more widespread or treatment-resistant cases. C
Strength of recommendation (SOR)
A Good-quality patient-oriented evidence
B Inconsistent or limited-quality patient-oriented evidence
C Consensus, usual practice, opinion, disease-oriented evidence, case series
CASE › A 43-year-old woman arrives at your office with persistent itching on her arms and legs. For some time, she has used moisturizing lotions and herbal preparations suggested by her mother, but they have provided no relief. You note multiple 0.5- to 2-cm firm, excoriated nodules symmetrically distributed on her elbows and knees bilaterally. She has seasonal allergies and a history of childhood asthma. How would you care for this patient?
Treating prurigo nodularis (PN) can be a daunting task for even the most experienced clinician. Prurigo nodules are cutaneous lesions often produced by repetitive scratching—hence the nickname “picker’s nodules”—which may occur as sequelae of chronic pruritus or neurotic excoriations. Thus, PN can be classified as a subtype of neurodermatitis. The nodules can be intensely pruritic, resulting in an itch-scratch cycle that can be difficult to break.1,2 In this review, we examine evidence-based therapies for PN.
Key findings with prurigo nodularis
Typically, prurigo nodules are firm, hyperkeratotic, pruritic papules or nodules that range in diameter from a few millimeters to several centimeters. The lesions usually have eroded or ulcerated components secondary to repeated excoriation, which can eventually lead to scarring and changes in pigmentation. Patients can have one nodule or hundreds of lesions, depending on disease severity. The lesions tend to be distributed symmetrically and have a predilection for the extensor surfaces of the upper and lower limbs. The abdomen, posterior neck, upper and lower back, and buttocks are also commonly affected, whereas the face, palms, and flexural areas are rarely involved2-5 (FIGURE 1).
The differential diagnosis for PN includes dermatitis herpetiformis, scabies, lichen simplex chronicus, hypertrophic lichen planus, perforating disorders, atopic dermatitis, allergic contact dermatitis, neurotic excoriations, and multiple keratoacanthomas.4,5
PN prevalence and etiology are unknown. Although PN can occur at any age, the typical age range is 20 to 60 years, with middle-aged women most commonly affected. Patients who develop PN at a younger age are more likely to have an atopic diathesis.3,4
There is ongoing debate regarding whether PN is a primary cutaneous disease or a response to repetitive scratching provoked by a separate cause. PN has been associated with a variety of diseases, such as psychiatric disorders, atopic dermatitis, chronic renal failure, hyperthyroidism, iron-deficiency anemia, obstructive biliary disease, gastric malignancy, lymphoma, leukemia, human immunodeficiency virus (HIV), hepatitis B, and hepatitis C.2,3
Use the diagnostic work-up to focus on management decisions
When taking the history, first determine why patients are picking or scratching. If the lesions are pruritic or painful, look for a potential underlying cause of pruritic symptoms.6 If you identify an underlying dermatologic or systemic condition, treat that disorder first.1 For example, adequately treating a patient’s atopic dermatitis or hyperthyroidism may quell the pruritic symptoms and potentially make the prurigo nodules more responsive to symptomatic treatment or even obviate the need for such measures.
If treating the underlying cause of PN does not provide adequate relief, or if no cause for pruritic nodules can be found, the nodules may yet respond to symptomatic treatments targeted at decreasing pruritus and inflammation. In contrast, with patients who habitually scratch lesions they describe as non-pruritic, neurotic excoriations could be the source of PN, making the nodules less likely to respond to antipruritic therapies.4,7
Patient insights. Assessing whether patients have insight into their condition is also important. Some patients may be unaware that they are repetitively picking and scratching the affected areas and causing the development and perpetuation of the nodules. In cases associated with an underlying psychiatric component, such as delusional parasitosis, patients often lack insight into their condition and thus may benefit from treatment of psychiatric comorbidities.4,7
On physical exam, try to find lesions that have not been traumatized by patients. They can be useful in uncovering a primary cause, such as scabies, atopic dermatitis, lichenoid drug eruption, or simple xerosis.
If a diagnosis cannot be made clinically, consider obtaining a biopsy of a nontraumatized lesion. Traumatized lesions are typically unrevealing on histopathology. If the clinical assessment of pruritic lesions is indeterminate, laboratory tests that may prove helpful include, but are not limited to, thyroid-stimulating hormone levels, liver function tests, kidney function, a hepatitis panel, and HIV screening.