Prurigo nodularis

Signs and symptoms

• Nodules are discrete, generally symmetric, hyperpigmented and firm. They are greater than 0.5 cm in both width and depth (as opposed to papules which are less than 0.5 cm).
• The nodules of PN can appear on any part of the body, but generally are found in areas where patients are able to reach to scratch. Patients can exhibit a 'butterfly sign' in which nodules are absent in the mid upper back.
• Nodular lesions are often excoriated from persistent scratching.
• The nodules in PN are extremely itchy, and this sensation can have an impact on patients perceived quality of life
• Nodule pattern can be follicular.

Causes

The exact cause of prurigo nodularis is unknown; however, it is thought to be induced by other dermatologic conditions such as severe atopic dermatitis, Becker's nevus, and linear IgA disease. PN is also associated with systemic causes of pruritus such as liver disease, cholestasis, thyroid disease, polycythemia vera, uremia, Hodgkin lymphoma, HIV and kidney failure diseases. Psychiatric illnesses have been considered to induce PN, although later research refuted a psychiatric cause for PN. Patients report an ongoing battle to distinguish themselves from those with psychiatric disorders, such as delusions of parasitosis and other psychiatric conditions.

Pathophysiology

Chronic and repetitive scratching, picking, or rubbing of the nodules may result in permanent changes to the skin, including nodular lichenification, hyperkeratosis, hyperpigmentation, and skin thickening. Unhealed, excoriated lesions are often scaly, crusted or scabbed. Many patients report a lack of wound healing even when medications relieve the itching and consequent scratching.

Patients often:

• seek treatment during middle-age, although PN can occur at any age
• have a history of chronic severe pruritus
• have a significant medical history for unrelated conditions
• develop liver or kidney dysfunctions
• develop secondary skin infections
• have a personal or family history of atopic dermatitis
• have other autoimmune disorders
• have low vitamin D levels.

Diagnosis

Diagnosis is based on visual examination and the presence of itching for greater than 6 weeks duration.

A skin biopsy is often performed to exclude other diseases. Lesion biopsies usually show light inflammation, sometimes with increased numbers of eosinophils. A culture of at least one lesion will rule out staphylococcus infection, which has been significantly linked to atopic dermatitis.

Treatment

PN is hard to treat and therapies include steroids, dupilumab, vitamins, cryosurgery, thalidomide, and UVB light. In the event that staphylococcus or other infection is present, antibiotics have proven effective, but tend to cause more harm than good for this particular disease. A physician may administer a strong dose of prednisone, which will almost immediately stop the itch/scratch cycle. However, cessation of steroids allows relapse to occur, usually within a few weeks. A 2006 study reported improvement in PN with antibiotic therapy.

Azathioprine (Imuran), an immunosuppressive drug used in organ transplantation and autoimmune diseases and belonging to the chemical class of purine, has been reported to be effective.

Dupilumab (Dupixent) was approved for medical use in the United States in September 2022. Dupilumab is the first medication approved for the treatment of PN by the US Food and Drug Administration.

Nemolizumab (Nemluvio) was approved for medical use in the United States in August 2024.

History

PN was first described by Hyde and Montgomery in 1909.

Notes

References

1. (May 2021). "Prurigo Nodularis: Review and Emerging Treatments". Skin Therapy Letter.
2. "Prurigo nodularis: Causes".
3. (13 April 2022). "Non-Atopic Chronic Nodular Prurigo (Prurigo Nodularis Hyde): A Systematic Review of Best-Evidenced Treatment Options". Dermatology.
4. (December 2020). "Prurigo nodularis". Journal of the American Academy of Dermatology.
5. (1 July 2022). "Chronic itch in African Americans: an unmet need". Archives of Dermatological Research.
6. (December 2006). "Eczematous dermatitis and prurigo nodularis confined to a Becker's nevus". International Journal of Dermatology.
7. (August 2006). "Linear IgA disease presenting as prurigo nodularis". The British Journal of Dermatology.
8. (October 2009). "Recognizing and treating cutaneous signs of liver disease". Cleveland Clinic Journal of Medicine.
9. (July 2004). "Itch: a symptom of occult disease". Australian Family Physician.
10. (November 1995). "Prurigo nodularis and photosensitivity in AIDS: treatment with thalidomide". Journal of the American Academy of Dermatology.
11. (2006). "[The role of psychological factors and psychiatric disorders in skin diseases]". Medycyna Pracy.
12. (April 2018). "[Influence of anxiety in diverse cutaneous diseases]". Actas Dermo-Sifiliograficas.
13. (26 September 2019). "Diagnostic Workup and Evaluation of Patients with Prurigo Nodularis". Medicines.
14. (August 2000). "Eosinophil cationic protein- and eosinophil-derived neurotoxin/eosinophil protein X-immunoreactive eosinophils in prurigo nodularis". Archives of Dermatological Research.
15. (October 2006). "Skin colonization by Staphylococcus aureus in patients with eczema and atopic dermatitis and relevant combined topical therapy: a double-blind multicentre randomized controlled trial". The British Journal of Dermatology.
16. (December 2007). "Role of bacterial pathogens in atopic dermatitis". Clinical Reviews in Allergy & Immunology.
17. (April 2005). "Persistent skin colonization with Staphylococcus aureus in atopic dermatitis: relationship to clinical and immunological parameters". Clinical and Experimental Allergy.
18. (April 2006). "Uncontrollable prurigo nodularis effectively treated by roxithromycin and tranilast". Journal of Drugs in Dermatology.
19. (2023). "Amitriptyline and azathioprine: an effective therapeutic approach in PN resistant to conventional therapies". JDDG: Journal der Deutschen Dermatologischen Gesellschaft.
20. (1996). "Nodular prurigo responsive to azathioprine (letter)". British Journal of Dermatology.
21. (29 September 2022). "FDA approves first treatment for prurigo nodularis". U.S. [[Food and Drug Administration]] (FDA).
22. (13 August 2024). "Galderma Receives U.S. FDA Approval for Nemluvio (nemolizumab) for Adult Patients Living With Prurigo Nodularis". Galderma.
23. Hyde JN, Montgomery FH: A practical treatise on disease of the skin for the use of students and practitioners. 1909; 174–175.