Dermatological Conditions in Skin of Color: An Update on Prurigo Nodularis in Skin of Color

by Archana M. Sangha, MMS, PA-C

Ms. Sangha is a senior medical science liaison for Incyte Corporation in Wilmington, Delaware. Prior to that, she spent over a decade as a dermatology PA specializing in general, surgical, and cosmetic dermatology. She is a fellow of the American Academy of Physician Assistants in Alexandria, Virginia. She is also a Past President of the Society of Dermatology Physician Assistants.

Funding: No funding was provided for this article.

Disclosures: Ms. Sangha is an employee of Incyte Corporation in Wilmington, Delaware.

J Clin Aesthet Dermatol. 2024;17(9–10 Suppl 1):S28–S29.

Prurigo nodularis (PN) is a chronic inflammatory disease that has an estimated overall prevalence of 72 per 100,000 people in the United States (US). It has an increased incidence in older adults, as is evidenced by its prevalence of nearly 148.3 per 100,000 people in the US Medicare population.^1–4

PN presents with multiple papules or nodules that are well circumscribed, scaly, symmetric, firm, hyperpigmented, or purpuric. They often affect the extensor surfaces of the arms and legs and are intensely pruritic.⁵

This article will discuss recent research in the pathophysiology of PN and how that might impact your care of patients with skin of color (SOC).

It is a chronic inflammatory skin disorder. Those of us who have practiced for many years can recall being initially taught that PN was a “picker’s nodule.” We learned that the lesions were often isolated and to counsel our patients “not to pick.” We were advised to treat the lesion(s) with topical corticosteroids, intralesional triamcinolone, etc.⁵ If the patient followed our instructions and didn’t pick, the lesion(s) would resolve.

Recent research has shown that PN is not simply a “picker’s nodule,” but rather a chronic condition with a complex immunopathogenesis that includes neuroimmune-inflammatory pathways. We now know that certain cytokines (i.e., interleukin-4, -13, -17, -22, and -31) released from T cells increase systemic inflammation in patients with PN.⁶ Additionally, the irretractable pruritis often described by patients could be in part due to the decreased density of intraepidermal nerve fibers, which are found to be thin and unmyelinated in patients with PN, as well as the increased density of dermal nerve fibers.⁵ Further research needs to be done to more clearly understand the complex pathogenesis of PN.

Black patients are more likely to have PN and to have more severe disease. Studies have shown that Black patients are up to 3.4 to 4.4 times more likely to have PN than White patients.^7,8 Additionally, PN lesions in African American patients were found to be more densely fibrotic, larger, and more likely to be recalcitrant to treatment than those found in White patients.^6,9 Contrast that with PN lesions in White patients, which are often shallower and more ulcerative.⁶

PN is associated with several comorbidities. In one study where patients with PN were compared with race-matched controls, patients with PN were found to have statistically higher rates of cardiovascular disease, chronic obstructive pulmonary disease, and major depressive disorder.⁷ Other studies have also found an association with Type 2 diabetes, chronic kidney disease, and hepatitis C.^2,8,9

A study by Boozalis et al⁸ found that PN was more prevalent in African American patients with human immunodeficiency virus (HIV) infection but not White patients with HIV infection. Furthermore, they found that Black patients with PN were 10.5 times more likely to have HIV than race-matched controls with atopic dermatitis (AD), and eight times more likely to have HIV than race-matched controls with psoriasis.⁸ While more research is needed to understand the correlation between PN, HIV, and African American patients, clinicians should include HIV antibodies in their workup when appropriate.¹⁰

While there remains a paucity of data globally, one multicenter retrospective study looking at 759 patients with PN in China found the most common comorbidities to be allergic rhinitis (22%), AD (12.3%), and food allergy (5.3%). While the study did not list depression and anxiety as comorbidities, it should be noted that 29.7 percent of patients had Hospital Anxiety and Depression Scale (HADS) scores that indicated anxiety or depression symptoms.¹⁰

In a retrospective database analysis of 2,743 patients in England, the authors found the most common comorbidities to be AD (52.2%), depression (41.1%), anxiety (35.4%), and Type 2 diabetes (17.6%). Of note, only a small proportion of patients had an HIV diagnosis (0.2%).¹¹

Many more global studies are needed to understand PN across a variety of ethnicities.

PN has the most significant quality of life impact among all chronic pruritic dermatoses.¹² In a multicenter European cross-sectional study of over 500 adult patients with chronic pruritis and inflammatory dermatoses, patients with PN were found to have the greatest impairment in quality of life (QoL), as well as the largest intensity and frequency of pruritis. The study also found that compared to other pruritic dermatological conditions (e.g., AD, lichen planus, psoriasis, etc.), patients with PN experienced greater nighttime pruritis (77.1%). The authors concluded that this increase in nighttime pruritis might be why the QoL impairment was noted to be the greatest in patients with PN, with 60 percent saying their disease often or always impacted activities of daily living.¹³

Black skin has unique biological features that make it more susceptible to pruritis. These features include increase in transepidermal water loss, decreased ceramides in the stratum corneum, lower pH in the stratum corneum, and increased mast cell size.⁷ Also recall that typical signs of erythema are more difficult to appreciate in dark skin and often present with as an ashen-gray, darker brown or violaceous hue, if at all. Thus, your index of suspicion for the burden of pruritis in Black skin should be heightened.

References

1. Whang KA, Kang S, Kwatra SG. Inpatient burden of prurigo nodularis in the United States. Medicines (Basel). 2019;6(3):88.
2. Huang AH, Canner JK, Khanna R, Kang S, Kwatra SG. Real-world prevalence of prurigo nodularis and burden of associated diseases. J Invest Dermatol. 2020;140(2):480–483.e4.
3. Huang AH, Williams KA, Kwatra SG. Prurigo nodularis: epidemiology and clinical features. J Am Acad Dermatol. 2020;83(6):1559–1565.
4. Ständer S, Augustin M, Berger T, et al. Prevalence of prurigo nodularis in the United States of America: a retrospective database analysis. JAAD Int. 2020;2:28–30.
5. Mullins TB, Sharma P, Riley CA, et al. Prurigo nodularis. Updated 1 Mar 2024. In: StatPearls. Treasure Island (FL): StatPearls Publishing; 2024. https://www.ncbi.nlm.nih.gov/books/NBK459204/
6. Liao V, Cornman HL, Ma E, Kwatra SG. Prurigo nodularis: new insights into pathogenesis and novel therapeutics. Br J Dermatol. 2024;190(6):798–810.
7. McColl M, Boozalis E, Aguh C, et al. Pruritus in Black skin: unique molecular characteristics and clinical features. J Natl Med Assoc. 2021;113(1):30–38.
8. Boozalis E, Tang O, Patel S, et al. Ethnic differences and comorbidities of 909 prurigo nodularis patients. J Am Acad Dermatol. 2018;79(4):714–719.e3.
9. Sutaria N, Alphonse MP, Marani M, et al. Cluster analysis of circulating plasma biomarkers in prurigo nodularis reveals a distinct systemic inflammatory signature in African Americans. J Invest Dermatol. 2022;142(5):1300–1308.e3.
10. Yin M, Zhong W, Zhou K, Dou X. Comorbidities of prurigo nodularis in Chinese patients: a multicenter retrospective study. Chin Med J (Engl). 2024;137(11):1360–1362.
11. Morgan CL, Thomas M, Ständer S, et al. Epidemiology of prurigo nodularis in England: a retrospective database analysis. Br J Dermatol. 2022;187(2):188–195.
12. Belzberg M, Alphonse MP, Brown I, et al. Prurigo nodularis is characterized by systemic and cutaneous T helper 22 immune polarization. J Invest Dermatol. 2021;141(9):2208–2218.e14.
13. Steinke S, Zeidler C, Riepe C, et al. Humanistic burden of chronic pruritus in patients with inflammatory dermatoses: Results of the European Academy of Dermatology and Venereology Network on Assessment of Severity and Burden of Pruritus (PruNet) cross-sectional trial. J Am Acad Dermatol. 2018;79(3):457–463.e5.