Prurigo pigmentosa: A multi-institutional retrospective study

To the Editor: Prurigo pigmentosa (PP) is an inflammatory skin disease characterized by a sudden eruption of pruritic, erythematous papules in a reticular pattern followed by hyperpigmentation.1Nagashima M. Prurigo pigmentosa--clinical observations of our 14 cases.J Dermatol. 1978; 5: 61-67https://doi.org/10.1111/j.1346-8138.1978.tb01049.xCrossref PubMed Scopus (95) Google Scholar In recent years, PP has been anecdotally associated with the ketogenic diet.2Delaleu J. Grynberg-Laloum E. Moguelet P. et al.Prurigo pigmentosa induced by ketosis ("keto rash"): a demonstrative case and internet search results.Int J Dermatol. 2020; 59: 876-877https://doi.org/10.1111/ijd.14873Crossref PubMed Scopus (6) Google Scholar However, studies on PP have been limited to small case series. Our retrospective study examined the largest pool of PP patients to date from 3 academic centers in the United States over a 10-year period to identify potential triggers, comorbidities, and treatments. We searched dermatology records from the University of California, Los Angeles, the University of Virginia, and the Mass General Brigham Hospital System from 2011-2021 using the search term "prurigo pigmentosa." We identified 30 patients with a confirmed diagnosis of PP; demographic and clinical factors were abstracted. Of the 30 patients, 21 were female (Table I). The average age was 41 years, and the median age was 37 (range: 18-74 years). The majority of patients were White (56%) followed by Asian (30%). Twenty-nine patients had a body mass index >25 kg/m2. All patients presented with erythematous papules coalescing into plaques with a background of reticulated hyperpigmentation with or without scale, and all patients endorsed pruritus. The most commonly affected sites were back (46%) and chest (43%). Of the patients, 40% (12/30) were on a ketogenic diet prior to the onset of symptoms. Three patients were prediabetic, and none were diabetic. Eleven patients had hyperlipidemia. None of the patients had autoimmune conditions. Histopathological findings for PP were subtle and nonspecific—common features of the 13 available records were very mild spongiosis and a predominantly lymphoplasmacytic perivascular and interstitial infiltrate. Neutrophils and eosinophils were rare. All patients received treatment. Topical corticosteroids (12/30) only provided temporary relief, whereas oral antibiotics (11/30) led to complete resolution in all treated patients.Table IClinical and demographic characteristics of individuals with prurigo pigmentosa (N = 30)No. of patients, n (%)DemographicsSex Female21 (70) Male9 (30)Race White17 (56) Asian9 (30) Black2 (6) Other2 (6)Morphologies Hyperpigmentation30 (100) Papules30 (100) Scaling15 (50)Symptoms Pruritus30 (100) Pain0 (0)Distribution Chest13 (43) Back14 (46) Upper extremities3 (10) Lower extremities2 (6)Diet Ketogenic diet12 (40) Low carbohydrate diet3 (10) Normal diet15 (50)BMI, kg/m2 ≤18.50 (0) 18.5-24.91 (3) 25.0-29.921 (70) ≥ 30.08 (26)Comorbidities Hyperlipidemia11 (36) Hypothyroidism3 (10) H. pylori1 (3) Allergic rhinitis1 (3) Asthma0 (0) Diabetes mellitus0 (0) Hyperthyroidism0 (0) Pregnancy0 (0) Sjogren's0 (0) Lupus0 (0) Dermatomyositis0 (0) Scleroderma0 (0) Rheumatoid arthritis0 (0) Mixed connective-tissue disease0 (0)Skin specific comorbidities Atopic dermatitis3 (10) Acne vulgaris3 (10) Allergic contact dermatitis3 (10) Psoriasis2 (6) Pityriasis rosea1 (3) Prurigo nodularis1 (3) Telogen effluvium1 (3)Treatment Topical corticosteroids12 (40)Triamcinolone 0.1%6 (20)Betamethasone 0.05%3 (10)Hydrocortisone 2.5%1 (3)Fluocinolone 0.025%1 (3)Clobetasol 0.05%1 (3) Oral doxycycline6 (20) Oral minocycline5 (16) Topical ketoconazole2 (6) Topical tacrolimus1 (3) Oral prednisone1 (3) Transition to normal diet3 (10) Open table in a new tab Our study supports the classic presentation of PP as documented in the literature and finds pruritus to be a constant feature. Most individuals with PP across the institutions were either White or Asian females, consistent with demographics reported in the literature.3Seol J.E. Cho G.J. Park S.H. Kim H. Prurigo pigmentosa: an institutional retrospective study of 24 patients.Australas J Dermatol. 2021; 62: 70-72https://doi.org/10.1111/ajd.13435Crossref PubMed Scopus (4) Google Scholar PP did not seem to be associated with autoimmune conditions, despite previous reports detailing a likely association.4Togawa Y. Shinkai H. Utani A. Prurigo pigmentosa in a patient with primary biliary cirrhosis and Sjögren syndrome.J Dermatol. 2004; 31: 815-819https://doi.org/10.1111/j.1346-8138.2004.tb00606.xCrossref PubMed Scopus (12) Google Scholar Atopic diathesis has been postulated to be associated with PP.5Kwon H.J. Kim M.Y. Kim H.O. Park Y.M. Two cases of prurigo pigmentosa in atopic patients.J Dermatol. 2006; 33: 579-582https://doi.org/10.1111/j.1346-8138.2006.00136.xCrossref PubMed Scopus (21) Google Scholar Our data did not show a strong association of PP with the 3 most common atopic conditions. Our finding of higher body mass index in nearly all PP patients has not been reported elsewhere and may be worth exploring in future studies. Based on our results, we did not clearly identify a unifying, common trigger of PP, suggesting different etiologies not limited to the ketogenic diet. Biopsy may assist in ruling out other diagnoses but is not diagnostic of PP on its own. PP affects a wide range of ages and both sexes, with a female predilection. Furthermore, a course of oral antibiotics (doxycycline or minocycline 100 mg twice daily for 1 to 2 months) may be considered in PP cases where transition to normal diet or topical treatment does not lead to complete resolution. None disclosed.